From 4e21188efeca88bac1c326e4ae9726a0732e5ef6 Mon Sep 17 00:00:00 2001
From: James Jackson-South <james_south@hotmail.com>
Date: Wed, 26 Feb 2025 14:35:54 +1000
Subject: [PATCH 01/18] Fix all known quantizing issues

---
 src/ImageSharp/Common/InlineArray.cs          |  29 +
 src/ImageSharp/Common/InlineArray.tt          |  38 +
 src/ImageSharp/Formats/Bmp/BmpMetadata.cs     |   3 +-
 .../Formats/Cur/CurFrameMetadata.cs           |   1 +
 src/ImageSharp/Formats/Cur/CurMetadata.cs     |   3 +-
 src/ImageSharp/Formats/EncodingUtilities.cs   |  39 +-
 src/ImageSharp/Formats/Gif/GifDecoderCore.cs  | 141 +++-
 src/ImageSharp/Formats/Gif/GifEncoderCore.cs  |  93 ++-
 .../Formats/Gif/GifFrameMetadata.cs           |   3 +-
 src/ImageSharp/Formats/Gif/GifMetadata.cs     |  12 +-
 .../Formats/IFormatFrameMetadata.cs           |   6 +-
 src/ImageSharp/Formats/IFormatMetadata.cs     |   8 +-
 .../Formats/IQuantizingImageEncoder.cs        |   4 +-
 .../Formats/Ico/IcoFrameMetadata.cs           |   1 +
 src/ImageSharp/Formats/Ico/IcoMetadata.cs     |   3 +-
 src/ImageSharp/Formats/Png/PngEncoder.cs      |  12 -
 src/ImageSharp/Formats/Png/PngEncoderCore.cs  | 246 +++---
 src/ImageSharp/Formats/Png/PngMetadata.cs     |   3 +-
 .../Formats/TransparentColorMode.cs           |   2 +-
 .../Formats/Webp/BitReader/BitReaderBase.cs   |   2 +-
 .../Formats/Webp/Lossy/Vp8Decoder.cs          |  14 +-
 .../Formats/Webp/WebpAnimationDecoder.cs      | 110 ++-
 .../Formats/Webp/WebpCommonUtils.cs           |   2 +-
 src/ImageSharp/ImageSharp.csproj              |  14 +
 src/ImageSharp/IndexedImageFrame{TPixel}.cs   |   4 +-
 .../CloningImageProcessor{TPixel}.cs          |   6 +-
 .../Processors/Dithering/IDither.cs           |   4 +-
 .../IPaletteDitherImageProcessor{TPixel}.cs   |   8 +-
 .../Processors/ImageProcessor{TPixel}.cs      |   7 +-
 .../Quantization/EuclideanPixelMap{TPixel}.cs | 521 +++++++++---
 .../Quantization/IQuantizer{TPixel}.cs        |  12 +-
 .../Quantization/OctreeQuantizer{TPixel}.cs   | 766 +++++++++++++++---
 .../Quantization/PaletteQuantizer.cs          |  23 +-
 .../Quantization/PaletteQuantizer{TPixel}.cs  |  55 +-
 .../Quantization/QuantizerConstants.cs        |  19 +-
 .../Quantization/QuantizerOptions.cs          |  11 +
 .../Quantization/QuantizerUtilities.cs        |  38 +-
 .../Quantization/WuQuantizer{TPixel}.cs       |  71 +-
 .../Transforms/TransformProcessor{TPixel}.cs  |  15 +-
 .../Formats/Gif/GifEncoderTests.cs            |  11 +
 .../Formats/Png/PngEncoderTests.cs            |  46 +-
 .../Formats/WebP/WebpCommonUtilsTests.cs      |   4 +-
 .../Formats/WebP/WebpDecoderTests.cs          |  16 +
 .../ImageSharp.Tests/Image/ImageFrameTests.cs |   2 +-
 tests/ImageSharp.Tests/Image/ImageTests.cs    |   2 +-
 .../Quantization/WuQuantizerTests.cs          |   4 +-
 tests/ImageSharp.Tests/TestImages.cs          |   2 +
 .../ReferenceCodecs/MagickReferenceDecoder.cs |  36 +-
 ...de_8BitColor_WithOctreeQuantizer_rgb32.bmp |   2 +-
 ...Encode_8BitColor_WithWuQuantizer_rgb32.bmp |   2 +-
 ...onFilterInBox_Rgba32_CalliphoraPartial.png |   4 +-
 ...erFilterInBox_Rgba32_CalliphoraPartial.png |   4 +-
 ...rksWithAllErrorDiffusers_Bike_Atkinson.png |   4 +-
 ..._WorksWithAllErrorDiffusers_Bike_Burks.png |   4 +-
 ...hAllErrorDiffusers_Bike_FloydSteinberg.png |   4 +-
 ...lErrorDiffusers_Bike_JarvisJudiceNinke.png |   4 +-
 ...orksWithAllErrorDiffusers_Bike_Sierra2.png |   4 +-
 ...orksWithAllErrorDiffusers_Bike_Sierra3.png |   4 +-
 ...sWithAllErrorDiffusers_Bike_SierraLite.png |   4 +-
 ...thAllErrorDiffusers_Bike_StevensonArce.png |   4 +-
 ...WorksWithAllErrorDiffusers_Bike_Stucki.png |   4 +-
 ...orDiffusers_CalliphoraPartial_Atkinson.png |   4 +-
 ...ErrorDiffusers_CalliphoraPartial_Burks.png |   4 +-
 ...users_CalliphoraPartial_FloydSteinberg.png |   4 +-
 ...rs_CalliphoraPartial_JarvisJudiceNinke.png |   4 +-
 ...rorDiffusers_CalliphoraPartial_Sierra2.png |   4 +-
 ...rorDiffusers_CalliphoraPartial_Sierra3.png |   4 +-
 ...Diffusers_CalliphoraPartial_SierraLite.png |   4 +-
 ...fusers_CalliphoraPartial_StevensonArce.png |   4 +-
 ...rrorDiffusers_CalliphoraPartial_Stucki.png |   4 +-
 ...DependOnSinglePixelType_Bgra32_filter0.png |   4 +-
 ...tDependOnSinglePixelType_Rgb24_filter0.png |   4 +-
 ...DependOnSinglePixelType_Rgba32_filter0.png |   4 +-
 ...ndOnSinglePixelType_RgbaVector_filter0.png |   4 +-
 ..._WorksWithAllDitherers_Bike_Bayer16x16.png |   4 +-
 ...er_WorksWithAllDitherers_Bike_Bayer2x2.png |   4 +-
 ...er_WorksWithAllDitherers_Bike_Bayer4x4.png |   4 +-
 ...er_WorksWithAllDitherers_Bike_Bayer8x8.png |   4 +-
 ..._WorksWithAllDitherers_Bike_Ordered3x3.png |   4 +-
 ...Ditherers_CalliphoraPartial_Bayer16x16.png |   4 +-
 ...llDitherers_CalliphoraPartial_Bayer2x2.png |   4 +-
 ...llDitherers_CalliphoraPartial_Bayer4x4.png |   4 +-
 ...llDitherers_CalliphoraPartial_Bayer8x8.png |   4 +-
 ...Ditherers_CalliphoraPartial_Ordered3x3.png |   4 +-
 ...e1962_Rgba32_issue1962_tiniest_gif_1st.png |   4 +-
 ...2012BadMinCode_Rgba32_issue2012_drona1.png |   4 +-
 ...zed_Encode_Artifacts_Rgba32_issue_2469.png |   4 +-
 ...antized_Encode_Alpha_Rgba32_Issue_2668.png |   4 +-
 ...InBox_Bike_OctreeQuantizer_ErrorDither.png |   4 +-
 ...ionInBox_Bike_OctreeQuantizer_NoDither.png |   4 +-
 ...Box_Bike_OctreeQuantizer_OrderedDither.png |   4 +-
 ...ke_WebSafePaletteQuantizer_ErrorDither.png |   4 +-
 ..._Bike_WebSafePaletteQuantizer_NoDither.png |   4 +-
 ..._WebSafePaletteQuantizer_OrderedDither.png |   4 +-
 ...ike_WernerPaletteQuantizer_ErrorDither.png |   4 +-
 ...x_Bike_WernerPaletteQuantizer_NoDither.png |   4 +-
 ...e_WernerPaletteQuantizer_OrderedDither.png |   4 +-
 ...tionInBox_Bike_WuQuantizer_ErrorDither.png |   4 +-
 ...onInBox_Bike_WuQuantizer_OrderedDither.png |   4 +-
 ...oraPartial_OctreeQuantizer_ErrorDither.png |   4 +-
 ...iphoraPartial_OctreeQuantizer_NoDither.png |   4 +-
 ...aPartial_OctreeQuantizer_OrderedDither.png |   4 +-
 ...al_WebSafePaletteQuantizer_ErrorDither.png |   4 +-
 ...rtial_WebSafePaletteQuantizer_NoDither.png |   4 +-
 ..._WebSafePaletteQuantizer_OrderedDither.png |   4 +-
 ...ial_WernerPaletteQuantizer_ErrorDither.png |   4 +-
 ...artial_WernerPaletteQuantizer_NoDither.png |   4 +-
 ...l_WernerPaletteQuantizer_OrderedDither.png |   4 +-
 ...liphoraPartial_WuQuantizer_ErrorDither.png |   4 +-
 ...phoraPartial_WuQuantizer_OrderedDither.png |   4 +-
 ...david_OctreeQuantizer_ErrorDither_0.25.png |   4 +-
 ..._david_OctreeQuantizer_ErrorDither_0.5.png |   4 +-
 ...david_OctreeQuantizer_ErrorDither_0.75.png |   4 +-
 ...le_david_OctreeQuantizer_ErrorDither_0.png |   4 +-
 ...le_david_OctreeQuantizer_ErrorDither_1.png |   4 +-
 ...vid_OctreeQuantizer_OrderedDither_0.25.png |   4 +-
 ...avid_OctreeQuantizer_OrderedDither_0.5.png |   4 +-
 ...vid_OctreeQuantizer_OrderedDither_0.75.png |   4 +-
 ..._david_OctreeQuantizer_OrderedDither_0.png |   4 +-
 ..._david_OctreeQuantizer_OrderedDither_1.png |   4 +-
 ...bSafePaletteQuantizer_ErrorDither_0.25.png |   4 +-
 ...ebSafePaletteQuantizer_ErrorDither_0.5.png |   4 +-
 ...bSafePaletteQuantizer_ErrorDither_0.75.png |   4 +-
 ..._WebSafePaletteQuantizer_ErrorDither_0.png |   4 +-
 ..._WebSafePaletteQuantizer_ErrorDither_1.png |   4 +-
 ...afePaletteQuantizer_OrderedDither_0.25.png |   4 +-
 ...SafePaletteQuantizer_OrderedDither_0.5.png |   4 +-
 ...afePaletteQuantizer_OrderedDither_0.75.png |   4 +-
 ...ebSafePaletteQuantizer_OrderedDither_0.png |   4 +-
 ...ebSafePaletteQuantizer_OrderedDither_1.png |   4 +-
 ...ernerPaletteQuantizer_ErrorDither_0.25.png |   4 +-
 ...WernerPaletteQuantizer_ErrorDither_0.5.png |   4 +-
 ...ernerPaletteQuantizer_ErrorDither_0.75.png |   4 +-
 ...d_WernerPaletteQuantizer_ErrorDither_0.png |   4 +-
 ...d_WernerPaletteQuantizer_ErrorDither_1.png |   4 +-
 ...nerPaletteQuantizer_OrderedDither_0.25.png |   4 +-
 ...rnerPaletteQuantizer_OrderedDither_0.5.png |   4 +-
 ...nerPaletteQuantizer_OrderedDither_0.75.png |   4 +-
 ...WernerPaletteQuantizer_OrderedDither_0.png |   4 +-
 ...WernerPaletteQuantizer_OrderedDither_1.png |   4 +-
 ...ale_david_WuQuantizer_ErrorDither_0.25.png |   4 +-
 ...cale_david_WuQuantizer_ErrorDither_0.5.png |   4 +-
 ...ale_david_WuQuantizer_ErrorDither_0.75.png |   4 +-
 ...gScale_david_WuQuantizer_ErrorDither_0.png |   4 +-
 ...gScale_david_WuQuantizer_ErrorDither_1.png |   4 +-
 ...e_david_WuQuantizer_OrderedDither_0.25.png |   4 +-
 ...le_david_WuQuantizer_OrderedDither_0.5.png |   4 +-
 ...e_david_WuQuantizer_OrderedDither_0.75.png |   4 +-
 ...cale_david_WuQuantizer_OrderedDither_0.png |   4 +-
 ...cale_david_WuQuantizer_OrderedDither_1.png |   4 +-
 ...ation_Bike_OctreeQuantizer_ErrorDither.png |   4 +-
 ...tization_Bike_OctreeQuantizer_NoDither.png |   4 +-
 ...ion_Bike_OctreeQuantizer_OrderedDither.png |   4 +-
 ...ke_WebSafePaletteQuantizer_ErrorDither.png |   4 +-
 ..._Bike_WebSafePaletteQuantizer_NoDither.png |   4 +-
 ..._WebSafePaletteQuantizer_OrderedDither.png |   4 +-
 ...ike_WernerPaletteQuantizer_ErrorDither.png |   4 +-
 ...n_Bike_WernerPaletteQuantizer_NoDither.png |   4 +-
 ...e_WernerPaletteQuantizer_OrderedDither.png |   4 +-
 ...ntization_Bike_WuQuantizer_ErrorDither.png |   4 +-
 ...Quantization_Bike_WuQuantizer_NoDither.png |   4 +-
 ...ization_Bike_WuQuantizer_OrderedDither.png |   4 +-
 ...oraPartial_OctreeQuantizer_ErrorDither.png |   4 +-
 ...iphoraPartial_OctreeQuantizer_NoDither.png |   4 +-
 ...aPartial_OctreeQuantizer_OrderedDither.png |   4 +-
 ...al_WebSafePaletteQuantizer_ErrorDither.png |   4 +-
 ...rtial_WebSafePaletteQuantizer_NoDither.png |   4 +-
 ..._WebSafePaletteQuantizer_OrderedDither.png |   4 +-
 ...ial_WernerPaletteQuantizer_ErrorDither.png |   4 +-
 ...artial_WernerPaletteQuantizer_NoDither.png |   4 +-
 ...l_WernerPaletteQuantizer_OrderedDither.png |   4 +-
 ...liphoraPartial_WuQuantizer_ErrorDither.png |   4 +-
 ...CalliphoraPartial_WuQuantizer_NoDither.png |   4 +-
 ...phoraPartial_WuQuantizer_OrderedDither.png |   4 +-
 tests/Images/Input/Gif/issues/issue_2866.gif  |   3 +
 .../Images/Input/Png/issues/issue_2469-i.png  |   3 +
 tests/Images/Input/Webp/issues/Issue2866.webp |   3 +
 177 files changed, 2120 insertions(+), 861 deletions(-)
 create mode 100644 src/ImageSharp/Common/InlineArray.cs
 create mode 100644 src/ImageSharp/Common/InlineArray.tt
 create mode 100644 tests/Images/Input/Gif/issues/issue_2866.gif
 create mode 100644 tests/Images/Input/Png/issues/issue_2469-i.png
 create mode 100644 tests/Images/Input/Webp/issues/Issue2866.webp

diff --git a/src/ImageSharp/Common/InlineArray.cs b/src/ImageSharp/Common/InlineArray.cs
new file mode 100644
index 0000000000..358121d0a4
--- /dev/null
+++ b/src/ImageSharp/Common/InlineArray.cs
@@ -0,0 +1,29 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+// <auto-generated />
+
+using System;
+using System.Runtime.CompilerServices;
+
+namespace SixLabors.ImageSharp;
+
+/// <summary>
+/// Represents a safe, fixed sized buffer of 4 elements.
+/// </summary>
+[InlineArray(4)]
+internal struct InlineArray4<T>
+{
+    private T t;
+}
+
+/// <summary>
+/// Represents a safe, fixed sized buffer of 16 elements.
+/// </summary>
+[InlineArray(16)]
+internal struct InlineArray16<T>
+{
+    private T t;
+}
+
+
diff --git a/src/ImageSharp/Common/InlineArray.tt b/src/ImageSharp/Common/InlineArray.tt
new file mode 100644
index 0000000000..fae6ab2279
--- /dev/null
+++ b/src/ImageSharp/Common/InlineArray.tt
@@ -0,0 +1,38 @@
+<#@ template debug="false" hostspecific="false" language="C#" #>
+<#@ assembly name="System.Core" #>
+<#@ import namespace="System.Linq" #>
+<#@ import namespace="System.Text" #>
+<#@ import namespace="System.Collections.Generic" #>
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+// <auto-generated />
+
+using System;
+using System.Runtime.CompilerServices;
+
+namespace SixLabors.ImageSharp;
+
+<#GenerateInlineArrays();#>
+
+<#+
+private static int[] Lengths = new int[] {4, 16 };
+
+void GenerateInlineArrays()
+{
+    foreach (int length in Lengths)
+    {
+#>
+/// <summary>
+/// Represents a safe, fixed sized buffer of <#=length#> elements.
+/// </summary>
+[InlineArray(<#=length#>)]
+internal struct InlineArray<#=length#><T>
+{
+    private T t;
+}
+
+<#+
+    }
+}
+#>
diff --git a/src/ImageSharp/Formats/Bmp/BmpMetadata.cs b/src/ImageSharp/Formats/Bmp/BmpMetadata.cs
index d0c60421c4..1dac74ba3a 100644
--- a/src/ImageSharp/Formats/Bmp/BmpMetadata.cs
+++ b/src/ImageSharp/Formats/Bmp/BmpMetadata.cs
@@ -158,6 +158,5 @@ public FormatConnectingMetadata ToFormatConnectingMetadata()
     /// <inheritdoc/>
     public void AfterImageApply<TPixel>(Image<TPixel> destination)
         where TPixel : unmanaged, IPixel<TPixel>
-    {
-    }
+        => this.ColorTable = null;
 }
diff --git a/src/ImageSharp/Formats/Cur/CurFrameMetadata.cs b/src/ImageSharp/Formats/Cur/CurFrameMetadata.cs
index 01b7fbce08..f1ebec72f5 100644
--- a/src/ImageSharp/Formats/Cur/CurFrameMetadata.cs
+++ b/src/ImageSharp/Formats/Cur/CurFrameMetadata.cs
@@ -126,6 +126,7 @@ public void AfterFrameApply<TPixel>(ImageFrame<TPixel> source, ImageFrame<TPixel
         float ratioY = destination.Height / (float)source.Height;
         this.EncodingWidth = ScaleEncodingDimension(this.EncodingWidth, destination.Width, ratioX);
         this.EncodingHeight = ScaleEncodingDimension(this.EncodingHeight, destination.Height, ratioY);
+        this.ColorTable = null;
     }
 
     /// <inheritdoc/>
diff --git a/src/ImageSharp/Formats/Cur/CurMetadata.cs b/src/ImageSharp/Formats/Cur/CurMetadata.cs
index 19de7f434d..5c725e2916 100644
--- a/src/ImageSharp/Formats/Cur/CurMetadata.cs
+++ b/src/ImageSharp/Formats/Cur/CurMetadata.cs
@@ -152,8 +152,7 @@ public FormatConnectingMetadata ToFormatConnectingMetadata()
     /// <inheritdoc/>
     public void AfterImageApply<TPixel>(Image<TPixel> destination)
         where TPixel : unmanaged, IPixel<TPixel>
-    {
-    }
+        => this.ColorTable = null;
 
     /// <inheritdoc/>
     IDeepCloneable IDeepCloneable.DeepClone() => this.DeepClone();
diff --git a/src/ImageSharp/Formats/EncodingUtilities.cs b/src/ImageSharp/Formats/EncodingUtilities.cs
index a979fdf6fa..db951b1c33 100644
--- a/src/ImageSharp/Formats/EncodingUtilities.cs
+++ b/src/ImageSharp/Formats/EncodingUtilities.cs
@@ -3,6 +3,7 @@
 
 using System.Buffers;
 using System.Numerics;
+using System.Runtime.CompilerServices;
 using System.Runtime.Intrinsics;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;
@@ -24,13 +25,29 @@ public static bool ShouldClearTransparentPixels<TPixel>(TransparentColorMode mod
     /// to better compression in some cases.
     /// </summary>
     /// <typeparam name="TPixel">The type of the pixel.</typeparam>
-    /// <param name="clone">The cloned <see cref="ImageFrame{TPixel}"/> where the transparent pixels will be changed.</param>
+    /// <param name="frame">The <see cref="ImageFrame{TPixel}"/> where the transparent pixels will be changed.</param>
     /// <param name="color">The color to replace transparent pixels with.</param>
-    public static void ClearTransparentPixels<TPixel>(ImageFrame<TPixel> clone, Color color)
+    public static void ClearTransparentPixels<TPixel>(ImageFrame<TPixel> frame, Color color)
+        where TPixel : unmanaged, IPixel<TPixel>
+        => ClearTransparentPixels(frame.Configuration, frame.PixelBuffer, color);
+
+    /// <summary>
+    /// Convert transparent pixels, to pixels represented by <paramref name="color"/>, which can yield
+    /// to better compression in some cases.
+    /// </summary>
+    /// <typeparam name="TPixel">The type of the pixel.</typeparam>
+    /// <param name="configuration">The configuration.</param>
+    /// <param name="buffer">The  <see cref="Buffer2D{TPixel}"/> where the transparent pixels will be changed.</param>
+    /// <param name="color">The color to replace transparent pixels with.</param>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static void ClearTransparentPixels<TPixel>(
+        Configuration configuration,
+        Buffer2D<TPixel> buffer,
+        Color color)
         where TPixel : unmanaged, IPixel<TPixel>
     {
-        Buffer2DRegion<TPixel> buffer = clone.PixelBuffer.GetRegion();
-        ClearTransparentPixels(clone.Configuration, ref buffer, color);
+        Buffer2DRegion<TPixel> region = buffer.GetRegion();
+        ClearTransparentPixels(configuration, in region, color);
     }
 
     /// <summary>
@@ -39,29 +56,27 @@ public static void ClearTransparentPixels<TPixel>(ImageFrame<TPixel> clone, Colo
     /// </summary>
     /// <typeparam name="TPixel">The type of the pixel.</typeparam>
     /// <param name="configuration">The configuration.</param>
-    /// <param name="clone">The cloned <see cref="Buffer2DRegion{T}"/> where the transparent pixels will be changed.</param>
+    /// <param name="region">The <see cref="Buffer2DRegion{T}"/> where the transparent pixels will be changed.</param>
     /// <param name="color">The color to replace transparent pixels with.</param>
     public static void ClearTransparentPixels<TPixel>(
         Configuration configuration,
-        ref Buffer2DRegion<TPixel> clone,
+        in Buffer2DRegion<TPixel> region,
         Color color)
         where TPixel : unmanaged, IPixel<TPixel>
     {
-        using IMemoryOwner<Vector4> vectors = configuration.MemoryAllocator.Allocate<Vector4>(clone.Width);
+        using IMemoryOwner<Vector4> vectors = configuration.MemoryAllocator.Allocate<Vector4>(region.Width);
         Span<Vector4> vectorsSpan = vectors.GetSpan();
         Vector4 replacement = color.ToScaledVector4();
-        for (int y = 0; y < clone.Height; y++)
+        for (int y = 0; y < region.Height; y++)
         {
-            Span<TPixel> span = clone.DangerousGetRowSpan(y);
+            Span<TPixel> span = region.DangerousGetRowSpan(y);
             PixelOperations<TPixel>.Instance.ToVector4(configuration, span, vectorsSpan, PixelConversionModifiers.Scale);
             ClearTransparentPixelRow(vectorsSpan, replacement);
             PixelOperations<TPixel>.Instance.FromVector4Destructive(configuration, vectorsSpan, span, PixelConversionModifiers.Scale);
         }
     }
 
-    private static void ClearTransparentPixelRow(
-        Span<Vector4> vectorsSpan,
-        Vector4 replacement)
+    private static void ClearTransparentPixelRow(Span<Vector4> vectorsSpan, Vector4 replacement)
     {
         if (Vector128.IsHardwareAccelerated)
         {
diff --git a/src/ImageSharp/Formats/Gif/GifDecoderCore.cs b/src/ImageSharp/Formats/Gif/GifDecoderCore.cs
index e18166c4b8..e9012436e9 100644
--- a/src/ImageSharp/Formats/Gif/GifDecoderCore.cs
+++ b/src/ImageSharp/Formats/Gif/GifDecoderCore.cs
@@ -89,6 +89,11 @@ internal sealed class GifDecoderCore : ImageDecoderCore
     /// </summary>
     private GifMetadata? gifMetadata;
 
+    /// <summary>
+    /// The background color used to fill the frame.
+    /// </summary>
+    private Color backgroundColor;
+
     /// <summary>
     /// Initializes a new instance of the <see cref="GifDecoderCore"/> class.
     /// </summary>
@@ -108,9 +113,13 @@ protected override Image<TPixel> Decode<TPixel>(BufferedReadStream stream, Cance
         uint frameCount = 0;
         Image<TPixel>? image = null;
         ImageFrame<TPixel>? previousFrame = null;
+        FrameDisposalMode? previousDisposalMode = null;
+        bool globalColorTableUsed = false;
+
         try
         {
             this.ReadLogicalScreenDescriptorAndGlobalColorTable(stream);
+            TPixel backgroundPixel = this.backgroundColor.ToPixel<TPixel>();
 
             // Loop though the respective gif parts and read the data.
             int nextFlag = stream.ReadByte();
@@ -123,7 +132,7 @@ protected override Image<TPixel> Decode<TPixel>(BufferedReadStream stream, Cance
                         break;
                     }
 
-                    this.ReadFrame(stream, ref image, ref previousFrame);
+                    globalColorTableUsed |= this.ReadFrame(stream, ref image, ref previousFrame, ref previousDisposalMode, backgroundPixel);
 
                     // Reset per-frame state.
                     this.imageDescriptor = default;
@@ -158,6 +167,13 @@ protected override Image<TPixel> Decode<TPixel>(BufferedReadStream stream, Cance
                     break;
                 }
             }
+
+            // We cannot always trust the global GIF palette has actually been used.
+            // https://github.com/SixLabors/ImageSharp/issues/2866
+            if (!globalColorTableUsed)
+            {
+                this.gifMetadata.ColorTableMode = FrameColorTableMode.Local;
+            }
         }
         finally
         {
@@ -179,6 +195,8 @@ protected override ImageInfo Identify(BufferedReadStream stream, CancellationTok
         uint frameCount = 0;
         ImageFrameMetadata? previousFrame = null;
         List<ImageFrameMetadata> framesMetadata = [];
+        bool globalColorTableUsed = false;
+
         try
         {
             this.ReadLogicalScreenDescriptorAndGlobalColorTable(stream);
@@ -194,7 +212,7 @@ protected override ImageInfo Identify(BufferedReadStream stream, CancellationTok
                         break;
                     }
 
-                    this.ReadFrameMetadata(stream, framesMetadata, ref previousFrame);
+                    globalColorTableUsed |= this.ReadFrameMetadata(stream, framesMetadata, ref previousFrame);
 
                     // Reset per-frame state.
                     this.imageDescriptor = default;
@@ -229,6 +247,13 @@ protected override ImageInfo Identify(BufferedReadStream stream, CancellationTok
                     break;
                 }
             }
+
+            // We cannot always trust the global GIF palette has actually been used.
+            // https://github.com/SixLabors/ImageSharp/issues/2866
+            if (!globalColorTableUsed)
+            {
+                this.gifMetadata.ColorTableMode = FrameColorTableMode.Local;
+            }
         }
         finally
         {
@@ -416,7 +441,15 @@ private void ReadComments(BufferedReadStream stream)
     /// <param name="stream">The <see cref="BufferedReadStream"/> containing image data.</param>
     /// <param name="image">The image to decode the information to.</param>
     /// <param name="previousFrame">The previous frame.</param>
-    private void ReadFrame<TPixel>(BufferedReadStream stream, ref Image<TPixel>? image, ref ImageFrame<TPixel>? previousFrame)
+    /// <param name="previousDisposalMode">The previous frame disposal mode.</param>
+    /// <param name="backgroundPixel">The background color pixel.</param>
+    /// <returns>Whether the frame has a global color table.</returns>
+    private bool ReadFrame<TPixel>(
+        BufferedReadStream stream,
+        ref Image<TPixel>? image,
+        ref ImageFrame<TPixel>? previousFrame,
+        ref FrameDisposalMode? previousDisposalMode,
+        TPixel backgroundPixel)
         where TPixel : unmanaged, IPixel<TPixel>
     {
         this.ReadImageDescriptor(stream);
@@ -438,10 +471,12 @@ private void ReadFrame<TPixel>(BufferedReadStream stream, ref Image<TPixel>? ima
         }
 
         ReadOnlySpan<Rgb24> colorTable = MemoryMarshal.Cast<byte, Rgb24>(rawColorTable);
-        this.ReadFrameColors(stream, ref image, ref previousFrame, colorTable);
+        this.ReadFrameColors(stream, ref image, ref previousFrame, ref previousDisposalMode, colorTable, backgroundPixel);
 
         // Skip any remaining blocks
         SkipBlock(stream);
+
+        return !hasLocalColorTable;
     }
 
     /// <summary>
@@ -451,46 +486,36 @@ private void ReadFrame<TPixel>(BufferedReadStream stream, ref Image<TPixel>? ima
     /// <param name="stream">The <see cref="BufferedReadStream"/> containing image data.</param>
     /// <param name="image">The image to decode the information to.</param>
     /// <param name="previousFrame">The previous frame.</param>
+    /// <param name="previousDisposalMode">The previous frame disposal mode.</param>
     /// <param name="colorTable">The color table containing the available colors.</param>
+    /// <param name="backgroundPixel">The background color pixel.</param>
     private void ReadFrameColors<TPixel>(
         BufferedReadStream stream,
         ref Image<TPixel>? image,
         ref ImageFrame<TPixel>? previousFrame,
-        ReadOnlySpan<Rgb24> colorTable)
+        ref FrameDisposalMode? previousDisposalMode,
+        ReadOnlySpan<Rgb24> colorTable,
+        TPixel backgroundPixel)
         where TPixel : unmanaged, IPixel<TPixel>
     {
         GifImageDescriptor descriptor = this.imageDescriptor;
         int imageWidth = this.logicalScreenDescriptor.Width;
         int imageHeight = this.logicalScreenDescriptor.Height;
         bool transFlag = this.graphicsControlExtension.TransparencyFlag;
-
-        ImageFrame<TPixel>? prevFrame = null;
-        ImageFrame<TPixel>? currentFrame = null;
-        ImageFrame<TPixel> imageFrame;
+        FrameDisposalMode disposalMethod = this.graphicsControlExtension.DisposalMethod;
+        ImageFrame<TPixel> currentFrame;
 
         if (previousFrame is null)
         {
-            if (!transFlag)
-            {
-                image = new Image<TPixel>(this.configuration, imageWidth, imageHeight, Color.Black.ToPixel<TPixel>(), this.metadata);
-            }
-            else
-            {
-                // This initializes the image to become fully transparent because the alpha channel is zero.
-                image = new Image<TPixel>(this.configuration, imageWidth, imageHeight, this.metadata);
-            }
+            image = transFlag
+                ? new Image<TPixel>(this.configuration, imageWidth, imageHeight, this.metadata)
+                : new Image<TPixel>(this.configuration, imageWidth, imageHeight, backgroundPixel, this.metadata);
 
             this.SetFrameMetadata(image.Frames.RootFrame.Metadata);
-
-            imageFrame = image.Frames.RootFrame;
+            currentFrame = image.Frames.RootFrame;
         }
         else
         {
-            if (this.graphicsControlExtension.DisposalMethod == FrameDisposalMode.RestoreToPrevious)
-            {
-                prevFrame = previousFrame;
-            }
-
             // We create a clone of the frame and add it.
             // We will overpaint the difference of pixels on the current frame to create a complete image.
             // This ensures that we have enough pixel data to process without distortion. #2450
@@ -498,9 +523,19 @@ private void ReadFrameColors<TPixel>(
 
             this.SetFrameMetadata(currentFrame.Metadata);
 
-            imageFrame = currentFrame;
+            if (previousDisposalMode == FrameDisposalMode.RestoreToBackground)
+            {
+                this.RestoreToBackground(currentFrame, backgroundPixel, transFlag);
+            }
+        }
+
+        Rectangle interest = Rectangle.Intersect(image.Bounds, new(descriptor.Left, descriptor.Top, descriptor.Width, descriptor.Height));
+        previousFrame = currentFrame;
+        previousDisposalMode = disposalMethod;
 
-            this.RestoreToBackground(imageFrame);
+        if (disposalMethod == FrameDisposalMode.RestoreToBackground)
+        {
+            this.restoreArea = interest;
         }
 
         if (colorTable.Length == 0)
@@ -568,7 +603,7 @@ private void ReadFrameColors<TPixel>(
 
                 // #403 The left + width value can be larger than the image width
                 int maxX = Math.Min(descriptorRight, imageWidth);
-                Span<TPixel> row = imageFrame.PixelBuffer.DangerousGetRowSpan(writeY);
+                Span<TPixel> row = currentFrame.PixelBuffer.DangerousGetRowSpan(writeY);
 
                 // Take the descriptorLeft..maxX slice of the row, so the loop can be simplified.
                 row = row[descriptorLeft..maxX];
@@ -599,19 +634,6 @@ private void ReadFrameColors<TPixel>(
                 }
             }
         }
-
-        if (prevFrame != null)
-        {
-            previousFrame = prevFrame;
-            return;
-        }
-
-        previousFrame = currentFrame ?? image.Frames.RootFrame;
-
-        if (this.graphicsControlExtension.DisposalMethod == FrameDisposalMode.RestoreToBackground)
-        {
-            this.restoreArea = new Rectangle(descriptor.Left, descriptor.Top, descriptor.Width, descriptor.Height);
-        }
     }
 
     /// <summary>
@@ -620,7 +642,8 @@ private void ReadFrameColors<TPixel>(
     /// <param name="stream">The <see cref="BufferedReadStream"/> containing image data.</param>
     /// <param name="frameMetadata">The collection of frame metadata.</param>
     /// <param name="previousFrame">The previous frame metadata.</param>
-    private void ReadFrameMetadata(BufferedReadStream stream, List<ImageFrameMetadata> frameMetadata, ref ImageFrameMetadata? previousFrame)
+    /// <returns>Whether the frame has a global color table.</returns>
+    private bool ReadFrameMetadata(BufferedReadStream stream, List<ImageFrameMetadata> frameMetadata, ref ImageFrameMetadata? previousFrame)
     {
         this.ReadImageDescriptor(stream);
 
@@ -632,6 +655,11 @@ private void ReadFrameMetadata(BufferedReadStream stream, List<ImageFrameMetadat
             this.currentLocalColorTable ??= this.configuration.MemoryAllocator.Allocate<byte>(768, AllocationOptions.Clean);
             stream.Read(this.currentLocalColorTable.GetSpan()[..length]);
         }
+        else
+        {
+            this.currentLocalColorTable = null;
+            this.currentLocalColorTableSize = 0;
+        }
 
         // Skip the frame indices. Pixels length + mincode size.
         // The gif format does not tell us the length of the compressed data beforehand.
@@ -649,6 +677,8 @@ private void ReadFrameMetadata(BufferedReadStream stream, List<ImageFrameMetadat
 
         // Skip any remaining blocks
         SkipBlock(stream);
+
+        return !this.imageDescriptor.LocalColorTableFlag;
     }
 
     /// <summary>
@@ -656,7 +686,9 @@ private void ReadFrameMetadata(BufferedReadStream stream, List<ImageFrameMetadat
     /// </summary>
     /// <typeparam name="TPixel">The pixel format.</typeparam>
     /// <param name="frame">The frame.</param>
-    private void RestoreToBackground<TPixel>(ImageFrame<TPixel> frame)
+    /// <param name="background">The background color.</param>
+    /// <param name="transparent">Whether the background is transparent.</param>
+    private void RestoreToBackground<TPixel>(ImageFrame<TPixel> frame, TPixel background, bool transparent)
         where TPixel : unmanaged, IPixel<TPixel>
     {
         if (this.restoreArea is null)
@@ -666,7 +698,14 @@ private void RestoreToBackground<TPixel>(ImageFrame<TPixel> frame)
 
         Rectangle interest = Rectangle.Intersect(frame.Bounds, this.restoreArea.Value);
         Buffer2DRegion<TPixel> pixelRegion = frame.PixelBuffer.GetRegion(interest);
-        pixelRegion.Clear();
+        if (transparent)
+        {
+            pixelRegion.Clear();
+        }
+        else
+        {
+            pixelRegion.Fill(background);
+        }
 
         this.restoreArea = null;
     }
@@ -775,7 +814,19 @@ private void ReadLogicalScreenDescriptorAndGlobalColorTable(BufferedReadStream s
             }
         }
 
-        this.gifMetadata.BackgroundColorIndex = this.logicalScreenDescriptor.BackgroundColorIndex;
+        // If the global color table is present, we can set the background color
+        // otherwise we default to transparent to match browser behavior.
+        ReadOnlyMemory<Color>? table = this.gifMetadata.GlobalColorTable;
+        byte index = this.logicalScreenDescriptor.BackgroundColorIndex;
+        if (table is not null && index < table.Value.Length)
+        {
+            this.backgroundColor = table.Value.Span[index];
+            this.gifMetadata.BackgroundColorIndex = index;
+        }
+        else
+        {
+            this.backgroundColor = Color.Transparent;
+        }
     }
 
     private unsafe struct ScratchBuffer
diff --git a/src/ImageSharp/Formats/Gif/GifEncoderCore.cs b/src/ImageSharp/Formats/Gif/GifEncoderCore.cs
index 797e825dc4..a4830d7793 100644
--- a/src/ImageSharp/Formats/Gif/GifEncoderCore.cs
+++ b/src/ImageSharp/Formats/Gif/GifEncoderCore.cs
@@ -39,6 +39,11 @@ internal sealed class GifEncoderCore
     /// </summary>
     private IQuantizer? quantizer;
 
+    /// <summary>
+    /// The fallback quantizer to use when no quantizer is provided.
+    /// </summary>
+    private static readonly IQuantizer FallbackQuantizer = KnownQuantizers.Octree;
+
     /// <summary>
     /// Whether the quantizer was supplied via options.
     /// </summary>
@@ -67,6 +72,9 @@ internal sealed class GifEncoderCore
     /// </summary>
     private readonly ushort? repeatCount;
 
+    /// <summary>
+    /// The transparent color mode.
+    /// </summary>
     private readonly TransparentColorMode transparentColorMode;
 
     /// <summary>
@@ -104,14 +112,18 @@ public void Encode<TPixel>(Image<TPixel> image, Stream stream, CancellationToken
         GifMetadata gifMetadata = image.Metadata.CloneGifMetadata();
         this.colorTableMode ??= gifMetadata.ColorTableMode;
         bool useGlobalTable = this.colorTableMode == FrameColorTableMode.Global;
-
-        // Quantize the first image frame returning a palette.
-        IndexedImageFrame<TPixel>? quantized = null;
+        bool useGlobalTableForFirstFrame = useGlobalTable;
 
         // Work out if there is an explicit transparent index set for the frame. We use that to ensure the
         // correct value is set for the background index when quantizing.
         GifFrameMetadata frameMetadata = GetGifFrameMetadata(image.Frames.RootFrame, -1);
+        if (frameMetadata.ColorTableMode == FrameColorTableMode.Local)
+        {
+            useGlobalTableForFirstFrame = false;
+        }
 
+        // Quantize the first image frame returning a palette.
+        IndexedImageFrame<TPixel>? quantized = null;
         if (this.quantizer is null)
         {
             // Is this a gif with color information. If so use that, otherwise use octree.
@@ -121,21 +133,22 @@ public void Encode<TPixel>(Image<TPixel> image, Stream stream, CancellationToken
                 int transparencyIndex = GetTransparentIndex(quantized, frameMetadata);
                 if (transparencyIndex >= 0 || gifMetadata.GlobalColorTable.Value.Length < 256)
                 {
-                    this.quantizer = new PaletteQuantizer(gifMetadata.GlobalColorTable.Value, new() { Dither = null }, transparencyIndex);
+                    this.quantizer = new PaletteQuantizer(gifMetadata.GlobalColorTable.Value, new() { Dither = null });
                 }
                 else
                 {
-                    this.quantizer = KnownQuantizers.Octree;
+                    this.quantizer = FallbackQuantizer;
                 }
             }
             else
             {
-                this.quantizer = KnownQuantizers.Octree;
+                this.quantizer = FallbackQuantizer;
             }
         }
 
         // Quantize the first frame. Checking to see whether we can clear the transparent pixels
         // to allow for a smaller color palette and encoded result.
+        Color background = Color.Transparent;
         using (IQuantizer<TPixel> frameQuantizer = this.quantizer.CreatePixelSpecificQuantizer<TPixel>(this.configuration))
         {
             ImageFrame<TPixel>? clonedFrame = null;
@@ -147,24 +160,40 @@ public void Encode<TPixel>(Image<TPixel> image, Stream stream, CancellationToken
                 clonedFrame = image.Frames.RootFrame.Clone();
 
                 GifFrameMetadata frameMeta = clonedFrame.Metadata.GetGifMetadata();
-                Color background = frameMeta.DisposalMode == FrameDisposalMode.RestoreToBackground
-                    ? this.backgroundColor ?? Color.Transparent
-                    : Color.Transparent;
+                if (frameMeta.DisposalMode == FrameDisposalMode.RestoreToBackground)
+                {
+                    background = this.backgroundColor ?? Color.Transparent;
+                }
 
                 EncodingUtilities.ClearTransparentPixels(clonedFrame, background);
             }
 
             ImageFrame<TPixel> encodingFrame = clonedFrame ?? image.Frames.RootFrame;
 
-            if (useGlobalTable)
+            if (useGlobalTableForFirstFrame)
             {
-                frameQuantizer.BuildPalette(configuration, mode, strategy, image);
-                quantized = frameQuantizer.QuantizeFrame(encodingFrame, image.Bounds);
+                if (useGlobalTable)
+                {
+                    frameQuantizer.BuildPalette(configuration, mode, strategy, image, background);
+                    quantized = frameQuantizer.QuantizeFrame(encodingFrame, image.Bounds);
+                }
+                else
+                {
+                    frameQuantizer.BuildPalette(configuration, mode, strategy, encodingFrame, background);
+                    quantized = frameQuantizer.QuantizeFrame(encodingFrame, encodingFrame.Bounds);
+                }
             }
             else
             {
-                frameQuantizer.BuildPalette(configuration, mode, strategy, encodingFrame);
-                quantized = frameQuantizer.QuantizeFrame(encodingFrame, image.Bounds);
+                quantized = this.QuantizeAdditionalFrameAndUpdateMetadata(
+                    encodingFrame,
+                    encodingFrame.Bounds,
+                    frameMetadata,
+                    true,
+                    default,
+                    false,
+                    frameMetadata.HasTransparency ? frameMetadata.TransparencyIndex : -1,
+                    background);
             }
 
             clonedFrame?.Dispose();
@@ -259,8 +288,8 @@ private void EncodeAdditionalFrames<TPixel>(
             return;
         }
 
-        PaletteQuantizer<TPixel> paletteQuantizer = default;
-        bool hasPaletteQuantizer = false;
+        PaletteQuantizer<TPixel> globalPaletteQuantizer = default;
+        bool hasGlobalPaletteQuantizer = false;
 
         // Store the first frame as a reference for de-duplication comparison.
         ImageFrame<TPixel> previousFrame = image.Frames.RootFrame;
@@ -280,14 +309,13 @@ private void EncodeAdditionalFrames<TPixel>(
                 GifFrameMetadata gifMetadata = GetGifFrameMetadata(currentFrame, globalTransparencyIndex);
                 bool useLocal = this.colorTableMode == FrameColorTableMode.Local || (gifMetadata.ColorTableMode == FrameColorTableMode.Local);
 
-                if (!useLocal && !hasPaletteQuantizer && i > 0)
+                if (!useLocal && !hasGlobalPaletteQuantizer && i > 0)
                 {
                     // The palette quantizer can reuse the same global pixel map across multiple frames since the palette is unchanging.
                     // This allows a reduction of memory usage across multi-frame gifs using a global palette
                     // and also allows use to reuse the cache from previous runs.
-                    int transparencyIndex = gifMetadata.HasTransparency ? gifMetadata.TransparencyIndex : -1;
-                    paletteQuantizer = new(this.configuration, this.quantizer!.Options, globalPalette, transparencyIndex);
-                    hasPaletteQuantizer = true;
+                    globalPaletteQuantizer = new(this.configuration, this.quantizer!.Options, globalPalette);
+                    hasGlobalPaletteQuantizer = true;
                 }
 
                 this.EncodeAdditionalFrame(
@@ -298,7 +326,7 @@ private void EncodeAdditionalFrames<TPixel>(
                     encodingFrame,
                     useLocal,
                     gifMetadata,
-                    paletteQuantizer,
+                    globalPaletteQuantizer,
                     previousDisposalMode);
 
                 previousFrame = currentFrame;
@@ -307,9 +335,9 @@ private void EncodeAdditionalFrames<TPixel>(
         }
         finally
         {
-            if (hasPaletteQuantizer)
+            if (hasGlobalPaletteQuantizer)
             {
-                paletteQuantizer.Dispose();
+                globalPaletteQuantizer.Dispose();
             }
         }
     }
@@ -387,7 +415,8 @@ private void EncodeAdditionalFrame<TPixel>(
                 useLocal,
                 globalPaletteQuantizer,
                 difference,
-                transparencyIndex);
+                transparencyIndex,
+                background);
 
         this.WriteGraphicalControlExtension(metadata, stream);
 
@@ -410,7 +439,8 @@ private IndexedImageFrame<TPixel> QuantizeAdditionalFrameAndUpdateMetadata<TPixe
         bool useLocal,
         PaletteQuantizer<TPixel> globalPaletteQuantizer,
         bool hasDuplicates,
-        int transparencyIndex)
+        int transparencyIndex,
+        Color transparentColor)
         where TPixel : unmanaged, IPixel<TPixel>
     {
         IndexedImageFrame<TPixel> quantized;
@@ -434,14 +464,14 @@ private IndexedImageFrame<TPixel> QuantizeAdditionalFrameAndUpdateMetadata<TPixe
                         transparencyIndex = palette.Length;
                         metadata.TransparencyIndex = ClampIndex(transparencyIndex);
 
-                        PaletteQuantizer quantizer = new(palette, new() { Dither = null }, transparencyIndex);
+                        PaletteQuantizer quantizer = new(palette, new() { Dither = null }, transparencyIndex, transparentColor);
                         using IQuantizer<TPixel> frameQuantizer = quantizer.CreatePixelSpecificQuantizer<TPixel>(this.configuration, quantizer.Options);
                         quantized = frameQuantizer.BuildPaletteAndQuantizeFrame(encodingFrame, bounds);
                     }
                     else
                     {
                         // We must quantize the frame to generate a local color table.
-                        IQuantizer quantizer = this.hasQuantizer ? this.quantizer! : KnownQuantizers.Octree;
+                        IQuantizer quantizer = this.hasQuantizer ? this.quantizer! : FallbackQuantizer;
                         using IQuantizer<TPixel> frameQuantizer = quantizer.CreatePixelSpecificQuantizer<TPixel>(this.configuration, quantizer.Options);
                         quantized = frameQuantizer.BuildPaletteAndQuantizeFrame(encodingFrame, bounds);
 
@@ -454,7 +484,7 @@ private IndexedImageFrame<TPixel> QuantizeAdditionalFrameAndUpdateMetadata<TPixe
                 else
                 {
                     // Just use the local palette.
-                    PaletteQuantizer quantizer = new(palette, new() { Dither = null }, transparencyIndex);
+                    PaletteQuantizer quantizer = new(palette, new() { Dither = null }, transparencyIndex, transparentColor);
                     using IQuantizer<TPixel> frameQuantizer = quantizer.CreatePixelSpecificQuantizer<TPixel>(this.configuration, quantizer.Options);
                     quantized = frameQuantizer.BuildPaletteAndQuantizeFrame(encodingFrame, bounds);
                 }
@@ -462,7 +492,7 @@ private IndexedImageFrame<TPixel> QuantizeAdditionalFrameAndUpdateMetadata<TPixe
             else
             {
                 // We must quantize the frame to generate a local color table.
-                IQuantizer quantizer = this.hasQuantizer ? this.quantizer! : KnownQuantizers.Octree;
+                IQuantizer quantizer = this.hasQuantizer ? this.quantizer! : FallbackQuantizer;
                 using IQuantizer<TPixel> frameQuantizer = quantizer.CreatePixelSpecificQuantizer<TPixel>(this.configuration, quantizer.Options);
                 quantized = frameQuantizer.BuildPaletteAndQuantizeFrame(encodingFrame, bounds);
 
@@ -486,7 +516,8 @@ private IndexedImageFrame<TPixel> QuantizeAdditionalFrameAndUpdateMetadata<TPixe
         else
         {
             // Quantize the image using the global palette.
-            // Individual frames, though using the shared palette, can use a different transparent index to represent transparency.
+            // Individual frames, though using the shared palette, can use a different transparent index
+            // to represent transparency.
 
             // A difference was captured but the metadata does not have transparency.
             if (hasDuplicates && !metadata.HasTransparency)
@@ -496,7 +527,7 @@ private IndexedImageFrame<TPixel> QuantizeAdditionalFrameAndUpdateMetadata<TPixe
                 metadata.TransparencyIndex = ClampIndex(transparencyIndex);
             }
 
-            globalPaletteQuantizer.SetTransparentIndex(transparencyIndex);
+            globalPaletteQuantizer.SetTransparencyIndex(transparencyIndex, transparentColor.ToPixel<TPixel>());
             quantized = globalPaletteQuantizer.QuantizeFrame(encodingFrame, bounds);
         }
 
diff --git a/src/ImageSharp/Formats/Gif/GifFrameMetadata.cs b/src/ImageSharp/Formats/Gif/GifFrameMetadata.cs
index 5fe892c656..92bd114e8f 100644
--- a/src/ImageSharp/Formats/Gif/GifFrameMetadata.cs
+++ b/src/ImageSharp/Formats/Gif/GifFrameMetadata.cs
@@ -129,8 +129,7 @@ public FormatConnectingFrameMetadata ToFormatConnectingFrameMetadata()
     /// <inheritdoc/>
     public void AfterFrameApply<TPixel>(ImageFrame<TPixel> source, ImageFrame<TPixel> destination)
         where TPixel : unmanaged, IPixel<TPixel>
-    {
-    }
+        => this.LocalColorTable = null;
 
     /// <inheritdoc/>
     IDeepCloneable IDeepCloneable.DeepClone() => this.DeepClone();
diff --git a/src/ImageSharp/Formats/Gif/GifMetadata.cs b/src/ImageSharp/Formats/Gif/GifMetadata.cs
index 517609af45..fc6c9ab9a4 100644
--- a/src/ImageSharp/Formats/Gif/GifMetadata.cs
+++ b/src/ImageSharp/Formats/Gif/GifMetadata.cs
@@ -101,7 +101,7 @@ public static GifMetadata FromFormatConnectingMetadata(FormatConnectingMetadata
     /// <inheritdoc/>
     public PixelTypeInfo GetPixelTypeInfo()
     {
-        int bpp = this.GlobalColorTable.HasValue
+        int bpp = this.ColorTableMode == FrameColorTableMode.Global && this.GlobalColorTable.HasValue
             ? Numerics.Clamp(ColorNumerics.GetBitsNeededForColorDepth(this.GlobalColorTable.Value.Length), 1, 8)
             : 8;
 
@@ -115,15 +115,16 @@ public PixelTypeInfo GetPixelTypeInfo()
     /// <inheritdoc/>
     public FormatConnectingMetadata ToFormatConnectingMetadata()
     {
-        Color color = this.GlobalColorTable.HasValue && this.GlobalColorTable.Value.Span.Length > this.BackgroundColorIndex
+        bool global = this.ColorTableMode == FrameColorTableMode.Global;
+        Color color = global && this.GlobalColorTable.HasValue && this.GlobalColorTable.Value.Span.Length > this.BackgroundColorIndex
             ? this.GlobalColorTable.Value.Span[this.BackgroundColorIndex]
             : Color.Transparent;
 
-        return new()
+        return new FormatConnectingMetadata()
         {
             AnimateRootFrame = true,
+            ColorTable = global ? this.GlobalColorTable : null,
             BackgroundColor = color,
-            ColorTable = this.GlobalColorTable,
             ColorTableMode = this.ColorTableMode,
             PixelTypeInfo = this.GetPixelTypeInfo(),
             RepeatCount = this.RepeatCount,
@@ -133,8 +134,7 @@ public FormatConnectingMetadata ToFormatConnectingMetadata()
     /// <inheritdoc/>
     public void AfterImageApply<TPixel>(Image<TPixel> destination)
         where TPixel : unmanaged, IPixel<TPixel>
-    {
-    }
+        => this.GlobalColorTable = null;
 
     /// <inheritdoc/>
     IDeepCloneable IDeepCloneable.DeepClone() => this.DeepClone();
diff --git a/src/ImageSharp/Formats/IFormatFrameMetadata.cs b/src/ImageSharp/Formats/IFormatFrameMetadata.cs
index 20f27d050c..261cc12639 100644
--- a/src/ImageSharp/Formats/IFormatFrameMetadata.cs
+++ b/src/ImageSharp/Formats/IFormatFrameMetadata.cs
@@ -14,7 +14,7 @@ public interface IFormatFrameMetadata : IDeepCloneable
     /// Converts the metadata to a <see cref="FormatConnectingFrameMetadata"/> instance.
     /// </summary>
     /// <returns>The <see cref="FormatConnectingFrameMetadata"/>.</returns>
-    FormatConnectingFrameMetadata ToFormatConnectingFrameMetadata();
+    public FormatConnectingFrameMetadata ToFormatConnectingFrameMetadata();
 
     /// <summary>
     /// This method is called after a process has been applied to the image frame.
@@ -22,7 +22,7 @@ public interface IFormatFrameMetadata : IDeepCloneable
     /// <typeparam name="TPixel">The type of pixel format.</typeparam>
     /// <param name="source">The source image frame.</param>
     /// <param name="destination">The destination image frame.</param>
-    void AfterFrameApply<TPixel>(ImageFrame<TPixel> source, ImageFrame<TPixel> destination)
+    public void AfterFrameApply<TPixel>(ImageFrame<TPixel> source, ImageFrame<TPixel> destination)
         where TPixel : unmanaged, IPixel<TPixel>;
 }
 
@@ -39,6 +39,6 @@ public interface IFormatFrameMetadata<TSelf> : IFormatFrameMetadata, IDeepClonea
     /// <param name="metadata">The <see cref="FormatConnectingFrameMetadata"/>.</param>
     /// <returns>The <typeparamref name="TSelf"/>.</returns>
 #pragma warning disable CA1000 // Do not declare static members on generic types
-    static abstract TSelf FromFormatConnectingFrameMetadata(FormatConnectingFrameMetadata metadata);
+    public static abstract TSelf FromFormatConnectingFrameMetadata(FormatConnectingFrameMetadata metadata);
 #pragma warning restore CA1000 // Do not declare static members on generic types
 }
diff --git a/src/ImageSharp/Formats/IFormatMetadata.cs b/src/ImageSharp/Formats/IFormatMetadata.cs
index a351431c94..3142b465cb 100644
--- a/src/ImageSharp/Formats/IFormatMetadata.cs
+++ b/src/ImageSharp/Formats/IFormatMetadata.cs
@@ -14,20 +14,20 @@ public interface IFormatMetadata : IDeepCloneable
     /// Converts the metadata to a <see cref="PixelTypeInfo"/> instance.
     /// </summary>
     /// <returns>The pixel type info.</returns>
-    PixelTypeInfo GetPixelTypeInfo();
+    public PixelTypeInfo GetPixelTypeInfo();
 
     /// <summary>
     /// Converts the metadata to a <see cref="FormatConnectingMetadata"/> instance.
     /// </summary>
     /// <returns>The <see cref="FormatConnectingMetadata"/>.</returns>
-    FormatConnectingMetadata ToFormatConnectingMetadata();
+    public FormatConnectingMetadata ToFormatConnectingMetadata();
 
     /// <summary>
     /// This method is called after a process has been applied to the image.
     /// </summary>
     /// <typeparam name="TPixel">The type of pixel format.</typeparam>
     /// <param name="destination">The destination image .</param>
-    void AfterImageApply<TPixel>(Image<TPixel> destination)
+    public void AfterImageApply<TPixel>(Image<TPixel> destination)
         where TPixel : unmanaged, IPixel<TPixel>;
 }
 
@@ -44,6 +44,6 @@ public interface IFormatMetadata<TSelf> : IFormatMetadata, IDeepCloneable<TSelf>
     /// <param name="metadata">The <see cref="FormatConnectingMetadata"/>.</param>
     /// <returns>The <typeparamref name="TSelf"/>.</returns>
 #pragma warning disable CA1000 // Do not declare static members on generic types
-    static abstract TSelf FromFormatConnectingMetadata(FormatConnectingMetadata metadata);
+    public static abstract TSelf FromFormatConnectingMetadata(FormatConnectingMetadata metadata);
 #pragma warning restore CA1000 // Do not declare static members on generic types
 }
diff --git a/src/ImageSharp/Formats/IQuantizingImageEncoder.cs b/src/ImageSharp/Formats/IQuantizingImageEncoder.cs
index 5edf6e40e9..1ce2aa0918 100644
--- a/src/ImageSharp/Formats/IQuantizingImageEncoder.cs
+++ b/src/ImageSharp/Formats/IQuantizingImageEncoder.cs
@@ -13,12 +13,12 @@ public interface IQuantizingImageEncoder
     /// <summary>
     /// Gets the quantizer used to generate the color palette.
     /// </summary>
-    IQuantizer? Quantizer { get; }
+    public IQuantizer? Quantizer { get; }
 
     /// <summary>
     /// Gets the <see cref="IPixelSamplingStrategy"/> used for quantization when building color palettes.
     /// </summary>
-    IPixelSamplingStrategy PixelSamplingStrategy { get; }
+    public IPixelSamplingStrategy PixelSamplingStrategy { get; }
 }
 
 /// <summary>
diff --git a/src/ImageSharp/Formats/Ico/IcoFrameMetadata.cs b/src/ImageSharp/Formats/Ico/IcoFrameMetadata.cs
index 62aa705cbe..77096d5241 100644
--- a/src/ImageSharp/Formats/Ico/IcoFrameMetadata.cs
+++ b/src/ImageSharp/Formats/Ico/IcoFrameMetadata.cs
@@ -119,6 +119,7 @@ public void AfterFrameApply<TPixel>(ImageFrame<TPixel> source, ImageFrame<TPixel
         float ratioY = destination.Height / (float)source.Height;
         this.EncodingWidth = ScaleEncodingDimension(this.EncodingWidth, destination.Width, ratioX);
         this.EncodingHeight = ScaleEncodingDimension(this.EncodingHeight, destination.Height, ratioY);
+        this.ColorTable = null;
     }
 
     /// <inheritdoc/>
diff --git a/src/ImageSharp/Formats/Ico/IcoMetadata.cs b/src/ImageSharp/Formats/Ico/IcoMetadata.cs
index a6c2704b31..09c1da1b1a 100644
--- a/src/ImageSharp/Formats/Ico/IcoMetadata.cs
+++ b/src/ImageSharp/Formats/Ico/IcoMetadata.cs
@@ -152,8 +152,7 @@ public FormatConnectingMetadata ToFormatConnectingMetadata()
     /// <inheritdoc/>
     public void AfterImageApply<TPixel>(Image<TPixel> destination)
         where TPixel : unmanaged, IPixel<TPixel>
-    {
-    }
+        => this.ColorTable = null;
 
     /// <inheritdoc/>
     IDeepCloneable IDeepCloneable.DeepClone() => this.DeepClone();
diff --git a/src/ImageSharp/Formats/Png/PngEncoder.cs b/src/ImageSharp/Formats/Png/PngEncoder.cs
index 63e675b505..1032f88529 100644
--- a/src/ImageSharp/Formats/Png/PngEncoder.cs
+++ b/src/ImageSharp/Formats/Png/PngEncoder.cs
@@ -1,8 +1,6 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
-using SixLabors.ImageSharp.Processing.Processors.Quantization;
-
 namespace SixLabors.ImageSharp.Formats.Png;
 
 /// <summary>
@@ -10,16 +8,6 @@ namespace SixLabors.ImageSharp.Formats.Png;
 /// </summary>
 public class PngEncoder : QuantizingAnimatedImageEncoder
 {
-    /// <summary>
-    /// Initializes a new instance of the <see cref="PngEncoder"/> class.
-    /// </summary>
-    public PngEncoder()
-
-        // Hack. TODO: Investigate means to fix/optimize the Wu quantizer.
-        // The Wu quantizer does not handle the default sampling strategy well for some larger images.
-        // It's expensive and the results are not better than the extensive strategy.
-        => this.PixelSamplingStrategy = new ExtensivePixelSamplingStrategy();
-
     /// <summary>
     /// Gets the number of bits per sample or per palette index (not per pixel).
     /// Not all values are allowed for all <see cref="ColorType" /> values.
diff --git a/src/ImageSharp/Formats/Png/PngEncoderCore.cs b/src/ImageSharp/Formats/Png/PngEncoderCore.cs
index ea36d9fe1e..45d7d1270b 100644
--- a/src/ImageSharp/Formats/Png/PngEncoderCore.cs
+++ b/src/ImageSharp/Formats/Png/PngEncoderCore.cs
@@ -3,8 +3,8 @@
 
 using System.Buffers;
 using System.Buffers.Binary;
+using System.Diagnostics.CodeAnalysis;
 using System.IO.Hashing;
-using System.Numerics;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 using System.Runtime.Intrinsics;
@@ -119,18 +119,13 @@ internal sealed class PngEncoderCore : IDisposable
     /// </summary>
     private IQuantizer? quantizer;
 
-    /// <summary>
-    /// Any explicit quantized transparent index provided by the background color.
-    /// </summary>
-    private int derivedTransparencyIndex = -1;
-
     /// <summary>
     /// The default background color of the canvas when animating.
     /// This color may be used to fill the unused space on the canvas around the frames,
     /// as well as the transparent pixels of the first frame.
     /// The background color is also used when a frame disposal mode is <see cref="FrameDisposalMode.RestoreToBackground"/>.
     /// </summary>
-    private readonly Color? backgroundColor;
+    private Color? backgroundColor;
 
     /// <summary>
     /// The number of times any animation is repeated.
@@ -158,7 +153,6 @@ public PngEncoderCore(Configuration configuration, PngEncoder encoder)
         this.memoryAllocator = configuration.MemoryAllocator;
         this.encoder = encoder;
         this.quantizer = encoder.Quantizer;
-        this.backgroundColor = encoder.BackgroundColor;
         this.repeatCount = encoder.RepeatCount;
         this.animateRootFrame = encoder.AnimateRootFrame;
     }
@@ -187,74 +181,92 @@ public void Encode<TPixel>(Image<TPixel> image, Stream stream, CancellationToken
 
         ImageFrame<TPixel>? clonedFrame = null;
         ImageFrame<TPixel> currentFrame = image.Frames.RootFrame;
-        int currentFrameIndex = 0;
+        IndexedImageFrame<TPixel>? quantized = null;
+        PaletteQuantizer<TPixel>? paletteQuantizer = null;
+        Buffer2DRegion<TPixel> currentFrameRegion = currentFrame.PixelBuffer.GetRegion();
 
-        bool clearTransparency = EncodingUtilities.ShouldClearTransparentPixels<TPixel>(this.encoder.TransparentColorMode);
-        if (clearTransparency)
+        try
         {
-            currentFrame = clonedFrame = currentFrame.Clone();
-            EncodingUtilities.ClearTransparentPixels(currentFrame, Color.Transparent);
-        }
+            int currentFrameIndex = 0;
 
-        // Do not move this. We require an accurate bit depth for the header chunk.
-        IndexedImageFrame<TPixel>? quantized = this.CreateQuantizedImageAndUpdateBitDepth(
-            pngMetadata,
-            currentFrame,
-            currentFrame.Bounds,
-            null);
-
-        this.WriteHeaderChunk(stream);
-        this.WriteGammaChunk(stream);
-        this.WriteCicpChunk(stream, metadata);
-        this.WriteColorProfileChunk(stream, metadata);
-        this.WritePaletteChunk(stream, quantized);
-        this.WriteTransparencyChunk(stream, pngMetadata);
-        this.WritePhysicalChunk(stream, metadata);
-        this.WriteExifChunk(stream, metadata);
-        this.WriteXmpChunk(stream, metadata);
-        this.WriteTextChunks(stream, pngMetadata);
+            bool clearTransparency = EncodingUtilities.ShouldClearTransparentPixels<TPixel>(this.encoder.TransparentColorMode);
+            if (clearTransparency)
+            {
+                currentFrame = clonedFrame = currentFrame.Clone();
+                currentFrameRegion = currentFrame.PixelBuffer.GetRegion();
+                EncodingUtilities.ClearTransparentPixels(this.configuration, in currentFrameRegion, this.backgroundColor.Value);
+            }
 
-        if (image.Frames.Count > 1)
-        {
-            this.WriteAnimationControlChunk(
-                stream,
-                (uint)(image.Frames.Count - (pngMetadata.AnimateRootFrame ? 0 : 1)),
-                this.repeatCount ?? pngMetadata.RepeatCount);
-        }
+            // Do not move this. We require an accurate bit depth for the header chunk.
+            quantized = this.CreateQuantizedImageAndUpdateBitDepth(
+                pngMetadata,
+                image,
+                currentFrame,
+                currentFrame.Bounds,
+                null);
+
+            this.WriteHeaderChunk(stream);
+            this.WriteGammaChunk(stream);
+            this.WriteCicpChunk(stream, metadata);
+            this.WriteColorProfileChunk(stream, metadata);
+            this.WritePaletteChunk(stream, quantized);
+            this.WriteTransparencyChunk(stream, pngMetadata);
+            this.WritePhysicalChunk(stream, metadata);
+            this.WriteExifChunk(stream, metadata);
+            this.WriteXmpChunk(stream, metadata);
+            this.WriteTextChunks(stream, pngMetadata);
 
-        // If the first frame isn't animated, write it as usual and skip it when writing animated frames
-        bool userAnimateRootFrame = this.animateRootFrame == true;
-        if ((!userAnimateRootFrame && !pngMetadata.AnimateRootFrame) || image.Frames.Count == 1)
-        {
-            cancellationToken.ThrowIfCancellationRequested();
-            FrameControl frameControl = new((uint)this.width, (uint)this.height);
-            this.WriteDataChunks(frameControl, currentFrame.PixelBuffer.GetRegion(), quantized, stream, false);
-            currentFrameIndex++;
-        }
+            if (image.Frames.Count > 1)
+            {
+                this.WriteAnimationControlChunk(
+                    stream,
+                    (uint)(image.Frames.Count - (pngMetadata.AnimateRootFrame ? 0 : 1)),
+                    this.repeatCount ?? pngMetadata.RepeatCount);
+            }
+
+            // If the first frame isn't animated, write it as usual and skip it when writing animated frames
+            bool userAnimateRootFrame = this.animateRootFrame == true;
+            if ((!userAnimateRootFrame && !pngMetadata.AnimateRootFrame) || image.Frames.Count == 1)
+            {
+                cancellationToken.ThrowIfCancellationRequested();
+                FrameControl frameControl = new((uint)this.width, (uint)this.height);
+                this.WriteDataChunks(in frameControl, in currentFrameRegion, quantized, stream, false);
+                currentFrameIndex++;
+            }
 
-        try
-        {
             if (image.Frames.Count > 1)
             {
                 // Write the first animated frame.
                 currentFrame = image.Frames[currentFrameIndex];
+                currentFrameRegion = currentFrame.PixelBuffer.GetRegion();
+
                 PngFrameMetadata frameMetadata = currentFrame.Metadata.GetPngMetadata();
                 FrameDisposalMode previousDisposal = frameMetadata.DisposalMode;
                 FrameControl frameControl = this.WriteFrameControlChunk(stream, frameMetadata, currentFrame.Bounds, 0);
                 uint sequenceNumber = 1;
                 if (pngMetadata.AnimateRootFrame)
                 {
-                    this.WriteDataChunks(frameControl, currentFrame.PixelBuffer.GetRegion(), quantized, stream, false);
+                    this.WriteDataChunks(in frameControl, in currentFrameRegion, quantized, stream, false);
                 }
                 else
                 {
-                    sequenceNumber += this.WriteDataChunks(frameControl, currentFrame.PixelBuffer.GetRegion(), quantized, stream, true);
+                    sequenceNumber += this.WriteDataChunks(in frameControl, in currentFrameRegion, quantized, stream, true);
                 }
 
                 currentFrameIndex++;
 
                 // Capture the global palette for reuse on subsequent frames.
-                ReadOnlyMemory<TPixel>? previousPalette = quantized?.Palette.ToArray();
+                ReadOnlyMemory<TPixel> previousPalette = quantized?.Palette.ToArray();
+
+                if (!previousPalette.IsEmpty)
+                {
+                    // Use the previously derived global palette and a shared quantizer to
+                    // quantize the subsequent frames. This allows us to cache the color matching resolution.
+                    paletteQuantizer ??= new(
+                        this.configuration,
+                        this.quantizer!.Options,
+                        previousPalette);
+                }
 
                 // Write following frames.
                 ImageFrame<TPixel> previousFrame = image.Frames.RootFrame;
@@ -267,13 +279,16 @@ public void Encode<TPixel>(Image<TPixel> image, Stream stream, CancellationToken
                     cancellationToken.ThrowIfCancellationRequested();
 
                     ImageFrame<TPixel>? prev = previousDisposal == FrameDisposalMode.RestoreToBackground ? null : previousFrame;
+
                     currentFrame = image.Frames[currentFrameIndex];
+                    currentFrameRegion = currentFrame.PixelBuffer.GetRegion();
+
                     ImageFrame<TPixel>? nextFrame = currentFrameIndex < image.Frames.Count - 1 ? image.Frames[currentFrameIndex + 1] : null;
 
                     frameMetadata = currentFrame.Metadata.GetPngMetadata();
                     bool blend = frameMetadata.BlendMode == FrameBlendMode.Over;
                     Color background = frameMetadata.DisposalMode == FrameDisposalMode.RestoreToBackground
-                        ? this.backgroundColor ?? Color.Transparent
+                        ? this.backgroundColor.Value
                         : Color.Transparent;
 
                     (bool difference, Rectangle bounds) =
@@ -296,8 +311,20 @@ public void Encode<TPixel>(Image<TPixel> image, Stream stream, CancellationToken
 
                     // Dispose of previous quantized frame and reassign.
                     quantized?.Dispose();
-                    quantized = this.CreateQuantizedImageAndUpdateBitDepth(pngMetadata, encodingFrame, bounds, previousPalette);
-                    sequenceNumber += this.WriteDataChunks(frameControl, encodingFrame.PixelBuffer.GetRegion(bounds), quantized, stream, true) + 1;
+
+                    quantized = this.CreateQuantizedFrame(
+                        this.encoder,
+                        this.colorType,
+                        this.bitDepth,
+                        pngMetadata,
+                        image,
+                        encodingFrame,
+                        bounds,
+                        paletteQuantizer,
+                        default);
+
+                    Buffer2DRegion<TPixel> encodingFrameRegion = encodingFrame.PixelBuffer.GetRegion(bounds);
+                    sequenceNumber += this.WriteDataChunks(in frameControl, in encodingFrameRegion, quantized, stream, true) + 1;
 
                     previousFrame = currentFrame;
                     previousDisposal = frameMetadata.DisposalMode;
@@ -313,6 +340,7 @@ public void Encode<TPixel>(Image<TPixel> image, Stream stream, CancellationToken
             // Dispose of allocations from final frame.
             clonedFrame?.Dispose();
             quantized?.Dispose();
+            paletteQuantizer?.Dispose();
         }
     }
 
@@ -328,18 +356,35 @@ public void Dispose()
     /// </summary>
     /// <typeparam name="TPixel">The type of the pixel.</typeparam>
     /// <param name="metadata">The image metadata.</param>
-    /// <param name="frame">The frame to quantize.</param>
+    /// <param name="image">The image.</param>
+    /// <param name="frame">The current image frame.</param>
     /// <param name="bounds">The area of interest within the frame.</param>
-    /// <param name="previousPalette">Any previously derived palette.</param>
+    /// <param name="paletteQuantizer">The quantizer containing any previously derived palette.</param>
     /// <returns>The quantized image.</returns>
     private IndexedImageFrame<TPixel>? CreateQuantizedImageAndUpdateBitDepth<TPixel>(
         PngMetadata metadata,
+        Image<TPixel> image,
         ImageFrame<TPixel> frame,
         Rectangle bounds,
-        ReadOnlyMemory<TPixel>? previousPalette)
+        PaletteQuantizer<TPixel>? paletteQuantizer)
         where TPixel : unmanaged, IPixel<TPixel>
     {
-        IndexedImageFrame<TPixel>? quantized = this.CreateQuantizedFrame(this.encoder, this.colorType, this.bitDepth, metadata, frame, bounds, previousPalette);
+        PngFrameMetadata frameMetadata = frame.Metadata.GetPngMetadata();
+        Color background = frameMetadata.DisposalMode == FrameDisposalMode.RestoreToBackground
+            ? this.backgroundColor ?? Color.Transparent
+            : Color.Transparent;
+
+        IndexedImageFrame<TPixel>? quantized = this.CreateQuantizedFrame(
+            this.encoder,
+            this.colorType,
+            this.bitDepth,
+            metadata,
+            image,
+            frame,
+            bounds,
+            paletteQuantizer,
+            background);
+
         this.bitDepth = CalculateBitDepth(this.colorType, this.bitDepth, quantized);
         return quantized;
     }
@@ -1105,7 +1150,7 @@ private FrameControl WriteFrameControlChunk(Stream stream, PngFrameMetadata fram
     /// <param name="quantized">The quantized pixel data. Can be null.</param>
     /// <param name="stream">The stream.</param>
     /// <param name="isFrame">Is writing fdAT or IDAT.</param>
-    private uint WriteDataChunks<TPixel>(FrameControl frameControl, Buffer2DRegion<TPixel> frame, IndexedImageFrame<TPixel>? quantized, Stream stream, bool isFrame)
+    private uint WriteDataChunks<TPixel>(in FrameControl frameControl, in Buffer2DRegion<TPixel> frame, IndexedImageFrame<TPixel>? quantized, Stream stream, bool isFrame)
         where TPixel : unmanaged, IPixel<TPixel>
     {
         byte[] buffer;
@@ -1123,12 +1168,12 @@ private uint WriteDataChunks<TPixel>(FrameControl frameControl, Buffer2DRegion<T
                     }
                     else
                     {
-                        this.EncodeAdam7Pixels(frame, deflateStream);
+                        this.EncodeAdam7Pixels(in frame, deflateStream);
                     }
                 }
                 else
                 {
-                    this.EncodePixels(frame, quantized, deflateStream);
+                    this.EncodePixels(in frame, quantized, deflateStream);
                 }
             }
 
@@ -1196,7 +1241,7 @@ private void AllocateScanlineBuffers(int bytesPerScanline)
     /// <param name="pixels">The image frame pixel buffer.</param>
     /// <param name="quantized">The quantized pixels.</param>
     /// <param name="deflateStream">The deflate stream.</param>
-    private void EncodePixels<TPixel>(Buffer2DRegion<TPixel> pixels, IndexedImageFrame<TPixel>? quantized, ZlibDeflateStream deflateStream)
+    private void EncodePixels<TPixel>(in Buffer2DRegion<TPixel> pixels, IndexedImageFrame<TPixel>? quantized, ZlibDeflateStream deflateStream)
         where TPixel : unmanaged, IPixel<TPixel>
     {
         int bytesPerScanline = this.CalculateScanlineLength(pixels.Width);
@@ -1222,7 +1267,7 @@ private void EncodePixels<TPixel>(Buffer2DRegion<TPixel> pixels, IndexedImageFra
     /// <typeparam name="TPixel">The type of the pixel.</typeparam>
     /// <param name="pixels">The image frame pixel buffer.</param>
     /// <param name="deflateStream">The deflate stream.</param>
-    private void EncodeAdam7Pixels<TPixel>(Buffer2DRegion<TPixel> pixels, ZlibDeflateStream deflateStream)
+    private void EncodeAdam7Pixels<TPixel>(in Buffer2DRegion<TPixel> pixels, ZlibDeflateStream deflateStream)
         where TPixel : unmanaged, IPixel<TPixel>
     {
         for (int pass = 0; pass < 7; pass++)
@@ -1258,7 +1303,7 @@ private void EncodeAdam7Pixels<TPixel>(Buffer2DRegion<TPixel> pixels, ZlibDeflat
                 // Encode data
                 // Note: quantized parameter not used
                 // Note: row parameter not used
-                this.CollectAndFilterPixelRow<TPixel>(block, ref filter, ref attempt, null, -1);
+                this.CollectAndFilterPixelRow(block, ref filter, ref attempt, null, -1);
                 deflateStream.Write(filter);
 
                 this.SwapScanlineBuffers();
@@ -1432,6 +1477,7 @@ private void SwapScanlineBuffers()
     /// <param name="pngMetadata">The PNG metadata.</param>
     /// <param name="use16Bit">if set to <c>true</c> [use16 bit].</param>
     /// <param name="bytesPerPixel">The bytes per pixel.</param>
+    [MemberNotNull(nameof(backgroundColor))]
     private void SanitizeAndSetEncoderOptions<TPixel>(
         PngEncoder encoder,
         PngMetadata pngMetadata,
@@ -1473,6 +1519,7 @@ private void SanitizeAndSetEncoderOptions<TPixel>(
 
         this.interlaceMode = encoder.InterlaceMethod ?? pngMetadata.InterlaceMethod;
         this.chunkFilter = encoder.SkipMetadata ? PngChunkFilter.ExcludeAll : encoder.ChunkFilter ?? PngChunkFilter.None;
+        this.backgroundColor = encoder.BackgroundColor ?? pngMetadata.TransparentColor ?? Color.Transparent;
     }
 
     /// <summary>
@@ -1483,17 +1530,21 @@ private void SanitizeAndSetEncoderOptions<TPixel>(
     /// <param name="colorType">The color type.</param>
     /// <param name="bitDepth">The bits per component.</param>
     /// <param name="metadata">The image metadata.</param>
-    /// <param name="frame">The frame to quantize.</param>
+    /// <param name="image">The image.</param>
+    /// <param name="frame">The current image frame.</param>
     /// <param name="bounds">The frame area of interest.</param>
-    /// <param name="previousPalette">Any previously derived palette.</param>
+    /// <param name="paletteQuantizer">The quantizer containing any previously derived palette.</param>
+    /// <param name="backgroundColor">The background color.</param>
     private IndexedImageFrame<TPixel>? CreateQuantizedFrame<TPixel>(
         QuantizingImageEncoder encoder,
         PngColorType colorType,
         byte bitDepth,
         PngMetadata metadata,
+        Image<TPixel> image,
         ImageFrame<TPixel> frame,
         Rectangle bounds,
-        ReadOnlyMemory<TPixel>? previousPalette)
+        PaletteQuantizer<TPixel>? paletteQuantizer,
+        Color backgroundColor)
         where TPixel : unmanaged, IPixel<TPixel>
     {
         if (colorType is not PngColorType.Palette)
@@ -1501,55 +1552,52 @@ private void SanitizeAndSetEncoderOptions<TPixel>(
             return null;
         }
 
-        if (previousPalette is not null)
+        if (paletteQuantizer.HasValue)
         {
-            // Use the previously derived palette created by quantizing the root frame to quantize the current frame.
-            using PaletteQuantizer<TPixel> paletteQuantizer = new(
-                this.configuration,
-                this.quantizer!.Options,
-                previousPalette.Value,
-                this.derivedTransparencyIndex);
-            paletteQuantizer.BuildPalette(encoder.PixelSamplingStrategy, frame);
-            return paletteQuantizer.QuantizeFrame(frame, bounds);
+            return paletteQuantizer.Value.QuantizeFrame(frame, bounds);
         }
 
         // Use the metadata to determine what quantization depth to use if no quantizer has been set.
         if (this.quantizer is null)
         {
-            if (metadata.ColorTable is not null)
+            if (metadata.ColorTable?.Length > 0)
             {
                 // We can use the color data from the decoded metadata here.
                 // We avoid dithering by default to preserve the original colors.
-                ReadOnlySpan<Color> palette = metadata.ColorTable.Value.Span;
-
-                // Certain operations perform alpha premultiplication, which can cause the color to change so we
-                // must search for the transparency index in the palette.
-                // Transparent pixels are much more likely to be found at the end of a palette.
-                int index = -1;
-                for (int i = palette.Length - 1; i >= 0; i--)
-                {
-                    Vector4 instance = palette[i].ToScaledVector4();
-                    if (instance.W == 0f)
-                    {
-                        index = i;
-                        break;
-                    }
-                }
-
-                this.derivedTransparencyIndex = index;
-
-                this.quantizer = new PaletteQuantizer(metadata.ColorTable.Value, new() { Dither = null }, this.derivedTransparencyIndex);
+                this.quantizer = new PaletteQuantizer(metadata.ColorTable.Value, new() { Dither = null });
             }
             else
             {
-                this.quantizer = new WuQuantizer(new QuantizerOptions { MaxColors = ColorNumerics.GetColorCountForBitDepth(bitDepth) });
+                // Don't use transparency threshold for quantization PNG can handle multiple transparent colors.
+                this.quantizer = new WuQuantizer(new QuantizerOptions { TransparencyThreshold = 0, MaxColors = ColorNumerics.GetColorCountForBitDepth(bitDepth) });
             }
         }
 
         // Create quantized frame returning the palette and set the bit depth.
         using IQuantizer<TPixel> frameQuantizer = this.quantizer.CreatePixelSpecificQuantizer<TPixel>(frame.Configuration);
 
-        frameQuantizer.BuildPalette(encoder.PixelSamplingStrategy, frame);
+        if (image.Frames.Count > 1)
+        {
+            // Encoding animated frames with a global palette requires a transparent pixel in the palette
+            // since we only encode the delta between frames. To ensure that we have a transparent pixel
+            // we create a fake frame with a containing only transparent pixels and add it to the palette.
+            using Buffer2D<TPixel> px = image.Configuration.MemoryAllocator.Allocate2D<TPixel>(Math.Min(256, image.Width), Math.Min(256, image.Height));
+            TPixel backGroundPixel = backgroundColor.ToPixel<TPixel>();
+            for (int i = 0; i < px.Height; i++)
+            {
+                px.DangerousGetRowSpan(i).Fill(backGroundPixel);
+            }
+
+            frameQuantizer.AddPaletteColors(px.GetRegion());
+        }
+
+        frameQuantizer.BuildPalette(
+            this.configuration,
+            encoder.TransparentColorMode,
+            encoder.PixelSamplingStrategy,
+            image,
+            backgroundColor);
+
         return frameQuantizer.QuantizeFrame(frame, bounds);
     }
 
diff --git a/src/ImageSharp/Formats/Png/PngMetadata.cs b/src/ImageSharp/Formats/Png/PngMetadata.cs
index 00cba088cb..bb80438ba0 100644
--- a/src/ImageSharp/Formats/Png/PngMetadata.cs
+++ b/src/ImageSharp/Formats/Png/PngMetadata.cs
@@ -250,8 +250,7 @@ public FormatConnectingMetadata ToFormatConnectingMetadata()
     /// <inheritdoc/>
     public void AfterImageApply<TPixel>(Image<TPixel> destination)
         where TPixel : unmanaged, IPixel<TPixel>
-    {
-    }
+        => this.ColorTable = null;
 
     /// <inheritdoc/>
     IDeepCloneable IDeepCloneable.DeepClone() => this.DeepClone();
diff --git a/src/ImageSharp/Formats/TransparentColorMode.cs b/src/ImageSharp/Formats/TransparentColorMode.cs
index 39986b5024..5b52e5fa76 100644
--- a/src/ImageSharp/Formats/TransparentColorMode.cs
+++ b/src/ImageSharp/Formats/TransparentColorMode.cs
@@ -18,5 +18,5 @@ public enum TransparentColorMode
     /// to fully transparent pixels (all components set to zero),
     /// which may improve compression.
     /// </summary>
-    Clear = 1,
+    Clear = 1
 }
diff --git a/src/ImageSharp/Formats/Webp/BitReader/BitReaderBase.cs b/src/ImageSharp/Formats/Webp/BitReader/BitReaderBase.cs
index 83f9e797ab..2b843cc8f6 100644
--- a/src/ImageSharp/Formats/Webp/BitReader/BitReaderBase.cs
+++ b/src/ImageSharp/Formats/Webp/BitReader/BitReaderBase.cs
@@ -32,7 +32,7 @@ protected BitReaderBase(Stream inputStream, int imageDataSize, MemoryAllocator m
     /// <param name="memoryAllocator">Used for allocating memory during reading data from the stream.</param>
     protected static IMemoryOwner<byte> ReadImageDataFromStream(Stream input, int bytesToRead, MemoryAllocator memoryAllocator)
     {
-        IMemoryOwner<byte> data = memoryAllocator.Allocate<byte>(bytesToRead);
+        IMemoryOwner<byte> data = memoryAllocator.Allocate<byte>(bytesToRead, AllocationOptions.Clean);
         Span<byte> dataSpan = data.Memory.Span;
         input.Read(dataSpan[..bytesToRead], 0, bytesToRead);
 
diff --git a/src/ImageSharp/Formats/Webp/Lossy/Vp8Decoder.cs b/src/ImageSharp/Formats/Webp/Lossy/Vp8Decoder.cs
index b3c5bfaf41..eb4a517511 100644
--- a/src/ImageSharp/Formats/Webp/Lossy/Vp8Decoder.cs
+++ b/src/ImageSharp/Formats/Webp/Lossy/Vp8Decoder.cs
@@ -67,14 +67,14 @@ public Vp8Decoder(Vp8FrameHeader frameHeader, Vp8PictureHeader pictureHeader, Vp
         int extraY = extraRows * this.CacheYStride;
         int extraUv = extraRows / 2 * this.CacheUvStride;
         this.YuvBuffer = memoryAllocator.Allocate<byte>((WebpConstants.Bps * 17) + (WebpConstants.Bps * 9) + extraY);
-        this.CacheY = memoryAllocator.Allocate<byte>((16 * this.CacheYStride) + extraY);
+        this.CacheY = memoryAllocator.Allocate<byte>((16 * this.CacheYStride) + extraY, AllocationOptions.Clean);
         int cacheUvSize = (16 * this.CacheUvStride) + extraUv;
-        this.CacheU = memoryAllocator.Allocate<byte>(cacheUvSize);
-        this.CacheV = memoryAllocator.Allocate<byte>(cacheUvSize);
-        this.TmpYBuffer = memoryAllocator.Allocate<byte>((int)width);
-        this.TmpUBuffer = memoryAllocator.Allocate<byte>((int)width);
-        this.TmpVBuffer = memoryAllocator.Allocate<byte>((int)width);
-        this.Pixels = memoryAllocator.Allocate<byte>((int)(width * height * 4));
+        this.CacheU = memoryAllocator.Allocate<byte>(cacheUvSize, AllocationOptions.Clean);
+        this.CacheV = memoryAllocator.Allocate<byte>(cacheUvSize, AllocationOptions.Clean);
+        this.TmpYBuffer = memoryAllocator.Allocate<byte>((int)width, AllocationOptions.Clean);
+        this.TmpUBuffer = memoryAllocator.Allocate<byte>((int)width, AllocationOptions.Clean);
+        this.TmpVBuffer = memoryAllocator.Allocate<byte>((int)width, AllocationOptions.Clean);
+        this.Pixels = memoryAllocator.Allocate<byte>((int)(width * height * 4), AllocationOptions.Clean);
 
 #if DEBUG
         // Filling those buffers with 205, is only useful for debugging,
diff --git a/src/ImageSharp/Formats/Webp/WebpAnimationDecoder.cs b/src/ImageSharp/Formats/Webp/WebpAnimationDecoder.cs
index b74337ef37..173d9436dd 100644
--- a/src/ImageSharp/Formats/Webp/WebpAnimationDecoder.cs
+++ b/src/ImageSharp/Formats/Webp/WebpAnimationDecoder.cs
@@ -81,16 +81,29 @@ public WebpAnimationDecoder(MemoryAllocator memoryAllocator, Configuration confi
     /// <param name="width">The width of the image.</param>
     /// <param name="height">The height of the image.</param>
     /// <param name="completeDataSize">The size of the image data in bytes.</param>
-    public Image<TPixel> Decode<TPixel>(BufferedReadStream stream, WebpFeatures features, uint width, uint height, uint completeDataSize)
+    public Image<TPixel> Decode<TPixel>(
+        BufferedReadStream stream,
+        WebpFeatures features,
+        uint width,
+        uint height,
+        uint completeDataSize)
         where TPixel : unmanaged, IPixel<TPixel>
     {
         Image<TPixel>? image = null;
         ImageFrame<TPixel>? previousFrame = null;
+        WebpFrameData? prevFrameData = null;
 
         this.metadata = new ImageMetadata();
         this.webpMetadata = this.metadata.GetWebpMetadata();
         this.webpMetadata.RepeatCount = features.AnimationLoopCount;
 
+        Color backgroundColor = this.backgroundColorHandling == BackgroundColorHandling.Ignore
+            ? Color.Transparent
+            : features.AnimationBackgroundColor!.Value;
+
+        this.webpMetadata.BackgroundColor = backgroundColor;
+        TPixel backgroundPixel = backgroundColor.ToPixel<TPixel>();
+
         Span<byte> buffer = stackalloc byte[4];
         uint frameCount = 0;
         int remainingBytes = (int)completeDataSize;
@@ -101,10 +114,16 @@ public Image<TPixel> Decode<TPixel>(BufferedReadStream stream, WebpFeatures feat
             switch (chunkType)
             {
                 case WebpChunkType.FrameData:
-                    Color backgroundColor = this.backgroundColorHandling == BackgroundColorHandling.Ignore
-                        ? Color.FromPixel(new Bgra32(0, 0, 0, 0))
-                        : features.AnimationBackgroundColor!.Value;
-                    uint dataSize = this.ReadFrame(stream, ref image, ref previousFrame, width, height, backgroundColor);
+
+                    uint dataSize = this.ReadFrame(
+                        stream,
+                        ref image,
+                        ref previousFrame,
+                        ref prevFrameData,
+                        width,
+                        height,
+                        backgroundPixel);
+
                     remainingBytes -= (int)dataSize;
                     break;
                 case WebpChunkType.Xmp:
@@ -132,10 +151,18 @@ public Image<TPixel> Decode<TPixel>(BufferedReadStream stream, WebpFeatures feat
     /// <param name="stream">The stream, where the image should be decoded from. Cannot be null.</param>
     /// <param name="image">The image to decode the information to.</param>
     /// <param name="previousFrame">The previous frame.</param>
+    /// <param name="prevFrameData">The previous frame data.</param>
     /// <param name="width">The width of the image.</param>
     /// <param name="height">The height of the image.</param>
     /// <param name="backgroundColor">The default background color of the canvas in.</param>
-    private uint ReadFrame<TPixel>(BufferedReadStream stream, ref Image<TPixel>? image, ref ImageFrame<TPixel>? previousFrame, uint width, uint height, Color backgroundColor)
+    private uint ReadFrame<TPixel>(
+        BufferedReadStream stream,
+        ref Image<TPixel>? image,
+        ref ImageFrame<TPixel>? previousFrame,
+        ref WebpFrameData? prevFrameData,
+        uint width,
+        uint height,
+        TPixel backgroundColor)
         where TPixel : unmanaged, IPixel<TPixel>
     {
         WebpFrameData frameData = WebpFrameData.Parse(stream);
@@ -174,40 +201,51 @@ private uint ReadFrame<TPixel>(BufferedReadStream stream, ref Image<TPixel>? ima
                 break;
         }
 
-        ImageFrame<TPixel>? currentFrame = null;
-        ImageFrame<TPixel> imageFrame;
+        ImageFrame<TPixel> currentFrame;
         if (previousFrame is null)
         {
-            image = new Image<TPixel>(this.configuration, (int)width, (int)height, backgroundColor.ToPixel<TPixel>(), this.metadata);
-
-            SetFrameMetadata(image.Frames.RootFrame.Metadata, frameData);
+            image = new Image<TPixel>(this.configuration, (int)width, (int)height, backgroundColor, this.metadata);
 
-            imageFrame = image.Frames.RootFrame;
+            currentFrame = image.Frames.RootFrame;
+            SetFrameMetadata(currentFrame.Metadata, frameData);
         }
         else
         {
-            currentFrame = image!.Frames.AddFrame(previousFrame); // This clones the frame and adds it the collection.
+            // If the frame is a key frame we do not need to clone the frame or clear it.
+            bool isKeyFrame = prevFrameData?.DisposalMethod is FrameDisposalMode.RestoreToBackground
+                 && this.restoreArea == image!.Bounds;
 
-            SetFrameMetadata(currentFrame.Metadata, frameData);
+            if (isKeyFrame)
+            {
+                currentFrame = image!.Frames.CreateFrame(backgroundColor);
+            }
+            else
+            {
+                // This clones the frame and adds it the collection.
+                currentFrame = image!.Frames.AddFrame(previousFrame);
+                if (prevFrameData?.DisposalMethod is FrameDisposalMode.RestoreToBackground)
+                {
+                    this.RestoreToBackground(currentFrame, backgroundColor);
+                }
+            }
 
-            imageFrame = currentFrame;
+            SetFrameMetadata(currentFrame.Metadata, frameData);
         }
 
-        Rectangle regionRectangle = frameData.Bounds;
+        Rectangle interest = frameData.Bounds;
+        bool blend = previousFrame != null && frameData.BlendingMethod == FrameBlendMode.Over;
+        using Buffer2D<TPixel> pixelData = this.DecodeImageFrameData<TPixel>(frameData, webpInfo);
+        DrawDecodedImageFrameOnCanvas(pixelData, currentFrame, interest, blend);
+
+        webpInfo?.Dispose();
+        previousFrame = currentFrame;
+        prevFrameData = frameData;
 
         if (frameData.DisposalMethod is FrameDisposalMode.RestoreToBackground)
         {
-            this.RestoreToBackground(imageFrame, backgroundColor);
+            this.restoreArea = interest;
         }
 
-        using Buffer2D<TPixel> decodedImageFrame = this.DecodeImageFrameData<TPixel>(frameData, webpInfo);
-
-        bool blend = previousFrame != null && frameData.BlendingMethod == FrameBlendMode.Over;
-        DrawDecodedImageFrameOnCanvas(decodedImageFrame, imageFrame, regionRectangle, blend);
-
-        previousFrame = currentFrame ?? image.Frames.RootFrame;
-        this.restoreArea = regionRectangle;
-
         return (uint)(stream.Position - streamStartPosition);
     }
 
@@ -257,31 +295,26 @@ private Buffer2D<TPixel> DecodeImageFrameData<TPixel>(WebpFrameData frameData, W
 
         try
         {
-            Buffer2D<TPixel> pixelBufferDecoded = decodedFrame.PixelBuffer;
+            Buffer2D<TPixel> decodeBuffer = decodedFrame.PixelBuffer;
             if (webpInfo.IsLossless)
             {
-                WebpLosslessDecoder losslessDecoder =
-                    new(webpInfo.Vp8LBitReader, this.memoryAllocator, this.configuration);
-                losslessDecoder.Decode(pixelBufferDecoded, (int)webpInfo.Width, (int)webpInfo.Height);
+                WebpLosslessDecoder losslessDecoder = new(webpInfo.Vp8LBitReader, this.memoryAllocator, this.configuration);
+                losslessDecoder.Decode(decodeBuffer, (int)webpInfo.Width, (int)webpInfo.Height);
             }
             else
             {
                 WebpLossyDecoder lossyDecoder =
                     new(webpInfo.Vp8BitReader, this.memoryAllocator, this.configuration);
-                lossyDecoder.Decode(pixelBufferDecoded, (int)webpInfo.Width, (int)webpInfo.Height, webpInfo, this.alphaData);
+                lossyDecoder.Decode(decodeBuffer, (int)webpInfo.Width, (int)webpInfo.Height, webpInfo, this.alphaData);
             }
 
-            return pixelBufferDecoded;
+            return decodeBuffer;
         }
         catch
         {
             decodedFrame?.Dispose();
             throw;
         }
-        finally
-        {
-            webpInfo.Dispose();
-        }
     }
 
     /// <summary>
@@ -335,7 +368,7 @@ private static void DrawDecodedImageFrameOnCanvas<TPixel>(
     /// <typeparam name="TPixel">The pixel format.</typeparam>
     /// <param name="imageFrame">The image frame.</param>
     /// <param name="backgroundColor">Color of the background.</param>
-    private void RestoreToBackground<TPixel>(ImageFrame<TPixel> imageFrame, Color backgroundColor)
+    private void RestoreToBackground<TPixel>(ImageFrame<TPixel> imageFrame, TPixel backgroundColor)
         where TPixel : unmanaged, IPixel<TPixel>
     {
         if (!this.restoreArea.HasValue)
@@ -345,8 +378,9 @@ private void RestoreToBackground<TPixel>(ImageFrame<TPixel> imageFrame, Color ba
 
         Rectangle interest = Rectangle.Intersect(imageFrame.Bounds, this.restoreArea.Value);
         Buffer2DRegion<TPixel> pixelRegion = imageFrame.PixelBuffer.GetRegion(interest);
-        TPixel backgroundPixel = backgroundColor.ToPixel<TPixel>();
-        pixelRegion.Fill(backgroundPixel);
+        pixelRegion.Fill(backgroundColor);
+
+        this.restoreArea = null;
     }
 
     /// <inheritdoc/>
diff --git a/src/ImageSharp/Formats/Webp/WebpCommonUtils.cs b/src/ImageSharp/Formats/Webp/WebpCommonUtils.cs
index a1e9821c09..1ca409f9a4 100644
--- a/src/ImageSharp/Formats/Webp/WebpCommonUtils.cs
+++ b/src/ImageSharp/Formats/Webp/WebpCommonUtils.cs
@@ -18,7 +18,7 @@ internal static class WebpCommonUtils
     /// </summary>
     /// <param name="row">The row to check.</param>
     /// <returns>Returns true if alpha has non-0xff values.</returns>
-    public static unsafe bool CheckNonOpaque(Span<Bgra32> row)
+    public static unsafe bool CheckNonOpaque(ReadOnlySpan<Bgra32> row)
     {
         if (Avx2.IsSupported)
         {
diff --git a/src/ImageSharp/ImageSharp.csproj b/src/ImageSharp/ImageSharp.csproj
index 0d36340bf8..36c9375bd6 100644
--- a/src/ImageSharp/ImageSharp.csproj
+++ b/src/ImageSharp/ImageSharp.csproj
@@ -44,6 +44,11 @@
     <None Include="..\..\LICENSE" Pack="true" PackagePath="" />
     <None Include="..\..\shared-infrastructure\branding\icons\imagesharp\sixlabors.imagesharp.128.png" Pack="true" PackagePath="" />
     <None Include="..\..\SixLabors.ImageSharp.props" Pack="true" PackagePath="build" />
+    <None Include="Common\InlineArray.cs">
+      <DesignTime>True</DesignTime>
+      <AutoGen>True</AutoGen>
+      <DependentUpon>InlineArray.tt</DependentUpon>
+    </None>
   </ItemGroup>
 
   <ItemGroup>
@@ -51,6 +56,11 @@
   </ItemGroup>
 
   <ItemGroup>
+    <Compile Update="Common\InlineArray.cs">
+      <DesignTime>True</DesignTime>
+      <AutoGen>True</AutoGen>
+      <DependentUpon>InlineArray.tt</DependentUpon>
+    </Compile>
     <Compile Update="Formats\_Generated\ImageMetadataExtensions.cs">
       <DesignTime>True</DesignTime>
       <AutoGen>True</AutoGen>
@@ -154,6 +164,10 @@
   </ItemGroup>
 
   <ItemGroup>
+    <None Update="Common\InlineArray.tt">
+      <Generator>TextTemplatingFileGenerator</Generator>
+      <LastGenOutput>InlineArray.cs</LastGenOutput>
+    </None>
     <None Update="Formats\_Generated\ImageMetadataExtensions.tt">
       <LastGenOutput>ImageMetadataExtensions.cs</LastGenOutput>
       <Generator>TextTemplatingFileGenerator</Generator>
diff --git a/src/ImageSharp/IndexedImageFrame{TPixel}.cs b/src/ImageSharp/IndexedImageFrame{TPixel}.cs
index 6807e77ad2..49c9e33eb1 100644
--- a/src/ImageSharp/IndexedImageFrame{TPixel}.cs
+++ b/src/ImageSharp/IndexedImageFrame{TPixel}.cs
@@ -30,7 +30,7 @@ public sealed class IndexedImageFrame<TPixel> : IPixelSource, IDisposable
     /// <param name="width">The frame width.</param>
     /// <param name="height">The frame height.</param>
     /// <param name="palette">The color palette.</param>
-    internal IndexedImageFrame(Configuration configuration, int width, int height, ReadOnlyMemory<TPixel> palette)
+    public IndexedImageFrame(Configuration configuration, int width, int height, ReadOnlyMemory<TPixel> palette)
     {
         Guard.NotNull(configuration, nameof(configuration));
         Guard.MustBeLessThanOrEqualTo(palette.Length, QuantizerConstants.MaxColors, nameof(palette));
@@ -42,7 +42,7 @@ internal IndexedImageFrame(Configuration configuration, int width, int height, R
         this.Height = height;
         this.pixelBuffer = configuration.MemoryAllocator.Allocate2D<byte>(width, height);
 
-        // Copy the palette over. We want the lifetime of this frame to be independant of any palette source.
+        // Copy the palette over. We want the lifetime of this frame to be independent of any palette source.
         this.paletteOwner = configuration.MemoryAllocator.Allocate<TPixel>(palette.Length);
         palette.Span.CopyTo(this.paletteOwner.GetSpan());
         this.Palette = this.paletteOwner.Memory[..palette.Length];
diff --git a/src/ImageSharp/Processing/Processors/CloningImageProcessor{TPixel}.cs b/src/ImageSharp/Processing/Processors/CloningImageProcessor{TPixel}.cs
index abe32e3882..bc34f759a0 100644
--- a/src/ImageSharp/Processing/Processors/CloningImageProcessor{TPixel}.cs
+++ b/src/ImageSharp/Processing/Processors/CloningImageProcessor{TPixel}.cs
@@ -132,16 +132,14 @@ protected virtual void BeforeFrameApply(ImageFrame<TPixel> source, ImageFrame<TP
     /// <param name="source">The source image. Cannot be null.</param>
     /// <param name="destination">The cloned/destination image. Cannot be null.</param>
     protected virtual void AfterFrameApply(ImageFrame<TPixel> source, ImageFrame<TPixel> destination)
-    {
-    }
+        => destination.Metadata.AfterFrameApply(source, destination);
 
     /// <summary>
     /// This method is called after the process is applied to prepare the processor.
     /// </summary>
     /// <param name="destination">The cloned/destination image. Cannot be null.</param>
     protected virtual void AfterImageApply(Image<TPixel> destination)
-    {
-    }
+        => destination.Metadata.AfterImageApply(destination);
 
     /// <summary>
     /// Disposes the object and frees resources for the Garbage Collector.
diff --git a/src/ImageSharp/Processing/Processors/Dithering/IDither.cs b/src/ImageSharp/Processing/Processors/Dithering/IDither.cs
index ac2921b98d..3217601270 100644
--- a/src/ImageSharp/Processing/Processors/Dithering/IDither.cs
+++ b/src/ImageSharp/Processing/Processors/Dithering/IDither.cs
@@ -21,7 +21,7 @@ public interface IDither
     /// <param name="source">The source image.</param>
     /// <param name="destination">The destination quantized frame.</param>
     /// <param name="bounds">The region of interest bounds.</param>
-    void ApplyQuantizationDither<TFrameQuantizer, TPixel>(
+    public void ApplyQuantizationDither<TFrameQuantizer, TPixel>(
         ref TFrameQuantizer quantizer,
         ImageFrame<TPixel> source,
         IndexedImageFrame<TPixel> destination,
@@ -38,7 +38,7 @@ void ApplyQuantizationDither<TFrameQuantizer, TPixel>(
     /// <param name="processor">The palette dithering processor.</param>
     /// <param name="source">The source image.</param>
     /// <param name="bounds">The region of interest bounds.</param>
-    void ApplyPaletteDither<TPaletteDitherImageProcessor, TPixel>(
+    public void ApplyPaletteDither<TPaletteDitherImageProcessor, TPixel>(
         in TPaletteDitherImageProcessor processor,
         ImageFrame<TPixel> source,
         Rectangle bounds)
diff --git a/src/ImageSharp/Processing/Processors/Dithering/IPaletteDitherImageProcessor{TPixel}.cs b/src/ImageSharp/Processing/Processors/Dithering/IPaletteDitherImageProcessor{TPixel}.cs
index e406d82c69..347e2f0ef6 100644
--- a/src/ImageSharp/Processing/Processors/Dithering/IPaletteDitherImageProcessor{TPixel}.cs
+++ b/src/ImageSharp/Processing/Processors/Dithering/IPaletteDitherImageProcessor{TPixel}.cs
@@ -15,22 +15,22 @@ public interface IPaletteDitherImageProcessor<TPixel>
     /// <summary>
     /// Gets the configuration instance to use when performing operations.
     /// </summary>
-    Configuration Configuration { get; }
+    public Configuration Configuration { get; }
 
     /// <summary>
     /// Gets the dithering palette.
     /// </summary>
-    ReadOnlyMemory<TPixel> Palette { get; }
+    public ReadOnlyMemory<TPixel> Palette { get; }
 
     /// <summary>
     /// Gets the dithering scale used to adjust the amount of dither. Range 0..1.
     /// </summary>
-    float DitherScale { get; }
+    public float DitherScale { get; }
 
     /// <summary>
     /// Returns the color from the dithering palette corresponding to the given color.
     /// </summary>
     /// <param name="color">The color to match.</param>
     /// <returns>The <typeparamref name="TPixel"/> match.</returns>
-    TPixel GetPaletteColor(TPixel color);
+    public TPixel GetPaletteColor(TPixel color);
 }
diff --git a/src/ImageSharp/Processing/Processors/ImageProcessor{TPixel}.cs b/src/ImageSharp/Processing/Processors/ImageProcessor{TPixel}.cs
index 2fa79220e5..e1f7d1fffb 100644
--- a/src/ImageSharp/Processing/Processors/ImageProcessor{TPixel}.cs
+++ b/src/ImageSharp/Processing/Processors/ImageProcessor{TPixel}.cs
@@ -95,7 +95,7 @@ protected virtual void BeforeFrameApply(ImageFrame<TPixel> source)
     protected abstract void OnFrameApply(ImageFrame<TPixel> source);
 
     /// <summary>
-    /// This method is called after the process is applied to prepare the processor.
+    /// This method is called after the process is applied to each frame.
     /// </summary>
     /// <param name="source">The source image. Cannot be null.</param>
     protected virtual void AfterFrameApply(ImageFrame<TPixel> source)
@@ -103,11 +103,10 @@ protected virtual void AfterFrameApply(ImageFrame<TPixel> source)
     }
 
     /// <summary>
-    /// This method is called after the process is applied to prepare the processor.
+    /// This method is called after the process is applied to the complete image.
     /// </summary>
     protected virtual void AfterImageApply()
-    {
-    }
+        => this.Source.Metadata.AfterImageApply(this.Source);
 
     /// <summary>
     /// Disposes the object and frees resources for the Garbage Collector.
diff --git a/src/ImageSharp/Processing/Processors/Quantization/EuclideanPixelMap{TPixel}.cs b/src/ImageSharp/Processing/Processors/Quantization/EuclideanPixelMap{TPixel}.cs
index 4fd37d479d..d11376e3ba 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/EuclideanPixelMap{TPixel}.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/EuclideanPixelMap{TPixel}.cs
@@ -2,6 +2,7 @@
 // Licensed under the Six Labors Split License.
 
 using System.Buffers;
+using System.Numerics;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 using SixLabors.ImageSharp.Memory;
@@ -21,13 +22,7 @@ internal sealed class EuclideanPixelMap<TPixel> : IDisposable
     where TPixel : unmanaged, IPixel<TPixel>
 {
     private Rgba32[] rgbaPalette;
-    private int transparentIndex;
-    private readonly TPixel transparentMatch;
-
-    /// <summary>
-    /// Do not make this readonly! Struct value would be always copied on non-readonly method calls.
-    /// </summary>
-    private ColorDistanceCache cache;
+    private readonly HybridColorDistanceCache cache;
     private readonly Configuration configuration;
 
     /// <summary>
@@ -36,26 +31,12 @@ internal sealed class EuclideanPixelMap<TPixel> : IDisposable
     /// <param name="configuration">The configuration.</param>
     /// <param name="palette">The color palette to map from.</param>
     public EuclideanPixelMap(Configuration configuration, ReadOnlyMemory<TPixel> palette)
-        : this(configuration, palette, -1)
-    {
-    }
-
-    /// <summary>
-    /// Initializes a new instance of the <see cref="EuclideanPixelMap{TPixel}"/> class.
-    /// </summary>
-    /// <param name="configuration">The configuration.</param>
-    /// <param name="palette">The color palette to map from.</param>
-    /// <param name="transparentIndex">An explicit index at which to match transparent pixels.</param>
-    public EuclideanPixelMap(Configuration configuration, ReadOnlyMemory<TPixel> palette, int transparentIndex = -1)
     {
         this.configuration = configuration;
         this.Palette = palette;
         this.rgbaPalette = new Rgba32[palette.Length];
-        this.cache = new ColorDistanceCache(configuration.MemoryAllocator);
+        this.cache = new HybridColorDistanceCache(configuration.MemoryAllocator);
         PixelOperations<TPixel>.Instance.ToRgba32(configuration, this.Palette.Span, this.rgbaPalette);
-
-        this.transparentIndex = transparentIndex;
-        this.transparentMatch = TPixel.FromRgba32(default);
     }
 
     /// <summary>
@@ -70,21 +51,27 @@ public EuclideanPixelMap(Configuration configuration, ReadOnlyMemory<TPixel> pal
     /// </summary>
     /// <param name="color">The color to match.</param>
     /// <param name="match">The matched color.</param>
+    /// <param name="transparencyThreshold">The transparency threshold.</param>
     /// <returns>The <see cref="int"/> index.</returns>
-    [MethodImpl(InliningOptions.ShortMethod)]
-    public int GetClosestColor(TPixel color, out TPixel match)
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public int GetClosestColor(TPixel color, out TPixel match, short transparencyThreshold = -1)
     {
         ref TPixel paletteRef = ref MemoryMarshal.GetReference(this.Palette.Span);
         Rgba32 rgba = color.ToRgba32();
 
+        if (transparencyThreshold > -1 && rgba.A < transparencyThreshold)
+        {
+            rgba = default;
+        }
+
         // Check if the color is in the lookup table
-        if (!this.cache.TryGetValue(rgba, out short index))
+        if (this.cache.TryGetValue(rgba, out short index))
         {
-            return this.GetClosestColorSlow(rgba, ref paletteRef, out match);
+            match = Unsafe.Add(ref paletteRef, (ushort)index);
+            return index;
         }
 
-        match = Unsafe.Add(ref paletteRef, (ushort)index);
-        return index;
+        return this.GetClosestColorSlow(rgba, ref paletteRef, out match);
     }
 
     /// <summary>
@@ -96,46 +83,25 @@ public void Clear(ReadOnlyMemory<TPixel> palette)
         this.Palette = palette;
         this.rgbaPalette = new Rgba32[palette.Length];
         PixelOperations<TPixel>.Instance.ToRgba32(this.configuration, this.Palette.Span, this.rgbaPalette);
-        this.transparentIndex = -1;
         this.cache.Clear();
     }
 
-    /// <summary>
-    /// Allows setting the transparent index after construction.
-    /// </summary>
-    /// <param name="index">An explicit index at which to match transparent pixels.</param>
-    public void SetTransparentIndex(int index)
-    {
-        if (index != this.transparentIndex)
-        {
-            this.cache.Clear();
-        }
-
-        this.transparentIndex = index;
-    }
-
-    [MethodImpl(InliningOptions.ShortMethod)]
+    [MethodImpl(MethodImplOptions.NoInlining)]
     private int GetClosestColorSlow(Rgba32 rgba, ref TPixel paletteRef, out TPixel match)
     {
         // Loop through the palette and find the nearest match.
         int index = 0;
-
-        if (this.transparentIndex >= 0 && rgba == default)
-        {
-            // We have explicit instructions. No need to search.
-            index = this.transparentIndex;
-            this.cache.Add(rgba, (byte)index);
-            match = this.transparentMatch;
-            return index;
-        }
-
         float leastDistance = float.MaxValue;
         for (int i = 0; i < this.rgbaPalette.Length; i++)
         {
             Rgba32 candidate = this.rgbaPalette[i];
-            float distance = DistanceSquared(rgba, candidate);
+            if (candidate.PackedValue == rgba.PackedValue)
+            {
+                index = i;
+                break;
+            }
 
-            // If it's an exact match, exit the loop
+            float distance = DistanceSquared(rgba, candidate);
             if (distance == 0)
             {
                 index = i;
@@ -144,7 +110,6 @@ private int GetClosestColorSlow(Rgba32 rgba, ref TPixel paletteRef, out TPixel m
 
             if (distance < leastDistance)
             {
-                // Less than... assign.
                 index = i;
                 leastDistance = distance;
             }
@@ -153,6 +118,7 @@ private int GetClosestColorSlow(Rgba32 rgba, ref TPixel paletteRef, out TPixel m
         // Now I have the index, pop it into the cache for next time
         this.cache.Add(rgba, (byte)index);
         match = Unsafe.Add(ref paletteRef, (uint)index);
+
         return index;
     }
 
@@ -162,96 +128,415 @@ private int GetClosestColorSlow(Rgba32 rgba, ref TPixel paletteRef, out TPixel m
     /// <param name="a">The first point.</param>
     /// <param name="b">The second point.</param>
     /// <returns>The distance squared.</returns>
-    [MethodImpl(InliningOptions.ShortMethod)]
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
     private static float DistanceSquared(Rgba32 a, Rgba32 b)
     {
-        float deltaR = a.R - b.R;
-        float deltaG = a.G - b.G;
-        float deltaB = a.B - b.B;
-        float deltaA = a.A - b.A;
-        return (deltaR * deltaR) + (deltaG * deltaG) + (deltaB * deltaB) + (deltaA * deltaA);
+        Vector4 va = new(a.R, a.G, a.B, a.A);
+        Vector4 vb = new(b.R, b.G, b.B, b.A);
+        return Vector4.DistanceSquared(va, vb);
     }
 
     public void Dispose() => this.cache.Dispose();
 
     /// <summary>
-    /// A cache for storing color distance matching results.
+    /// A hybrid color distance cache that combines a small, fixed-capacity exact-match dictionary
+    /// (ExactCache, ~4–5 KB for up to 512 entries) with a coarse lookup table (CoarseCache) for 5,5,5,6 precision.
     /// </summary>
     /// <remarks>
-    /// <para>
-    /// The granularity of the cache has been determined based upon the current
-    /// suite of test images and provides the lowest possible memory usage while
-    /// providing enough match accuracy.
-    /// Entry count is currently limited to 2335905 entries (4MB).
-    /// </para>
+    /// ExactCache provides O(1) lookup for common cases using a simple 256-entry hash-based dictionary, while CoarseCache
+    /// quantizes RGB channels to 5 bits (yielding 32^3 buckets) and alpha to 6 bits, storing up to 4 alpha entries per bucket
+    /// (a design chosen based on probability theory to capture most real-world variations) for a total memory footprint of
+    /// roughly 576 KB. Lookups and insertions are performed in constant time, making the overall design both fast and memory-predictable.
     /// </remarks>
-    private unsafe struct ColorDistanceCache : IDisposable
+#pragma warning disable CA1001 // Types that own disposable fields should be disposable
+    // https://github.com/dotnet/roslyn-analyzers/issues/6151
+    private readonly unsafe struct HybridColorDistanceCache : IDisposable
+#pragma warning restore CA1001 // Types that own disposable fields should be disposable
     {
-        private const int IndexRBits = 5;
-        private const int IndexGBits = 5;
-        private const int IndexBBits = 5;
-        private const int IndexABits = 6;
-        private const int IndexRCount = (1 << IndexRBits) + 1;
-        private const int IndexGCount = (1 << IndexGBits) + 1;
-        private const int IndexBCount = (1 << IndexBBits) + 1;
-        private const int IndexACount = (1 << IndexABits) + 1;
-        private const int RShift = 8 - IndexRBits;
-        private const int GShift = 8 - IndexGBits;
-        private const int BShift = 8 - IndexBBits;
-        private const int AShift = 8 - IndexABits;
-        private const int Entries = IndexRCount * IndexGCount * IndexBCount * IndexACount;
-        private MemoryHandle tableHandle;
-        private readonly IMemoryOwner<short> table;
-        private readonly short* tablePointer;
-
-        public ColorDistanceCache(MemoryAllocator allocator)
+        private readonly CoarseCache coarseCache;
+        private readonly ExactCache exactCache;
+
+        public HybridColorDistanceCache(MemoryAllocator allocator)
+        {
+            this.exactCache = new ExactCache(allocator);
+            this.coarseCache = new CoarseCache(allocator);
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public readonly void Add(Rgba32 color, short index)
         {
-            this.table = allocator.Allocate<short>(Entries);
-            this.table.GetSpan().Fill(-1);
-            this.tableHandle = this.table.Memory.Pin();
-            this.tablePointer = (short*)this.tableHandle.Pointer;
+            if (this.exactCache.TryAdd(color.PackedValue, index))
+            {
+                return;
+            }
+
+            this.coarseCache.Add(color, index);
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public readonly bool TryGetValue(Rgba32 color, out short match)
+        {
+            if (this.exactCache.TryGetValue(color.PackedValue, out match))
+            {
+                return true; // Exact match found
+            }
+
+            if (this.coarseCache.TryGetValue(color, out match))
+            {
+                return true; // Coarse match found
+            }
+
+            match = -1;
+            return false;
+        }
+
+        public readonly void Clear()
+        {
+            this.exactCache.Clear();
+            this.coarseCache.Clear();
+        }
+
+        public void Dispose()
+        {
+            this.exactCache.Dispose();
+            this.coarseCache.Dispose();
+        }
+    }
+
+    /// <summary>
+    /// A fixed-capacity dictionary with exactly 512 entries mapping a <see cref="uint"/> key
+    /// to a <see cref="short"/> value.
+    /// </summary>
+    /// <remarks>
+    /// The dictionary is implemented using a fixed array of 512 buckets and an entries array
+    /// of the same size. The bucket for a key is computed as (key &amp; 0x1FF), and collisions are
+    /// resolved through a linked chain stored in the <see cref="Entry.Next"/> field.
+    /// The overall memory usage is approximately 4–5 KB. Both lookup and insertion operations are,
+    /// on average, O(1) since the bucket is determined via a simple bitmask and collision chains are
+    /// typically very short; in the worst-case, the number of iterations is bounded by 256.
+    /// This guarantees highly efficient and predictable performance for small, fixed-size color palettes.
+    /// </remarks>
+    internal sealed unsafe class ExactCache : IDisposable
+    {
+        // Buckets array: each bucket holds the index (0-based) into the entries array
+        // of the first entry in the chain, or -1 if empty.
+        private readonly IMemoryOwner<short> bucketsOwner;
+        private MemoryHandle bucketsHandle;
+        private short* buckets;
+
+        // Entries array: stores up to 256 entries.
+        private readonly IMemoryOwner<Entry> entriesOwner;
+        private MemoryHandle entriesHandle;
+        private Entry* entries;
+
+        public const int Capacity = 512;
+
+        public ExactCache(MemoryAllocator allocator)
+        {
+            this.Count = 0;
+
+            // Allocate exactly 512 ints for buckets.
+            this.bucketsOwner = allocator.Allocate<short>(Capacity, AllocationOptions.Clean);
+            Span<short> bucketSpan = this.bucketsOwner.GetSpan();
+            bucketSpan.Fill(-1);
+            this.bucketsHandle = this.bucketsOwner.Memory.Pin();
+            this.buckets = (short*)this.bucketsHandle.Pointer;
+
+            // Allocate exactly 512 entries.
+            this.entriesOwner = allocator.Allocate<Entry>(Capacity, AllocationOptions.Clean);
+            this.entriesHandle = this.entriesOwner.Memory.Pin();
+            this.entries = (Entry*)this.entriesHandle.Pointer;
         }
 
-        [MethodImpl(InliningOptions.ShortMethod)]
-        public readonly void Add(Rgba32 rgba, byte index)
+        public int Count { get; private set; }
+
+        /// <summary>
+        /// Adds a key/value pair to the dictionary.
+        /// If the key already exists, the dictionary is left unchanged.
+        /// </summary>
+        /// <param name="key">The key to add.</param>
+        /// <param name="value">The value to add.</param>
+        /// <returns><see langword="true"/> if the key was added; otherwise, <see langword="false"/>.</returns>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public bool TryAdd(uint key, short value)
         {
-            int idx = GetPaletteIndex(rgba);
-            this.tablePointer[idx] = index;
+            if (this.Count == Capacity)
+            {
+                return false; // Dictionary is full.
+            }
+
+            // The key is a 32-bit unsigned integer representing an RGBA color, where the bytes are laid out as R|G|B|A
+            // (with R in the most significant byte and A in the least significant).
+            // To compute the bucket index:
+            // 1. (key >> 16) extracts the top 16 bits, effectively giving us the R and G channels.
+            // 2. (key >> 8) shifts the key right by 8 bits, bringing R, G, and B into the lower 24 bits (dropping A).
+            // 3. XORing these two values with the original key mixes bits from all four channels (R, G, B, and A),
+            //    which helps to counteract situations where one or more channels have a limited range.
+            // 4. Finally, we apply a bitmask of 0x1FF to keep only the lowest 9 bits, ensuring the result is between 0 and 511,
+            //    which corresponds to our fixed bucket count of 512.
+            int bucket = (int)(((key >> 16) ^ (key >> 8) ^ key) & 0x1FF);
+            int i = this.buckets[bucket];
+
+            // Traverse the collision chain.
+            Entry* entries = this.entries;
+            while (i != -1)
+            {
+                Entry e = entries[i];
+                if (e.Key == key)
+                {
+                    // Key already exists; do not overwrite.
+                    return false;
+                }
+
+                i = e.Next;
+            }
+
+            short index = (short)this.Count;
+            this.Count++;
+
+            // Insert the new entry:
+            entries[index].Key = key;
+            entries[index].Value = value;
+
+            // Link this new entry into the bucket chain.
+            entries[index].Next = this.buckets[bucket];
+            this.buckets[bucket] = index;
+            return true;
         }
 
-        [MethodImpl(InliningOptions.ShortMethod)]
-        public readonly bool TryGetValue(Rgba32 rgba, out short match)
+        /// <summary>
+        /// Tries to retrieve the value associated with the specified key.
+        /// Returns true if the key is found; otherwise, returns false.
+        /// </summary>
+        /// <param name="key">The key to search for.</param>
+        /// <param name="value">The value associated with the key, if found.</param>
+        /// <returns><see langword="true"/> if the key is found; otherwise, <see langword="false"/>.</returns>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public bool TryGetValue(uint key, out short value)
         {
-            int idx = GetPaletteIndex(rgba);
-            match = this.tablePointer[idx];
-            return match > -1;
+            int bucket = (int)(((key >> 16) ^ (key >> 8) ^ key) & 0x1FF);
+            int i = this.buckets[bucket];
+
+            // If the bucket is empty, return immediately.
+            if (i == -1)
+            {
+                value = -1;
+                return false;
+            }
+
+            // Traverse the chain.
+            Entry* entries = this.entries;
+            do
+            {
+                Entry e = entries[i];
+                if (e.Key == key)
+                {
+                    value = e.Value;
+                    return true;
+                }
+
+                i = e.Next;
+            }
+            while (i != -1);
+
+            value = -1;
+            return false;
         }
 
         /// <summary>
-        /// Clears the cache resetting each entry to empty.
+        /// Clears the dictionary.
         /// </summary>
-        [MethodImpl(InliningOptions.ShortMethod)]
-        public readonly void Clear() => this.table.GetSpan().Fill(-1);
+        public void Clear()
+        {
+            Span<short> bucketSpan = this.bucketsOwner.GetSpan();
+            bucketSpan.Fill(-1);
+            this.Count = 0;
+        }
 
-        [MethodImpl(InliningOptions.ShortMethod)]
-        private static int GetPaletteIndex(Rgba32 rgba)
+        public void Dispose()
         {
-            int rIndex = rgba.R >> RShift;
-            int gIndex = rgba.G >> GShift;
-            int bIndex = rgba.B >> BShift;
-            int aIndex = rgba.A >> AShift;
-
-            return (aIndex * (IndexRCount * IndexGCount * IndexBCount)) +
-                   (rIndex * (IndexGCount * IndexBCount)) +
-                   (gIndex * IndexBCount) + bIndex;
+            this.bucketsHandle.Dispose();
+            this.bucketsOwner.Dispose();
+            this.entriesHandle.Dispose();
+            this.entriesOwner.Dispose();
+            this.buckets = null;
+            this.entries = null;
+        }
+
+        private struct Entry
+        {
+            public uint Key;     // The key (packed RGBA)
+            public short Value;  // The value; -1 means unused.
+            public short Next;     // Index of the next entry in the chain, or -1 if none.
+        }
+    }
+
+    /// <summary>
+    /// <para>
+    /// CoarseCache is a fast, low-memory lookup structure for caching palette indices associated with RGBA values,
+    /// using a quantized representation of 5,5,5,6 (RGB: 5 bits each, Alpha: 6 bits).
+    /// </para>
+    /// <para>
+    /// The cache quantizes the RGB channels to 5 bits each, resulting in 32 levels per channel and a total of 32³ = 32,768 buckets.
+    /// Each bucket is represented by an <see cref="AlphaBucket"/>, which holds a small, inline array of alpha entries.
+    /// Each alpha entry stores the alpha value quantized to 6 bits (0–63) along with a palette index (a 16-bit value).
+    /// </para>
+    /// <para>
+    /// Performance Characteristics:
+    ///   - Lookup: O(1) for computing the bucket index from the RGB channels, plus a small constant time (up to 4 iterations)
+    ///     to search through the alpha entries in the bucket.
+    ///   - Insertion: O(1) for bucket index computation and a quick linear search over a very small (fixed) number of entries.
+    /// </para>
+    /// <para>
+    /// Memory Characteristics:
+    ///   - The cache consists of 32,768 buckets.
+    ///   - Each <see cref="AlphaBucket"/> is implemented using an inline array with a capacity of 4 entries.
+    ///   - Each bucket occupies approximately 18 bytes.
+    ///   - Overall, the buckets occupy roughly 32,768 × 18 = 589,824 bytes (576 KB).
+    /// </para>
+    /// <para>
+    /// This design provides nearly constant-time lookup and insertion with minimal memory usage,
+    /// making it ideal for applications such as color distance caching in images with a limited palette (up to 256 entries).
+    /// </para>
+    /// </summary>
+    internal sealed unsafe class CoarseCache : IDisposable
+    {
+        // Use 5 bits per channel for R, G, and B: 32 levels each.
+        // Total buckets = 32^3 = 32768.
+        private const int RgbBits = 5;
+        private const int BucketCount = 1 << (RgbBits * 3); // 32768
+        private readonly IMemoryOwner<AlphaBucket> bucketsOwner;
+        private readonly AlphaBucket* buckets;
+        private MemoryHandle bucketHandle;
+
+        public CoarseCache(MemoryAllocator allocator)
+        {
+            this.bucketsOwner = allocator.Allocate<AlphaBucket>(BucketCount, AllocationOptions.Clean);
+            this.bucketHandle = this.bucketsOwner.Memory.Pin();
+            this.buckets = (AlphaBucket*)this.bucketHandle.Pointer;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static int GetBucketIndex(byte r, byte g, byte b)
+        {
+            int qr = r >> (8 - RgbBits);
+            int qg = g >> (8 - RgbBits);
+            int qb = b >> (8 - RgbBits);
+
+            // Combine the quantized channels into a single index.
+            return (qr << (RgbBits * 2)) | (qg << RgbBits) | qb;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static byte QuantizeAlpha(byte a)
+
+            // Quantize to 6 bits: shift right by (8 - 6) = 2 bits.
+            => (byte)(a >> 2);
+
+        public void Add(Rgba32 color, short paletteIndex)
+        {
+            int bucketIndex = GetBucketIndex(color.R, color.G, color.B);
+            byte quantAlpha = QuantizeAlpha(color.A);
+            this.buckets[bucketIndex].Add(quantAlpha, paletteIndex);
         }
 
         public void Dispose()
         {
-            if (this.table != null)
+            this.bucketHandle.Dispose();
+            this.bucketsOwner.Dispose();
+        }
+
+        public bool TryGetValue(Rgba32 color, out short paletteIndex)
+        {
+            int bucketIndex = GetBucketIndex(color.R, color.G, color.B);
+            byte quantAlpha = QuantizeAlpha(color.A);
+            return this.buckets[bucketIndex].TryGetValue(quantAlpha, out paletteIndex);
+        }
+
+        public void Clear()
+        {
+            Span<AlphaBucket> bucketsSpan = this.bucketsOwner.GetSpan();
+            bucketsSpan.Clear();
+        }
+
+        public struct AlphaEntry
+        {
+            // Store the alpha value quantized to 6 bits (0..63)
+            public byte QuantizedAlpha;
+            public short PaletteIndex;
+        }
+
+        public struct AlphaBucket
+        {
+            // Fixed capacity for alpha entries in this bucket.
+            // We choose a capacity of 4 for several reasons:
+            //
+            // 1. The alpha channel is quantized to 6 bits, so there are 64 possible distinct values.
+            //    In the worst-case, a given RGB bucket might encounter up to 64 different alpha values.
+            //
+            // 2. However, in practice (based on probability theory and typical image data),
+            //    the number of unique alpha values that actually occur for a given quantized RGB
+            //    bucket is usually very small. If you randomly sample 4 values out of 64,
+            //    the probability that these 4 samples are all unique is high if the distribution
+            //    of alpha values is skewed or if only a few alpha values are used.
+            //
+            // 3. Statistically, for many real-world images, most RGB buckets will have only a couple
+            //    of unique alpha values. Allocating 4 slots per bucket provides a good trade-off:
+            //    it captures the common-case scenario while keeping overall memory usage low.
+            //
+            // 4. Even if more than 4 unique alpha values occur in a bucket,
+            //    our design overwrites the first entry. This behavior gives us some "wriggle room"
+            //    while preserving the most frequently encountered or most recent values.
+            public const int Capacity = 4;
+            public byte Count;
+            private InlineArray4<AlphaEntry> entries;
+
+            [MethodImpl(MethodImplOptions.AggressiveInlining)]
+            public bool TryGetValue(byte quantizedAlpha, out short paletteIndex)
             {
-                this.tableHandle.Dispose();
-                this.table.Dispose();
+                for (int i = 0; i < this.Count; i++)
+                {
+                    ref AlphaEntry entry = ref this.entries[i];
+                    if (entry.QuantizedAlpha == quantizedAlpha)
+                    {
+                        paletteIndex = entry.PaletteIndex;
+                        return true;
+                    }
+                }
+
+                paletteIndex = -1;
+                return false;
+            }
+
+            [MethodImpl(MethodImplOptions.AggressiveInlining)]
+            public void Add(byte quantizedAlpha, short paletteIndex)
+            {
+                // Check for an existing entry with the same quantized alpha.
+                for (int i = 0; i < this.Count; i++)
+                {
+                    ref AlphaEntry entry = ref this.entries[i];
+                    if (entry.QuantizedAlpha == quantizedAlpha)
+                    {
+                        // Update palette index if found.
+                        entry.PaletteIndex = paletteIndex;
+                        return;
+                    }
+                }
+
+                // If there's room, add a new entry.
+                if (this.Count < Capacity)
+                {
+                    ref AlphaEntry newEntry = ref this.entries[this.Count];
+                    newEntry.QuantizedAlpha = quantizedAlpha;
+                    newEntry.PaletteIndex = paletteIndex;
+                    this.Count++;
+                }
+                else
+                {
+                    // Bucket is full. Overwrite the first entry to give us some wriggle room.
+                    this.entries[0].QuantizedAlpha = quantizedAlpha;
+                    this.entries[0].PaletteIndex = paletteIndex;
+                }
             }
         }
     }
diff --git a/src/ImageSharp/Processing/Processors/Quantization/IQuantizer{TPixel}.cs b/src/ImageSharp/Processing/Processors/Quantization/IQuantizer{TPixel}.cs
index 35bbb1289e..dc5bdbd627 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/IQuantizer{TPixel}.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/IQuantizer{TPixel}.cs
@@ -16,12 +16,12 @@ public interface IQuantizer<TPixel> : IDisposable
     /// <summary>
     /// Gets the configuration.
     /// </summary>
-    Configuration Configuration { get; }
+    public Configuration Configuration { get; }
 
     /// <summary>
     /// Gets the quantizer options defining quantization rules.
     /// </summary>
-    QuantizerOptions Options { get; }
+    public QuantizerOptions Options { get; }
 
     /// <summary>
     /// Gets the quantized color palette.
@@ -29,13 +29,13 @@ public interface IQuantizer<TPixel> : IDisposable
     /// <exception cref="InvalidOperationException">
     /// The palette has not been built via <see cref="AddPaletteColors"/>.
     /// </exception>
-    ReadOnlyMemory<TPixel> Palette { get; }
+    public ReadOnlyMemory<TPixel> Palette { get; }
 
     /// <summary>
     /// Adds colors to the quantized palette from the given pixel source.
     /// </summary>
     /// <param name="pixelRegion">The <see cref="Buffer2DRegion{T}"/> of source pixels to register.</param>
-    void AddPaletteColors(Buffer2DRegion<TPixel> pixelRegion);
+    public void AddPaletteColors(in Buffer2DRegion<TPixel> pixelRegion);
 
     /// <summary>
     /// Quantizes an image frame and return the resulting output pixels.
@@ -49,7 +49,7 @@ public interface IQuantizer<TPixel> : IDisposable
     /// Only executes the second (quantization) step. The palette has to be built by calling <see cref="AddPaletteColors"/>.
     /// To run both steps, use <see cref="QuantizerUtilities.BuildPaletteAndQuantizeFrame{TPixel}"/>.
     /// </remarks>
-    IndexedImageFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> source, Rectangle bounds);
+    public IndexedImageFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> source, Rectangle bounds);
 
     /// <summary>
     /// Returns the index and color from the quantized palette corresponding to the given color.
@@ -57,7 +57,7 @@ public interface IQuantizer<TPixel> : IDisposable
     /// <param name="color">The color to match.</param>
     /// <param name="match">The matched color.</param>
     /// <returns>The <see cref="byte"/> index.</returns>
-    byte GetQuantizedColor(TPixel color, out TPixel match);
+    public byte GetQuantizedColor(TPixel color, out TPixel match);
 
     // TODO: Enable bulk operations.
     // void GetQuantizedColors(ReadOnlySpan<TPixel> colors, ReadOnlySpan<TPixel> palette, Span<byte> indices, Span<TPixel> matches);
diff --git a/src/ImageSharp/Processing/Processors/Quantization/OctreeQuantizer{TPixel}.cs b/src/ImageSharp/Processing/Processors/Quantization/OctreeQuantizer{TPixel}.cs
index 8b39b74579..be00bc433a 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/OctreeQuantizer{TPixel}.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/OctreeQuantizer{TPixel}.cs
@@ -30,6 +30,7 @@ public struct OctreeQuantizer<TPixel> : IQuantizer<TPixel>
     private ReadOnlyMemory<TPixel> palette;
     private EuclideanPixelMap<TPixel>? pixelMap;
     private readonly bool isDithering;
+    private readonly short transparencyThreshold;
     private bool isDisposed;
 
     /// <summary>
@@ -44,8 +45,9 @@ public OctreeQuantizer(Configuration configuration, QuantizerOptions options)
         this.Options = options;
 
         this.maxColors = this.Options.MaxColors;
+        this.transparencyThreshold = (short)(this.Options.TransparencyThreshold * 255);
         this.bitDepth = Numerics.Clamp(ColorNumerics.GetBitsNeededForColorDepth(this.maxColors), 1, 8);
-        this.octree = new Octree(this.bitDepth);
+        this.octree = new Octree(this.bitDepth, this.maxColors, this.transparencyThreshold, configuration.MemoryAllocator);
         this.paletteOwner = configuration.MemoryAllocator.Allocate<TPixel>(this.maxColors, AllocationOptions.Clean);
         this.pixelMap = default;
         this.palette = default;
@@ -60,65 +62,54 @@ public OctreeQuantizer(Configuration configuration, QuantizerOptions options)
     public QuantizerOptions Options { get; }
 
     /// <inheritdoc/>
-    public readonly ReadOnlyMemory<TPixel> Palette
+    public ReadOnlyMemory<TPixel> Palette
     {
         get
         {
-            QuantizerUtilities.CheckPaletteState(in this.palette);
+            if (this.palette.IsEmpty)
+            {
+                this.ResolvePalette();
+                QuantizerUtilities.CheckPaletteState(in this.palette);
+            }
+
             return this.palette;
         }
     }
 
     /// <inheritdoc/>
-    public void AddPaletteColors(Buffer2DRegion<TPixel> pixelRegion)
+    public readonly void AddPaletteColors(in Buffer2DRegion<TPixel> pixelRegion)
     {
-        using (IMemoryOwner<Rgba32> buffer = this.Configuration.MemoryAllocator.Allocate<Rgba32>(pixelRegion.Width))
+        using IMemoryOwner<Rgba32> buffer = this.Configuration.MemoryAllocator.Allocate<Rgba32>(pixelRegion.Width);
+        Span<Rgba32> bufferSpan = buffer.GetSpan();
+
+        // Loop through each row
+        for (int y = 0; y < pixelRegion.Height; y++)
         {
-            Span<Rgba32> bufferSpan = buffer.GetSpan();
+            Span<TPixel> row = pixelRegion.DangerousGetRowSpan(y);
+            PixelOperations<TPixel>.Instance.ToRgba32(this.Configuration, row, bufferSpan);
 
-            // Loop through each row
-            for (int y = 0; y < pixelRegion.Height; y++)
+            Octree octree = this.octree;
+            int transparencyThreshold = this.transparencyThreshold;
+            for (int x = 0; x < bufferSpan.Length; x++)
             {
-                Span<TPixel> row = pixelRegion.DangerousGetRowSpan(y);
-                PixelOperations<TPixel>.Instance.ToRgba32(this.Configuration, row, bufferSpan);
-
-                for (int x = 0; x < bufferSpan.Length; x++)
-                {
-                    Rgba32 rgba = bufferSpan[x];
-
-                    // Add the color to the Octree
-                    this.octree.AddColor(rgba);
-                }
+                // Add the color to the Octree
+                octree.AddColor(bufferSpan[x]);
             }
         }
+    }
 
-        int paletteIndex = 0;
+    private void ResolvePalette()
+    {
+        short paletteIndex = 0;
         Span<TPixel> paletteSpan = this.paletteOwner.GetSpan();
 
-        // On very rare occasions, (blur.png), the quantizer does not preserve a
-        // transparent entry when palletizing the captured colors.
-        // To workaround this we ensure the palette ends with the default color
-        // for higher bit depths. Lower bit depths will correctly reduce the palette.
-        // TODO: Investigate more evenly reduced palette reduction.
-        int max = this.maxColors;
-        if (this.bitDepth >= 4)
-        {
-            max--;
-        }
-
-        this.octree.Palletize(paletteSpan, max, ref paletteIndex);
+        this.octree.Palettize(paletteSpan, ref paletteIndex);
         ReadOnlyMemory<TPixel> result = this.paletteOwner.Memory[..paletteSpan.Length];
 
-        // When called multiple times by QuantizerUtilities.BuildPalette
-        // this prevents memory churn caused by reallocation.
-        if (this.pixelMap is null)
+        if (this.isDithering)
         {
             this.pixelMap = new EuclideanPixelMap<TPixel>(this.Configuration, result);
         }
-        else
-        {
-            this.pixelMap.Clear(result);
-        }
 
         this.palette = result;
     }
@@ -132,18 +123,19 @@ public readonly IndexedImageFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> sourc
     [MethodImpl(InliningOptions.ShortMethod)]
     public readonly byte GetQuantizedColor(TPixel color, out TPixel match)
     {
-        // Octree only maps the RGB component of a color
-        // so cannot tell the difference between a fully transparent
-        // pixel and a black one.
-        if (this.isDithering || color.Equals(default))
+        // Due to the addition of new colors by dithering that are not part of the original histogram,
+        // the octree nodes might not match the correct color.
+        // In this case, we must use the pixel map to get the closest color.
+        if (this.isDithering)
         {
-            return (byte)this.pixelMap!.GetClosestColor(color, out match);
+            return (byte)this.pixelMap!.GetClosestColor(color, out match, this.transparencyThreshold);
         }
 
         ref TPixel paletteRef = ref MemoryMarshal.GetReference(this.palette.Span);
-        byte index = (byte)this.octree.GetPaletteIndex(color);
-        match = Unsafe.Add(ref paletteRef, index);
-        return index;
+
+        int index = this.octree.GetPaletteIndex(color);
+        match = Unsafe.Add(ref paletteRef, (nuint)index);
+        return (byte)index;
     }
 
     /// <inheritdoc/>
@@ -155,16 +147,521 @@ public void Dispose()
             this.paletteOwner.Dispose();
             this.pixelMap?.Dispose();
             this.pixelMap = null;
+            this.octree.Dispose();
+        }
+    }
+
+    /// <summary>
+    /// A hexadecatree-based color quantization structure used for fast color distance lookups and palette generation.
+    /// This tree maintains a fixed pool of nodes (capacity 4096) where each node can have up to 16 children, stores
+    /// color accumulation data, and supports dynamic node allocation and reduction. It offers near-constant-time insertions
+    /// and lookups while consuming roughly 240 KB for the node pool.
+    /// </summary>
+    internal sealed class Octree : IDisposable
+    {
+        // Pooled buffer for OctreeNodes.
+        private readonly IMemoryOwner<OctreeNode> nodesOwner;
+
+        // Reducible nodes: one per level; we use an integer index; -1 means “no node.”
+        private readonly short[] reducibleNodes;
+
+        // Maximum number of allowable colors.
+        private readonly int maxColors;
+
+        // Maximum significant bits.
+        private readonly int maxColorBits;
+
+        // The threshold for transparent colors.
+        private readonly short transparencyThreshold;
+
+        // Instead of a reference to the root, we store the index of the root node.
+        // Index 0 is reserved for the root.
+        private readonly short rootIndex;
+
+        // Running index for node allocation. Start at 1 so that index 0 is reserved for the root.
+        private short nextNode = 1;
+
+        // Previously quantized node (index; -1 if none) and its color.
+        private int previousNode;
+        private Rgba32 previousColor;
+
+        // Free list for reclaimed node indices.
+        private readonly Stack<short> freeIndices = new();
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="Octree"/> class.
+        /// </summary>
+        /// <param name="maxColorBits">The maximum number of significant bits in the image.</param>
+        /// <param name="maxColors">The maximum number of colors to allow in the palette.</param>
+        /// <param name="transparencyThreshold">The threshold for transparent colors.</param>
+        /// <param name="allocator">The memory allocator.</param>
+        public Octree(int maxColorBits, int maxColors, short transparencyThreshold, MemoryAllocator allocator)
+        {
+            this.maxColorBits = maxColorBits;
+            this.maxColors = maxColors;
+            this.transparencyThreshold = transparencyThreshold;
+            this.Leaves = 0;
+            this.previousNode = -1;
+            this.previousColor = default;
+
+            // Allocate a conservative buffer for nodes.
+            const int capacity = 4096;
+            this.nodesOwner = allocator.Allocate<OctreeNode>(capacity, AllocationOptions.Clean);
+
+            // Create the reducible nodes array (one per level 0 .. maxColorBits-1).
+            this.reducibleNodes = new short[this.maxColorBits];
+            this.reducibleNodes.AsSpan().Fill(-1);
+
+            // Reserve index 0 for the root.
+            this.rootIndex = 0;
+            ref OctreeNode root = ref this.Nodes[this.rootIndex];
+            root.Initialize(0, this.maxColorBits, this, this.rootIndex);
+        }
+
+        /// <summary>
+        /// Gets or sets the number of leaves in the tree.
+        /// </summary>
+        public int Leaves { get; set; }
+
+        /// <summary>
+        /// Gets the full collection of nodes as a span.
+        /// </summary>
+        internal Span<OctreeNode> Nodes => this.nodesOwner.Memory.Span;
+
+        /// <summary>
+        /// Add a color to the Octree.
+        /// </summary>
+        /// <param name="color">The color to add.</param>
+        public void AddColor(Rgba32 color)
+        {
+            // Ensure that the tree is not already full.
+            if (this.nextNode >= this.Nodes.Length && this.freeIndices.Count == 0)
+            {
+                while (this.Leaves > this.maxColors)
+                {
+                    this.Reduce();
+                }
+            }
+
+            if (color.A < this.transparencyThreshold)
+            {
+                color = default;
+            }
+
+            // If the color is the same as the previous color, increment the node.
+            // Otherwise, add a new node.
+            if (this.previousColor.Equals(color))
+            {
+                if (this.previousNode == -1)
+                {
+                    this.previousColor = color;
+                    OctreeNode.AddColor(this.rootIndex, color, this.maxColorBits, 0, this);
+                }
+                else
+                {
+                    OctreeNode.Increment(this.previousNode, color, this);
+                }
+            }
+            else
+            {
+                this.previousColor = color;
+                OctreeNode.AddColor(this.rootIndex, color, this.maxColorBits, 0, this);
+            }
+        }
+
+        /// <summary>
+        /// Construct the palette from the octree.
+        /// </summary>
+        /// <param name="palette">The palette to construct.</param>
+        /// <param name="paletteIndex">The current palette index.</param>
+        public void Palettize(Span<TPixel> palette, ref short paletteIndex)
+        {
+            while (this.Leaves > this.maxColors)
+            {
+                this.Reduce();
+            }
+
+            this.Nodes[this.rootIndex].ConstructPalette(this, palette, ref paletteIndex);
+        }
+
+        /// <summary>
+        /// Get the palette index for the passed color.
+        /// </summary>
+        /// <param name="color">The color to get the palette index for.</param>
+        /// <returns>The <see cref="int"/>.</returns>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public int GetPaletteIndex(TPixel color)
+            => this.Nodes[this.rootIndex].GetPaletteIndex(color.ToRgba32(), 0, this);
+
+        /// <summary>
+        /// Track the previous node and color.
+        /// </summary>
+        /// <param name="nodeIndex">The node index.</param>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public void TrackPrevious(int nodeIndex)
+            => this.previousNode = nodeIndex;
+
+        /// <summary>
+        /// Reduce the depth of the tree.
+        /// </summary>
+        private void Reduce()
+        {
+            // Find the deepest level containing at least one reducible node
+            int index = this.maxColorBits - 1;
+            while ((index > 0) && (this.reducibleNodes[index] == -1))
+            {
+                index--;
+            }
+
+            // Reduce the node most recently added to the list at level 'index'
+            ref OctreeNode node = ref this.Nodes[this.reducibleNodes[index]];
+            this.reducibleNodes[index] = node.NextReducibleIndex;
+
+            // Decrement the leaf count after reducing the node
+            node.Reduce(this);
+
+            // And just in case I've reduced the last color to be added, and the next color to
+            // be added is the same, invalidate the previousNode...
+            this.previousNode = -1;
+        }
+
+        // Allocate a new OctreeNode from the pooled buffer.
+        // First check the freeIndices stack.
+        internal short AllocateNode()
+        {
+            if (this.freeIndices.Count > 0)
+            {
+                return this.freeIndices.Pop();
+            }
+
+            if (this.nextNode >= this.Nodes.Length)
+            {
+                return -1;
+            }
+
+            short newIndex = this.nextNode;
+            this.nextNode++;
+            return newIndex;
+        }
+
+        /// <summary>
+        /// Free a node index, making it available for re-allocation.
+        /// </summary>
+        /// <param name="index">The index to free.</param>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        internal void FreeNode(short index)
+        {
+            this.freeIndices.Push(index);
+            this.Leaves--;
+        }
+
+        /// <inheritdoc/>
+        public void Dispose() => this.nodesOwner.Dispose();
+
+        [StructLayout(LayoutKind.Sequential)]
+        internal unsafe struct OctreeNode
+        {
+            public bool Leaf;
+            public int PixelCount;
+            public int Red;
+            public int Green;
+            public int Blue;
+            public int Alpha;
+            public short PaletteIndex;
+            public short NextReducibleIndex;
+            private InlineArray16<short> children;
+
+            [UnscopedRef]
+            public Span<short> Children => this.children;
+
+            /// <summary>
+            /// Initialize the <see cref="OctreeNode"/>.
+            /// </summary>
+            /// <param name="level">The level of the node.</param>
+            /// <param name="colorBits">The number of significant color bits in the image.</param>
+            /// <param name="octree">The parent octree.</param>
+            /// <param name="index">The index of the node.</param>
+            public void Initialize(int level, int colorBits, Octree octree, short index)
+            {
+                // Construct the new node.
+                this.Leaf = level == colorBits;
+                this.Red = 0;
+                this.Green = 0;
+                this.Blue = 0;
+                this.Alpha = 0;
+                this.PixelCount = 0;
+                this.PaletteIndex = 0;
+                this.NextReducibleIndex = -1;
+
+                // Always clear the Children array.
+                this.Children.Fill(-1);
+
+                if (this.Leaf)
+                {
+                    octree.Leaves++;
+                }
+                else
+                {
+                    // Add this node to the reducible nodes list for its level.
+                    this.NextReducibleIndex = octree.reducibleNodes[level];
+                    octree.reducibleNodes[level] = index;
+                }
+            }
+
+            /// <summary>
+            /// Add a color to the Octree.
+            /// </summary>
+            /// <param name="nodeIndex">The node index.</param>
+            /// <param name="color">The color to add.</param>
+            /// <param name="colorBits">The number of significant color bits in the image.</param>
+            /// <param name="level">The level of the node.</param>
+            /// <param name="octree">The parent octree.</param>
+            public static void AddColor(int nodeIndex, Rgba32 color, int colorBits, int level, Octree octree)
+            {
+                ref OctreeNode node = ref octree.Nodes[nodeIndex];
+                if (node.Leaf)
+                {
+                    Increment(nodeIndex, color, octree);
+                    octree.TrackPrevious(nodeIndex);
+                }
+                else
+                {
+                    int index = GetColorIndex(color, level);
+                    short childIndex;
+
+                    Span<short> children = node.Children;
+                    childIndex = children[index];
+
+                    if (childIndex == -1)
+                    {
+                        childIndex = octree.AllocateNode();
+
+                        if (childIndex == -1)
+                        {
+                            // No room in the tree, so increment the count and return.
+                            Increment(nodeIndex, color, octree);
+                            octree.TrackPrevious(nodeIndex);
+                            return;
+                        }
+
+                        ref OctreeNode child = ref octree.Nodes[childIndex];
+                        child.Initialize(level + 1, colorBits, octree, childIndex);
+                        children[index] = childIndex;
+                    }
+
+                    AddColor(childIndex, color, colorBits, level + 1, octree);
+                }
+            }
+
+            /// <summary>
+            /// Increment the color components of this node.
+            /// </summary>
+            /// <param name="nodeIndex">The node index.</param>
+            /// <param name="color">The color to increment by.</param>
+            /// <param name="octree">The parent octree.</param>
+            public static void Increment(int nodeIndex, Rgba32 color, Octree octree)
+            {
+                ref OctreeNode node = ref octree.Nodes[nodeIndex];
+                node.PixelCount++;
+                node.Red += color.R;
+                node.Green += color.G;
+                node.Blue += color.B;
+                node.Alpha += color.A;
+            }
+
+            /// <summary>
+            /// Reduce this node by ensuring its children are all reduced (i.e. leaves) and then merging their data.
+            /// </summary>
+            /// <param name="octree">The parent octree.</param>
+            public void Reduce(Octree octree)
+            {
+                // If already a leaf, do nothing.
+                if (this.Leaf)
+                {
+                    return;
+                }
+
+                // Now merge the (presumably reduced) children.
+                int pixelCount = 0;
+                int sumRed = 0, sumGreen = 0, sumBlue = 0, sumAlpha = 0;
+                Span<short> children = this.Children;
+                for (int i = 0; i < children.Length; i++)
+                {
+                    short childIndex = children[i];
+                    if (childIndex != -1)
+                    {
+                        ref OctreeNode child = ref octree.Nodes[childIndex];
+                        int pixels = child.PixelCount;
+
+                        sumRed += child.Red;
+                        sumGreen += child.Green;
+                        sumBlue += child.Blue;
+                        sumAlpha += child.Alpha;
+                        pixelCount += pixels;
+
+                        // Free the child immediately.
+                        children[i] = -1;
+                        octree.FreeNode(childIndex);
+                    }
+                }
+
+                if (pixelCount > 0)
+                {
+                    this.Red = sumRed;
+                    this.Green = sumGreen;
+                    this.Blue = sumBlue;
+                    this.Alpha = sumAlpha;
+                    this.PixelCount = pixelCount;
+                }
+                else
+                {
+                    this.Red = this.Green = this.Blue = this.Alpha = 0;
+                    this.PixelCount = 0;
+                }
+
+                this.Leaf = true;
+                octree.Leaves++;
+            }
+
+            /// <summary>
+            /// Traverse the tree to construct the palette.
+            /// </summary>
+            /// <param name="octree">The parent octree.</param>
+            /// <param name="palette">The palette to construct.</param>
+            /// <param name="paletteIndex">The current palette index.</param>
+            public void ConstructPalette(Octree octree, Span<TPixel> palette, ref short paletteIndex)
+            {
+                if (this.Leaf)
+                {
+                    Vector4 sum = new(this.Red, this.Green, this.Blue, this.Alpha);
+                    Vector4 offset = new(this.PixelCount >> 1);
+                    Vector4 vector = Vector4.Clamp(
+                        (sum + offset) / this.PixelCount,
+                        Vector4.Zero,
+                        new Vector4(255));
+
+                    if (vector.W < octree.transparencyThreshold)
+                    {
+                        vector = default;
+                    }
+
+                    palette[paletteIndex] = TPixel.FromRgba32(new Rgba32((byte)vector.X, (byte)vector.Y, (byte)vector.Z, (byte)vector.W));
+
+                    this.PaletteIndex = paletteIndex++;
+                }
+                else
+                {
+                    Span<short> children = this.Children;
+                    for (int i = 0; i < children.Length; i++)
+                    {
+                        int childIndex = children[i];
+                        if (childIndex != -1)
+                        {
+                            octree.Nodes[childIndex].ConstructPalette(octree, palette, ref paletteIndex);
+                        }
+                    }
+                }
+            }
+
+            /// <summary>
+            /// Get the palette index for the passed color.
+            /// </summary>
+            /// <param name="color">The color to get the palette index for.</param>
+            /// <param name="level">The level of the node.</param>
+            /// <param name="octree">The parent octree.</param>
+            public int GetPaletteIndex(Rgba32 color, int level, Octree octree)
+            {
+                if (color.A < octree.transparencyThreshold)
+                {
+                    color = default;
+                }
+
+                if (this.Leaf)
+                {
+                    return this.PaletteIndex;
+                }
+
+                int colorIndex = GetColorIndex(color, level);
+                Span<short> children = this.Children;
+                int childIndex = children[colorIndex];
+                if (childIndex != -1)
+                {
+                    return octree.Nodes[childIndex].GetPaletteIndex(color, level + 1, octree);
+                }
+
+                for (int i = 0; i < children.Length; i++)
+                {
+                    childIndex = children[i];
+                    if (childIndex != -1)
+                    {
+                        int childPaletteIndex = octree.Nodes[childIndex].GetPaletteIndex(color, level + 1, octree);
+                        if (childPaletteIndex != -1)
+                        {
+                            return childPaletteIndex;
+                        }
+                    }
+                }
+
+                return -1;
+            }
+
+            /// <summary>
+            /// Gets the color index at the given level.
+            /// </summary>
+            /// <param name="color">The color to get the index for.</param>
+            /// <param name="level">The level to get the index at.</param>
+            public static int GetColorIndex(Rgba32 color, int level)
+            {
+                // Determine how many bits to shift based on the current tree level.
+                // At level 0, shift = 7; as level increases, the shift decreases.
+                int shift = 7 - level;
+                byte mask = (byte)(1 << shift);
+
+                // Compute the luminance of the RGB components using the BT.709 standard.
+                // This gives a measure of brightness for the color.
+                int luminance = ColorNumerics.Get8BitBT709Luminance(color.R, color.G, color.B);
+
+                // Define thresholds for determining when to include the alpha bit in the index.
+                // The thresholds are scaled according to the current level.
+                // 128 is the midpoint of the 8-bit range (0–255), so shifting it right by 'level'
+                // produces a threshold that scales with the color cube subdivision.
+                int darkThreshold = 128 >> level;
+
+                // The light threshold is set symmetrically: 255 minus the scaled midpoint.
+                int lightThreshold = 255 - (128 >> level);
+
+                // If the pixel is fully opaque and its brightness falls between the dark and light thresholds,
+                // ignore the alpha channel to maximize RGB resolution.
+                // Otherwise (if the pixel is dark, light, or semi-transparent), include the alpha bit
+                // to preserve any gradient that may be present.
+                if (color.A == 255 && luminance > darkThreshold && luminance < lightThreshold)
+                {
+                    // Extract one bit each from R, G, and B channels and combine them into a 3-bit index.
+                    int rBits = ((color.R & mask) >> shift) << 2;
+                    int gBits = ((color.G & mask) >> shift) << 1;
+                    int bBits = (color.B & mask) >> shift;
+                    return rBits | gBits | bBits;
+                }
+                else
+                {
+                    // Extract one bit from each channel including alpha (alpha becomes the most significant bit).
+                    int aBits = ((color.A & mask) >> shift) << 3;
+                    int rBits = ((color.R & mask) >> shift) << 2;
+                    int gBits = ((color.G & mask) >> shift) << 1;
+                    int bBits = (color.B & mask) >> shift;
+                    return aBits | rBits | gBits | bBits;
+                }
+            }
         }
     }
 
     /// <summary>
     /// Class which does the actual quantization.
     /// </summary>
-    private sealed class Octree
+    private sealed class Octree2
     {
         /// <summary>
-        /// The root of the Octree
+        /// The root of the Octree2
         /// </summary>
         private readonly OctreeNode root;
 
@@ -173,6 +670,11 @@ private sealed class Octree
         /// </summary>
         private readonly int maxColorBits;
 
+        /// <summary>
+        /// The threshold for transparent colors.
+        /// </summary>
+        private readonly int transparencyThreshold;
+
         /// <summary>
         /// Store the last node quantized
         /// </summary>
@@ -184,14 +686,16 @@ private sealed class Octree
         private Rgba32 previousColor;
 
         /// <summary>
-        /// Initializes a new instance of the <see cref="Octree"/> class.
+        /// Initializes a new instance of the <see cref="Octree2"/> class.
         /// </summary>
         /// <param name="maxColorBits">
         /// The maximum number of significant bits in the image
         /// </param>
-        public Octree(int maxColorBits)
+        /// <param name="transparencyThreshold">The threshold for transparent colors.</param>
+        public Octree2(int maxColorBits, int transparencyThreshold)
         {
             this.maxColorBits = maxColorBits;
+            this.transparencyThreshold = transparencyThreshold;
             this.Leaves = 0;
             this.ReducibleNodes = new OctreeNode[9];
             this.root = new OctreeNode(0, this.maxColorBits, this);
@@ -221,43 +725,46 @@ private OctreeNode?[] ReducibleNodes
         }
 
         /// <summary>
-        /// Add a given color value to the Octree
+        /// Add a given color value to the Octree2
         /// </summary>
         /// <param name="color">The color to add.</param>
         public void AddColor(Rgba32 color)
         {
+            if (color.A < this.transparencyThreshold)
+            {
+                color.A = 0;
+            }
+
             // Check if this request is for the same color as the last
             if (this.previousColor.Equals(color))
             {
                 // If so, check if I have a previous node setup.
-                // This will only occur if the first color in the image
-                // happens to be black, with an alpha component of zero.
                 if (this.previousNode is null)
                 {
                     this.previousColor = color;
-                    this.root.AddColor(ref color, this.maxColorBits, 0, this);
+                    this.root.AddColor(color, this.maxColorBits, 0, this);
                 }
                 else
                 {
                     // Just update the previous node
-                    this.previousNode.Increment(ref color);
+                    this.previousNode.Increment(color, this);
                 }
             }
             else
             {
                 this.previousColor = color;
-                this.root.AddColor(ref color, this.maxColorBits, 0, this);
+                this.root.AddColor(color, this.maxColorBits, 0, this);
             }
         }
 
         /// <summary>
-        /// Convert the nodes in the Octree to a palette with a maximum of colorCount colors
+        /// Convert the nodes in the Octree2 to a palette with a maximum of colorCount colors
         /// </summary>
         /// <param name="palette">The palette to fill.</param>
         /// <param name="colorCount">The maximum number of colors</param>
         /// <param name="paletteIndex">The palette index, used to calculate the final size of the palette.</param>
         [MethodImpl(InliningOptions.ShortMethod)]
-        public void Palletize(Span<TPixel> palette, int colorCount, ref int paletteIndex)
+        public void Palettize(Span<TPixel> palette, int colorCount, ref int paletteIndex)
         {
             while (this.Leaves > colorCount)
             {
@@ -276,10 +783,7 @@ public void Palletize(Span<TPixel> palette, int colorCount, ref int paletteIndex
         /// </returns>
         [MethodImpl(InliningOptions.ShortMethod)]
         public int GetPaletteIndex(TPixel color)
-        {
-            Rgba32 rgba = color.ToRgba32();
-            return this.root.GetPaletteIndex(ref rgba, 0);
-        }
+            => this.root.GetPaletteIndex(color.ToRgba32(), 0);
 
         /// <summary>
         /// Keep track of the previous node that was quantized
@@ -307,7 +811,7 @@ private void Reduce()
             this.ReducibleNodes[index] = node.NextReducible;
 
             // Decrement the leaf count after reducing the node
-            this.Leaves -= node.Reduce();
+            this.Leaves -= node.Reduce(this);
 
             // And just in case I've reduced the last color to be added, and the next color to
             // be added is the same, invalidate the previousNode...
@@ -349,6 +853,11 @@ public sealed class OctreeNode
             /// </summary>
             private int blue;
 
+            /// <summary>
+            /// Alpha component
+            /// </summary>
+            private int alpha;
+
             /// <summary>
             /// The index of this node in the palette
             /// </summary>
@@ -360,12 +869,12 @@ public sealed class OctreeNode
             /// <param name="level">The level in the tree = 0 - 7.</param>
             /// <param name="colorBits">The number of significant color bits in the image.</param>
             /// <param name="octree">The tree to which this node belongs.</param>
-            public OctreeNode(int level, int colorBits, Octree octree)
+            public OctreeNode(int level, int colorBits, Octree2 octree)
             {
                 // Construct the new node
                 this.leaf = level == colorBits;
 
-                this.red = this.green = this.blue = 0;
+                this.red = this.green = this.blue = this.alpha = 0;
                 this.pixelCount = 0;
 
                 // If a leaf, increment the leaf count
@@ -380,7 +889,7 @@ public OctreeNode(int level, int colorBits, Octree octree)
                     // Otherwise add this to the reducible nodes
                     this.NextReducible = octree.ReducibleNodes[level];
                     octree.ReducibleNodes[level] = this;
-                    this.children = new OctreeNode[8];
+                    this.children = new OctreeNode[16];
                 }
             }
 
@@ -400,12 +909,12 @@ public OctreeNode? NextReducible
             /// <param name="colorBits">The number of significant color bits.</param>
             /// <param name="level">The level in the tree.</param>
             /// <param name="octree">The tree to which this node belongs.</param>
-            public void AddColor(ref Rgba32 color, int colorBits, int level, Octree octree)
+            public void AddColor(Rgba32 color, int colorBits, int level, Octree2 octree)
             {
                 // Update the color information if this is a leaf
                 if (this.leaf)
                 {
-                    this.Increment(ref color);
+                    this.Increment(color, octree);
 
                     // Setup the previous node
                     octree.TrackPrevious(this);
@@ -413,7 +922,7 @@ public void AddColor(ref Rgba32 color, int colorBits, int level, Octree octree)
                 else
                 {
                     // Go to the next level down in the tree
-                    int index = GetColorIndex(ref color, level);
+                    int index = GetColorIndex(color, level);
 
                     OctreeNode? child = this.children![index];
                     if (child is null)
@@ -424,38 +933,63 @@ public void AddColor(ref Rgba32 color, int colorBits, int level, Octree octree)
                     }
 
                     // Add the color to the child node
-                    child.AddColor(ref color, colorBits, level + 1, octree);
+                    child.AddColor(color, colorBits, level + 1, octree);
                 }
             }
 
             /// <summary>
-            /// Reduce this node by removing all of its children
+            /// Reduce this node by removing all of its children.
             /// </summary>
             /// <returns>The number of leaves removed</returns>
-            public int Reduce()
+            /// <param name="octree">The tree to which this node belongs.</param>
+            public int Reduce(Octree2 octree)
             {
-                this.red = this.green = this.blue = 0;
+                if (this.leaf)
+                {
+                    return 1;
+                }
+
                 int childNodes = 0;
+                int sumRed = 0, sumGreen = 0, sumBlue = 0, sumAlpha = 0, pixelCount = 0;
 
-                // Loop through all children and add their information to this node
-                for (int index = 0; index < 8; index++)
+                // Loop through all children.
+                for (int index = 0; index < this.children!.Length; index++)
                 {
-                    OctreeNode? child = this.children![index];
+                    OctreeNode? child = this.children[index];
                     if (child != null)
                     {
-                        this.red += child.red;
-                        this.green += child.green;
-                        this.blue += child.blue;
-                        this.pixelCount += child.pixelCount;
-                        ++childNodes;
+                        childNodes++;
+
+                        sumRed += child.red;
+                        sumGreen += child.green;
+                        sumBlue += child.blue;
+                        sumAlpha += child.alpha;
+                        pixelCount += child.pixelCount;
+
+                        // Remove the child reference.
                         this.children[index] = null;
                     }
                 }
 
-                // Now change this to a leaf node
+                if (pixelCount > 0)
+                {
+                    int offset = pixelCount >> 1;
+                    this.red = sumRed;
+                    this.green = sumGreen;
+                    this.blue = sumBlue;
+                    this.alpha = ((sumAlpha + offset) / pixelCount < octree.transparencyThreshold) ? 0 : sumAlpha;
+                    this.pixelCount = pixelCount;
+                }
+                else
+                {
+                    this.red = this.green = this.blue = this.alpha = 0;
+                    this.pixelCount = 0;
+                }
+
+                // Convert this node into a leaf.
                 this.leaf = true;
 
-                // Return the number of nodes to decrement the leaf count by
+                // Return the number of nodes merged (for decrementing the leaf count).
                 return childNodes - 1;
             }
 
@@ -470,12 +1004,15 @@ public void ConstructPalette(Span<TPixel> palette, ref int index)
                 if (this.leaf)
                 {
                     // Set the color of the palette entry
-                    Vector3 vector = Vector3.Clamp(
-                        new Vector3(this.red, this.green, this.blue) / this.pixelCount,
-                        Vector3.Zero,
-                        new Vector3(255));
+                    Vector4 sum = new(this.red, this.green, this.blue, this.alpha);
+                    Vector4 offset = new(this.pixelCount >> 1);
+
+                    Vector4 vector = Vector4.Clamp(
+                        (sum + offset) / this.pixelCount,
+                        Vector4.Zero,
+                        new Vector4(255));
 
-                    palette[index] = TPixel.FromRgba32(new Rgba32((byte)vector.X, (byte)vector.Y, (byte)vector.Z));
+                    palette[index] = TPixel.FromRgba32(new Rgba32((byte)vector.X, (byte)vector.Y, (byte)vector.Z, (byte)vector.W));
 
                     // Consume the next palette index
                     this.paletteIndex = index++;
@@ -483,9 +1020,9 @@ public void ConstructPalette(Span<TPixel> palette, ref int index)
                 else
                 {
                     // Loop through children looking for leaves
-                    for (int i = 0; i < 8; i++)
+                    for (int i = 0; i < this.children!.Length; i++)
                     {
-                        this.children![i]?.ConstructPalette(palette, ref index);
+                        this.children[i]?.ConstructPalette(palette, ref index);
                     }
                 }
             }
@@ -499,20 +1036,20 @@ public void ConstructPalette(Span<TPixel> palette, ref int index)
             /// The <see cref="int"/> representing the index of the pixel in the palette.
             /// </returns>
             [MethodImpl(InliningOptions.ColdPath)]
-            public int GetPaletteIndex(ref Rgba32 pixel, int level)
+            public int GetPaletteIndex(Rgba32 pixel, int level)
             {
                 if (this.leaf)
                 {
                     return this.paletteIndex;
                 }
 
-                int colorIndex = GetColorIndex(ref pixel, level);
+                int colorIndex = GetColorIndex(pixel, level);
                 OctreeNode? child = this.children![colorIndex];
 
-                int index = 0;
+                int index = -1;
                 if (child != null)
                 {
-                    index = child.GetPaletteIndex(ref pixel, level + 1);
+                    index = child.GetPaletteIndex(pixel, level + 1);
                 }
                 else
                 {
@@ -522,8 +1059,8 @@ public int GetPaletteIndex(ref Rgba32 pixel, int level)
                         child = this.children[i];
                         if (child != null)
                         {
-                            int childIndex = child.GetPaletteIndex(ref pixel, level + 1);
-                            if (childIndex != 0)
+                            int childIndex = child.GetPaletteIndex(pixel, level + 1);
+                            if (childIndex != -1)
                             {
                                 return childIndex;
                             }
@@ -541,27 +1078,54 @@ public int GetPaletteIndex(ref Rgba32 pixel, int level)
             /// <param name="level">The node level.</param>
             /// <returns>The <see cref="int"/> index.</returns>
             [MethodImpl(InliningOptions.ShortMethod)]
-            private static int GetColorIndex(ref Rgba32 color, int level)
+            private static int GetColorIndex(Rgba32 color, int level)
             {
                 int shift = 7 - level;
                 byte mask = (byte)(1 << shift);
 
-                return ((color.R & mask) >> shift)
-                    | (((color.G & mask) >> shift) << 1)
-                    | (((color.B & mask) >> shift) << 2);
+                // Compute luminance of the RGB channels.
+                int luminance = ColorNumerics.Get8BitBT709Luminance(color.R, color.G, color.B);
+
+                // Shift the threshold (arbitrary) right by the current level.
+                // This allows us to partition the RGB space into smaller and smaller cubes
+                // with increasing accuracy for the alpha component.
+                int darkThreshold = 24 >> level;
+
+                // For fully opaque and bright pixels, ignore the alpha bit to achieve finer RGB partitioning.
+                // For dark pixels, include the alpha bit so that dark drop shadows remain distinct.
+                if (color.A == 255 && luminance > darkThreshold)
+                {
+                    int rBits = ((color.R & mask) >> shift) << 2;
+                    int gBits = ((color.G & mask) >> shift) << 1;
+                    int bBits = (color.B & mask) >> shift;
+                    return rBits | gBits | bBits;
+                }
+                else
+                {
+                    int aBits = ((color.A & mask) >> shift) << 3;
+                    int rBits = ((color.R & mask) >> shift) << 2;
+                    int gBits = ((color.G & mask) >> shift) << 1;
+                    int bBits = (color.B & mask) >> shift;
+                    return aBits | rBits | gBits | bBits;
+                }
             }
 
             /// <summary>
             /// Increment the color count and add to the color information
             /// </summary>
             /// <param name="color">The pixel to add.</param>
+            /// <param name="octree">The parent octree.</param>
             [MethodImpl(InliningOptions.ShortMethod)]
-            public void Increment(ref Rgba32 color)
+            public void Increment(Rgba32 color, Octree2 octree)
             {
                 this.pixelCount++;
                 this.red += color.R;
                 this.green += color.G;
                 this.blue += color.B;
+
+                int sumAlpha = this.alpha + color.A;
+                int offset = this.pixelCount >> 1;
+                this.alpha = ((sumAlpha + offset) / this.pixelCount < octree.transparencyThreshold) ? 0 : sumAlpha;
             }
         }
     }
diff --git a/src/ImageSharp/Processing/Processors/Quantization/PaletteQuantizer.cs b/src/ImageSharp/Processing/Processors/Quantization/PaletteQuantizer.cs
index 13a59a26de..a49691515a 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/PaletteQuantizer.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/PaletteQuantizer.cs
@@ -11,7 +11,8 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization;
 public class PaletteQuantizer : IQuantizer
 {
     private readonly ReadOnlyMemory<Color> colorPalette;
-    private readonly int transparentIndex;
+    private readonly int transparencyIndex;
+    private readonly Color transparentColor;
 
     /// <summary>
     /// Initializes a new instance of the <see cref="PaletteQuantizer"/> class.
@@ -25,27 +26,33 @@ public PaletteQuantizer(ReadOnlyMemory<Color> palette)
     /// <summary>
     /// Initializes a new instance of the <see cref="PaletteQuantizer"/> class.
     /// </summary>
-    /// <param name="palette">The color palette.</param>
+    /// <param name="palette">The color palette to use.</param>
     /// <param name="options">The quantizer options defining quantization rules.</param>
     public PaletteQuantizer(ReadOnlyMemory<Color> palette, QuantizerOptions options)
-        : this(palette, options, -1)
+        : this(palette, options, -1, default)
     {
     }
 
     /// <summary>
     /// Initializes a new instance of the <see cref="PaletteQuantizer"/> class.
     /// </summary>
-    /// <param name="palette">The color palette.</param>
+    /// <param name="palette">The color palette to use.</param>
     /// <param name="options">The quantizer options defining quantization rules.</param>
-    /// <param name="transparentIndex">An explicit index at which to match transparent pixels.</param>
-    internal PaletteQuantizer(ReadOnlyMemory<Color> palette, QuantizerOptions options, int transparentIndex)
+    /// <param name="transparencyIndex">The index of the color in the palette that should be considered as transparent.</param>
+    /// <param name="transparentColor">The color that should be considered as transparent.</param>
+    internal PaletteQuantizer(
+        ReadOnlyMemory<Color> palette,
+        QuantizerOptions options,
+        int transparencyIndex,
+        Color transparentColor)
     {
         Guard.MustBeGreaterThan(palette.Length, 0, nameof(palette));
         Guard.NotNull(options, nameof(options));
 
         this.colorPalette = palette;
         this.Options = options;
-        this.transparentIndex = transparentIndex;
+        this.transparencyIndex = transparencyIndex;
+        this.transparentColor = transparentColor;
     }
 
     /// <inheritdoc />
@@ -66,6 +73,6 @@ public IQuantizer<TPixel> CreatePixelSpecificQuantizer<TPixel>(Configuration con
         // treat the buffer as FILO.
         TPixel[] palette = new TPixel[Math.Min(options.MaxColors, this.colorPalette.Length)];
         Color.ToPixel(this.colorPalette.Span[..palette.Length], palette.AsSpan());
-        return new PaletteQuantizer<TPixel>(configuration, options, palette, this.transparentIndex);
+        return new PaletteQuantizer<TPixel>(configuration, options, palette, this.transparencyIndex, this.transparentColor.ToPixel<TPixel>());
     }
 }
diff --git a/src/ImageSharp/Processing/Processors/Quantization/PaletteQuantizer{TPixel}.cs b/src/ImageSharp/Processing/Processors/Quantization/PaletteQuantizer{TPixel}.cs
index 092975d28a..d734b36c30 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/PaletteQuantizer{TPixel}.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/PaletteQuantizer{TPixel}.cs
@@ -17,10 +17,12 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization;
     "Design",
     "CA1001:Types that own disposable fields should be disposable",
     Justification = "https://github.com/dotnet/roslyn-analyzers/issues/6151")]
-internal readonly struct PaletteQuantizer<TPixel> : IQuantizer<TPixel>
+internal struct PaletteQuantizer<TPixel> : IQuantizer<TPixel>
     where TPixel : unmanaged, IPixel<TPixel>
 {
     private readonly EuclideanPixelMap<TPixel> pixelMap;
+    private int transparencyIndex;
+    private TPixel transparentColor;
 
     /// <summary>
     /// Initializes a new instance of the <see cref="PaletteQuantizer{TPixel}"/> struct.
@@ -28,20 +30,37 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization;
     /// <param name="configuration">The configuration which allows altering default behavior or extending the library.</param>
     /// <param name="options">The quantizer options defining quantization rules.</param>
     /// <param name="palette">The palette to use.</param>
-    /// <param name="transparentIndex">An explicit index at which to match transparent pixels.</param>
     [MethodImpl(InliningOptions.ShortMethod)]
+    public PaletteQuantizer(Configuration configuration, QuantizerOptions options, ReadOnlyMemory<TPixel> palette)
+        : this(configuration, options, palette, -1, default)
+    {
+        Guard.NotNull(configuration, nameof(configuration));
+        Guard.NotNull(options, nameof(options));
+    }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="PaletteQuantizer{TPixel}"/> struct.
+    /// </summary>
+    /// <param name="configuration">The configuration which allows altering default behavior or extending the library.</param>
+    /// <param name="options">The quantizer options defining quantization rules.</param>
+    /// <param name="palette">The palette to use.</param>
+    /// <param name="transparencyIndex">The index of the color in the palette that should be considered as transparent.</param>
+    /// <param name="transparentColor">The color that should be considered as transparent.</param>
     public PaletteQuantizer(
         Configuration configuration,
         QuantizerOptions options,
         ReadOnlyMemory<TPixel> palette,
-        int transparentIndex)
+        int transparencyIndex,
+        TPixel transparentColor)
     {
         Guard.NotNull(configuration, nameof(configuration));
         Guard.NotNull(options, nameof(options));
 
         this.Configuration = configuration;
         this.Options = options;
-        this.pixelMap = new EuclideanPixelMap<TPixel>(configuration, palette, transparentIndex);
+        this.pixelMap = new EuclideanPixelMap<TPixel>(configuration, palette);
+        this.transparencyIndex = transparencyIndex;
+        this.transparentColor = transparentColor;
     }
 
     /// <inheritdoc/>
@@ -51,7 +70,7 @@ public PaletteQuantizer(
     public QuantizerOptions Options { get; }
 
     /// <inheritdoc/>
-    public ReadOnlyMemory<TPixel> Palette => this.pixelMap.Palette;
+    public readonly ReadOnlyMemory<TPixel> Palette => this.pixelMap.Palette;
 
     /// <inheritdoc/>
     [MethodImpl(InliningOptions.ShortMethod)]
@@ -60,21 +79,29 @@ public readonly IndexedImageFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> sourc
 
     /// <inheritdoc/>
     [MethodImpl(InliningOptions.ShortMethod)]
-    public void AddPaletteColors(Buffer2DRegion<TPixel> pixelRegion)
+    public readonly void AddPaletteColors(in Buffer2DRegion<TPixel> pixelRegion)
     {
     }
 
-    /// <summary>
-    /// Allows setting the transparent index after construction.
-    /// </summary>
-    /// <param name="index">An explicit index at which to match transparent pixels.</param>
-    public void SetTransparentIndex(int index) => this.pixelMap.SetTransparentIndex(index);
-
     /// <inheritdoc/>
     [MethodImpl(InliningOptions.ShortMethod)]
     public readonly byte GetQuantizedColor(TPixel color, out TPixel match)
-        => (byte)this.pixelMap.GetClosestColor(color, out match);
+    {
+        if (this.transparencyIndex >= 0 && color.Equals(this.transparentColor))
+        {
+            match = this.transparentColor;
+            return (byte)this.transparencyIndex;
+        }
+
+        return (byte)this.pixelMap.GetClosestColor(color, out match);
+    }
+
+    public void SetTransparencyIndex(int transparencyIndex, TPixel transparentColor)
+    {
+        this.transparencyIndex = transparencyIndex;
+        this.transparentColor = transparentColor;
+    }
 
     /// <inheritdoc/>
-    public void Dispose() => this.pixelMap.Dispose();
+    public readonly void Dispose() => this.pixelMap.Dispose();
 }
diff --git a/src/ImageSharp/Processing/Processors/Quantization/QuantizerConstants.cs b/src/ImageSharp/Processing/Processors/Quantization/QuantizerConstants.cs
index 2bf4c6d56d..3b515e372d 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/QuantizerConstants.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/QuantizerConstants.cs
@@ -21,15 +21,30 @@ public static class QuantizerConstants
     public const int MaxColors = 256;
 
     /// <summary>
-    /// The minumim dithering scale used to adjust the amount of dither.
+    /// The minimum dithering scale used to adjust the amount of dither.
     /// </summary>
     public const float MinDitherScale = 0;
 
     /// <summary>
-    /// The max dithering scale used to adjust the amount of dither.
+    /// The maximum dithering scale used to adjust the amount of dither.
     /// </summary>
     public const float MaxDitherScale = 1F;
 
+    /// <summary>
+    /// The default threshold at which to consider a pixel transparent.
+    /// </summary>
+    public const float DefaultTransparencyThreshold = 64 / 255F;
+
+    /// <summary>
+    /// The minimum threshold at which to consider a pixel transparent.
+    /// </summary>
+    public const float MinTransparencyThreshold = 0F;
+
+    /// <summary>
+    /// The maximum threshold at which to consider a pixel transparent.
+    /// </summary>
+    public const float MaxTransparencyThreshold = 1F;
+
     /// <summary>
     /// Gets the default dithering algorithm to use.
     /// </summary>
diff --git a/src/ImageSharp/Processing/Processors/Quantization/QuantizerOptions.cs b/src/ImageSharp/Processing/Processors/Quantization/QuantizerOptions.cs
index a6bb265a81..4f4104a8a3 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/QuantizerOptions.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/QuantizerOptions.cs
@@ -12,6 +12,7 @@ public class QuantizerOptions
 {
     private float ditherScale = QuantizerConstants.MaxDitherScale;
     private int maxColors = QuantizerConstants.MaxColors;
+    private float threshold = QuantizerConstants.DefaultTransparencyThreshold;
 
     /// <summary>
     /// Gets or sets the  algorithm to apply to the output image.
@@ -38,4 +39,14 @@ public int MaxColors
         get => this.maxColors;
         set => this.maxColors = Numerics.Clamp(value, QuantizerConstants.MinColors, QuantizerConstants.MaxColors);
     }
+
+    /// <summary>
+    /// Gets or sets the threshold at which to consider a pixel transparent. Range 0..1.
+    /// Defaults to <see cref="QuantizerConstants.DefaultTransparencyThreshold"/>.
+    /// </summary>
+    public float TransparencyThreshold
+    {
+        get => this.threshold;
+        set => this.threshold = Numerics.Clamp(value, QuantizerConstants.MinTransparencyThreshold, QuantizerConstants.MaxTransparencyThreshold);
+    }
 }
diff --git a/src/ImageSharp/Processing/Processors/Quantization/QuantizerUtilities.cs b/src/ImageSharp/Processing/Processors/Quantization/QuantizerUtilities.cs
index 6d2200b8a7..7669f0d3c6 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/QuantizerUtilities.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/QuantizerUtilities.cs
@@ -112,7 +112,12 @@ public static void BuildPalette<TPixel>(
         IPixelSamplingStrategy pixelSamplingStrategy,
         Image<TPixel> source)
         where TPixel : unmanaged, IPixel<TPixel>
-        => quantizer.BuildPalette(source.Configuration, TransparentColorMode.Preserve, pixelSamplingStrategy, source);
+        => quantizer.BuildPalette(
+            source.Configuration,
+            TransparentColorMode.Preserve,
+            pixelSamplingStrategy,
+            source,
+            Color.Transparent);
 
     /// <summary>
     /// Adds colors to the quantized palette from the given pixel regions.
@@ -123,27 +128,33 @@ public static void BuildPalette<TPixel>(
     /// <param name="mode">The transparent color mode.</param>
     /// <param name="pixelSamplingStrategy">The pixel sampling strategy.</param>
     /// <param name="source">The source image to sample from.</param>
+    /// <param name="backgroundColor">The background color to use when clearing transparent pixels.</param>
     public static void BuildPalette<TPixel>(
         this IQuantizer<TPixel> quantizer,
         Configuration configuration,
         TransparentColorMode mode,
         IPixelSamplingStrategy pixelSamplingStrategy,
-        Image<TPixel> source)
+        Image<TPixel> source,
+        Color backgroundColor)
         where TPixel : unmanaged, IPixel<TPixel>
     {
         if (EncodingUtilities.ShouldClearTransparentPixels<TPixel>(mode))
         {
             foreach (Buffer2DRegion<TPixel> region in pixelSamplingStrategy.EnumeratePixelRegions(source))
             {
+                // We need to clone the region to ensure we don't alter the original image.
                 using Buffer2D<TPixel> clone = region.Buffer.CloneRegion(configuration, region.Rectangle);
-                quantizer.AddPaletteColors(clone.GetRegion());
+                Buffer2DRegion<TPixel> clonedRegion = clone.GetRegion();
+
+                EncodingUtilities.ClearTransparentPixels(configuration, in clonedRegion, backgroundColor);
+                quantizer.AddPaletteColors(in clonedRegion);
             }
         }
         else
         {
             foreach (Buffer2DRegion<TPixel> region in pixelSamplingStrategy.EnumeratePixelRegions(source))
             {
-                quantizer.AddPaletteColors(region);
+                quantizer.AddPaletteColors(in region);
             }
         }
     }
@@ -160,7 +171,12 @@ public static void BuildPalette<TPixel>(
         IPixelSamplingStrategy pixelSamplingStrategy,
         ImageFrame<TPixel> source)
         where TPixel : unmanaged, IPixel<TPixel>
-        => quantizer.BuildPalette(source.Configuration, TransparentColorMode.Preserve, pixelSamplingStrategy, source);
+        => quantizer.BuildPalette(
+            source.Configuration,
+            TransparentColorMode.Preserve,
+            pixelSamplingStrategy,
+            source,
+            Color.Transparent);
 
     /// <summary>
     /// Adds colors to the quantized palette from the given pixel regions.
@@ -171,27 +187,33 @@ public static void BuildPalette<TPixel>(
     /// <param name="mode">The transparent color mode.</param>
     /// <param name="pixelSamplingStrategy">The pixel sampling strategy.</param>
     /// <param name="source">The source image frame to sample from.</param>
+    /// <param name="backgroundColor">The background color to use when clearing transparent pixels.</param>
     public static void BuildPalette<TPixel>(
         this IQuantizer<TPixel> quantizer,
         Configuration configuration,
         TransparentColorMode mode,
         IPixelSamplingStrategy pixelSamplingStrategy,
-        ImageFrame<TPixel> source)
+        ImageFrame<TPixel> source,
+        Color backgroundColor)
         where TPixel : unmanaged, IPixel<TPixel>
     {
         if (EncodingUtilities.ShouldClearTransparentPixels<TPixel>(mode))
         {
+            // We need to clone the region to ensure we don't alter the original image.
             foreach (Buffer2DRegion<TPixel> region in pixelSamplingStrategy.EnumeratePixelRegions(source))
             {
                 using Buffer2D<TPixel> clone = region.Buffer.CloneRegion(configuration, region.Rectangle);
-                quantizer.AddPaletteColors(clone.GetRegion());
+                Buffer2DRegion<TPixel> clonedRegion = clone.GetRegion();
+
+                EncodingUtilities.ClearTransparentPixels(configuration, in clonedRegion, backgroundColor);
+                quantizer.AddPaletteColors(in clonedRegion);
             }
         }
         else
         {
             foreach (Buffer2DRegion<TPixel> region in pixelSamplingStrategy.EnumeratePixelRegions(source))
             {
-                quantizer.AddPaletteColors(region);
+                quantizer.AddPaletteColors(in region);
             }
         }
     }
diff --git a/src/ImageSharp/Processing/Processors/Quantization/WuQuantizer{TPixel}.cs b/src/ImageSharp/Processing/Processors/Quantization/WuQuantizer{TPixel}.cs
index ba2ab825ad..e637c2cf04 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/WuQuantizer{TPixel}.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/WuQuantizer{TPixel}.cs
@@ -74,6 +74,7 @@ internal struct WuQuantizer<TPixel> : IQuantizer<TPixel>
     private readonly IMemoryOwner<TPixel> paletteOwner;
     private ReadOnlyMemory<TPixel> palette;
     private int maxColors;
+    private short transparencyThreshold;
     private readonly Box[] colorCube;
     private EuclideanPixelMap<TPixel>? pixelMap;
     private readonly bool isDithering;
@@ -102,6 +103,7 @@ public WuQuantizer(Configuration configuration, QuantizerOptions options)
         this.pixelMap = default;
         this.palette = default;
         this.isDithering = this.isDithering = this.Options.Dither is not null;
+        this.transparencyThreshold = (short)(this.Options.TransparencyThreshold * 255);
     }
 
     /// <inheritdoc/>
@@ -111,57 +113,57 @@ public WuQuantizer(Configuration configuration, QuantizerOptions options)
     public QuantizerOptions Options { get; }
 
     /// <inheritdoc/>
-    public readonly ReadOnlyMemory<TPixel> Palette
+    public ReadOnlyMemory<TPixel> Palette
     {
         get
         {
-            QuantizerUtilities.CheckPaletteState(in this.palette);
+            if (this.palette.IsEmpty)
+            {
+                this.ResolvePalette();
+                QuantizerUtilities.CheckPaletteState(in this.palette);
+            }
+
             return this.palette;
         }
     }
 
     /// <inheritdoc/>
-    public void AddPaletteColors(Buffer2DRegion<TPixel> pixelRegion)
+    public readonly void AddPaletteColors(in Buffer2DRegion<TPixel> pixelRegion)
+        => this.Build3DHistogram(pixelRegion);
+
+    /// <summary>
+    /// Once all histogram data has been accumulated, this method computes the moments,
+    /// splits the color cube, and resolves the final palette from the accumulated histogram.
+    /// </summary>
+    private void ResolvePalette()
     {
-        // TODO: Something is destroying the existing palette when adding new colors.
-        // When the QuantizingImageEncoder.PixelSamplingStrategy is DefaultPixelSamplingStrategy
-        // this leads to performance issues + the palette is not preserved.
-        // https://github.com/SixLabors/ImageSharp/issues/2498
-        this.Build3DHistogram(pixelRegion);
+        // Calculate the cumulative moments from the accumulated histogram.
         this.Get3DMoments(this.memoryAllocator);
+
+        // Partition the histogram into color cubes.
         this.BuildCube();
 
-        // Slice again since maxColors has been updated since the buffer was created.
+        // Compute the palette colors from the resolved cubes.
         Span<TPixel> paletteSpan = this.paletteOwner.GetSpan()[..this.maxColors];
         ReadOnlySpan<Moment> momentsSpan = this.momentsOwner.GetSpan();
         for (int k = 0; k < paletteSpan.Length; k++)
         {
             this.Mark(ref this.colorCube[k], (byte)k);
-
             Moment moment = Volume(ref this.colorCube[k], momentsSpan);
-
             if (moment.Weight > 0)
             {
                 paletteSpan[k] = TPixel.FromScaledVector4(moment.Normalize());
             }
         }
 
-        ReadOnlyMemory<TPixel> result = this.paletteOwner.Memory[..paletteSpan.Length];
-        if (this.isDithering)
+        // Update the palette to the new computed colors.
+        this.palette = this.paletteOwner.Memory[..paletteSpan.Length];
+
+        // Create the pixel map if dithering is enabled.
+        if (this.isDithering && this.pixelMap is null)
         {
-            // When called multiple times by QuantizerUtilities.BuildPalette
-            // this prevents memory churn caused by reallocation.
-            if (this.pixelMap is null)
-            {
-                this.pixelMap = new EuclideanPixelMap<TPixel>(this.Configuration, result);
-            }
-            else
-            {
-                this.pixelMap.Clear(result);
-            }
+            this.pixelMap = new EuclideanPixelMap<TPixel>(this.Configuration, this.palette);
         }
-
-        this.palette = result;
     }
 
     /// <inheritdoc/>
@@ -172,12 +174,19 @@ public readonly IndexedImageFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> sourc
     /// <inheritdoc/>
     public readonly byte GetQuantizedColor(TPixel color, out TPixel match)
     {
+        // Due to the addition of new colors by dithering that are not part of the original histogram,
+        // the color cube might not match the correct color.
+        // In this case, we must use the pixel map to get the closest color.
         if (this.isDithering)
         {
-            return (byte)this.pixelMap!.GetClosestColor(color, out match);
+            return (byte)this.pixelMap!.GetClosestColor(color, out match, this.transparencyThreshold);
         }
 
         Rgba32 rgba = color.ToRgba32();
+        if (rgba.A < this.transparencyThreshold)
+        {
+            rgba = default;
+        }
 
         const int shift = 8 - IndexBits;
         int r = rgba.R >> shift;
@@ -188,7 +197,7 @@ public readonly byte GetQuantizedColor(TPixel color, out TPixel match)
         ReadOnlySpan<byte> tagSpan = this.tagsOwner.GetSpan();
         byte index = tagSpan[GetPaletteIndex(r + 1, g + 1, b + 1, a + 1)];
         ref TPixel paletteRef = ref MemoryMarshal.GetReference(this.palette.Span);
-        match = Unsafe.Add(ref paletteRef, index);
+        match = Unsafe.Add(ref paletteRef, (nuint)index);
         return index;
     }
 
@@ -360,7 +369,7 @@ private static Moment Top(ref Box cube, int direction, int position, ReadOnlySpa
     /// Builds a 3-D color histogram of <c>counts, r/g/b, c^2</c>.
     /// </summary>
     /// <param name="source">The source pixel data.</param>
-    private readonly void Build3DHistogram(Buffer2DRegion<TPixel> source)
+    private readonly void Build3DHistogram(in Buffer2DRegion<TPixel> source)
     {
         Span<Moment> momentSpan = this.momentsOwner.GetSpan();
 
@@ -368,6 +377,8 @@ private readonly void Build3DHistogram(Buffer2DRegion<TPixel> source)
         using IMemoryOwner<Rgba32> buffer = this.memoryAllocator.Allocate<Rgba32>(source.Width);
         Span<Rgba32> bufferSpan = buffer.GetSpan();
 
+        float transparencyThreshold = this.Options.TransparencyThreshold * 255;
+
         for (int y = 0; y < source.Height; y++)
         {
             Span<TPixel> row = source.DangerousGetRowSpan(y);
@@ -376,6 +387,10 @@ private readonly void Build3DHistogram(Buffer2DRegion<TPixel> source)
             for (int x = 0; x < bufferSpan.Length; x++)
             {
                 Rgba32 rgba = bufferSpan[x];
+                if (rgba.A < transparencyThreshold)
+                {
+                    rgba = default;
+                }
 
                 int r = (rgba.R >> (8 - IndexBits)) + 1;
                 int g = (rgba.G >> (8 - IndexBits)) + 1;
diff --git a/src/ImageSharp/Processing/Processors/Transforms/TransformProcessor{TPixel}.cs b/src/ImageSharp/Processing/Processors/Transforms/TransformProcessor{TPixel}.cs
index bdfac00366..a8455a06ea 100644
--- a/src/ImageSharp/Processing/Processors/Transforms/TransformProcessor{TPixel}.cs
+++ b/src/ImageSharp/Processing/Processors/Transforms/TransformProcessor{TPixel}.cs
@@ -3,6 +3,7 @@
 
 using SixLabors.ImageSharp.PixelFormats;
 
+// TODO: DO we need this class?
 namespace SixLabors.ImageSharp.Processing.Processors.Transforms;
 
 /// <summary>
@@ -22,18 +23,4 @@ protected TransformProcessor(Configuration configuration, Image<TPixel> source,
         : base(configuration, source, sourceRectangle)
     {
     }
-
-    /// <inheritdoc/>
-    protected override void AfterFrameApply(ImageFrame<TPixel> source, ImageFrame<TPixel> destination)
-    {
-        base.AfterFrameApply(source, destination);
-        destination.Metadata.AfterFrameApply(source, destination);
-    }
-
-    /// <inheritdoc/>
-    protected override void AfterImageApply(Image<TPixel> destination)
-    {
-        base.AfterImageApply(destination);
-        destination.Metadata.AfterImageApply(destination);
-    }
 }
diff --git a/tests/ImageSharp.Tests/Formats/Gif/GifEncoderTests.cs b/tests/ImageSharp.Tests/Formats/Gif/GifEncoderTests.cs
index f12f66186e..d219f551b2 100644
--- a/tests/ImageSharp.Tests/Formats/Gif/GifEncoderTests.cs
+++ b/tests/ImageSharp.Tests/Formats/Gif/GifEncoderTests.cs
@@ -419,4 +419,15 @@ public void Encode_WithTransparentColorBehaviorClear_Works()
             }
         });
     }
+
+    [Theory]
+    [WithFile(TestImages.Gif.Issues.Issue2866, PixelTypes.Rgba32)]
+    public void GifEncoder_CanDecode_Issue2866<TPixel>(TestImageProvider<TPixel> provider)
+    where TPixel : unmanaged, IPixel<TPixel>
+    {
+        using Image<TPixel> image = provider.GetImage();
+
+        // image.DebugSaveMultiFrame(provider);
+        provider.Utility.SaveTestOutputFile(image, "gif", new GifEncoder(), "animated");
+    }
 }
diff --git a/tests/ImageSharp.Tests/Formats/Png/PngEncoderTests.cs b/tests/ImageSharp.Tests/Formats/Png/PngEncoderTests.cs
index b4995d77b6..298d5b788e 100644
--- a/tests/ImageSharp.Tests/Formats/Png/PngEncoderTests.cs
+++ b/tests/ImageSharp.Tests/Formats/Png/PngEncoderTests.cs
@@ -442,11 +442,12 @@ public void Encode_APng<TPixel>(TestImageProvider<TPixel> provider)
     }
 
     [Theory]
-    [WithFile(TestImages.Gif.Leo, PixelTypes.Rgba32)]
-    public void Encode_AnimatedFormatTransform_FromGif<TPixel>(TestImageProvider<TPixel> provider)
+    [WithFile(TestImages.Gif.Leo, PixelTypes.Rgba32, 0.613F)]
+    [WithFile(TestImages.Gif.Issues.Issue2866, PixelTypes.Rgba32, 1.06F)]
+    public void Encode_AnimatedFormatTransform_FromGif<TPixel>(TestImageProvider<TPixel> provider, float percentage)
         where TPixel : unmanaged, IPixel<TPixel>
     {
-        if (TestEnvironment.RunsOnCI && !TestEnvironment.IsWindows)
+        if (TestEnvironment.RunsOnCI)
         {
             return;
         }
@@ -457,12 +458,14 @@ public void Encode_AnimatedFormatTransform_FromGif<TPixel>(TestImageProvider<TPi
         image.Save(memStream, PngEncoder);
         memStream.Position = 0;
 
+        image.DebugSave(provider: provider, extension: "png", encoder: PngEncoder);
+
         using Image<TPixel> output = Image.Load<TPixel>(memStream);
 
         // TODO: Find a better way to compare.
-        // The image has been visually checked but the quantization pattern used in the png encoder
-        // means we cannot use an exact comparison nor replicate using the quantizing processor.
-        ImageComparer.TolerantPercentage(0.613f).VerifySimilarity(output, image);
+        // The image has been visually checked but the coarse cache used by the palette quantizer
+        // can lead to minor differences between frames.
+        ImageComparer.TolerantPercentage(percentage).VerifySimilarity(output, image);
 
         GifMetadata gif = image.Metadata.GetGifMetadata();
         PngMetadata png = output.Metadata.GetPngMetadata();
@@ -641,7 +644,7 @@ public void Issue2469_Quantized_Encode_Artifacts<TPixel>(TestImageProvider<TPixe
         encoded.CompareToReferenceOutput(ImageComparer.Exact, provider);
     }
 
-    // https://github.com/SixLabors/ImageSharp/issues/2469
+    // https://github.com/SixLabors/ImageSharp/issues/2668
     [Theory]
     [WithFile(TestImages.Png.Issue2668, PixelTypes.Rgba32)]
     public void Issue2668_Quantized_Encode_Alpha<TPixel>(TestImageProvider<TPixel> provider)
@@ -657,6 +660,35 @@ public void Issue2668_Quantized_Encode_Alpha<TPixel>(TestImageProvider<TPixel> p
         encoded.CompareToReferenceOutput(ImageComparer.Exact, provider);
     }
 
+    [Fact]
+    public void Issue_2862()
+    {
+        // Create a grayscale palette (or any other palette with colors that are very close to each other):
+        Rgba32[] palette = [.. Enumerable.Range(0, 256).Select(i => new Rgba32((byte)i, (byte)i, (byte)i))];
+
+        using Image<Rgba32> image = new(254, 4);
+        for (int y = 0; y < image.Height; y++)
+        {
+            for (int x = 0; x < image.Width; x++)
+            {
+                image[x, y] = palette[x];
+            }
+        }
+
+        using MemoryStream ms = new();
+        image.Save(ms, new PngEncoder
+        {
+            ColorType = PngColorType.Palette,
+            BitDepth = PngBitDepth.Bit8,
+            Quantizer = new PaletteQuantizer(palette.Select(Color.FromPixel).ToArray())
+        });
+
+        ms.Position = 0;
+
+        using Image<Rgba32> encoded = Image.Load<Rgba32>(ms);
+        ImageComparer.Exact.VerifySimilarity(image, encoded);
+    }
+
     private static void TestPngEncoderCore<TPixel>(
         TestImageProvider<TPixel> provider,
         PngColorType pngColorType,
diff --git a/tests/ImageSharp.Tests/Formats/WebP/WebpCommonUtilsTests.cs b/tests/ImageSharp.Tests/Formats/WebP/WebpCommonUtilsTests.cs
index a3fe028db5..1491cd13cf 100644
--- a/tests/ImageSharp.Tests/Formats/WebP/WebpCommonUtilsTests.cs
+++ b/tests/ImageSharp.Tests/Formats/WebP/WebpCommonUtilsTests.cs
@@ -106,7 +106,7 @@ private static void RunCheckNoneOpaqueWithNoneOpaquePixelsTest()
             174, 183, 189, 255,
             148, 158, 158, 255,
         };
-        Span<Bgra32> row = MemoryMarshal.Cast<byte, Bgra32>(rowBytes);
+        ReadOnlySpan<Bgra32> row = MemoryMarshal.Cast<byte, Bgra32>(rowBytes);
 
         bool noneOpaque;
         for (int length = 8; length < row.Length; length += 8)
@@ -188,7 +188,7 @@ private static void RunCheckNoneOpaqueWithOpaquePixelsTest()
             174, 183, 189, 255,
             148, 158, 158, 255,
         };
-        Span<Bgra32> row = MemoryMarshal.Cast<byte, Bgra32>(rowBytes);
+        ReadOnlySpan<Bgra32> row = MemoryMarshal.Cast<byte, Bgra32>(rowBytes);
 
         bool noneOpaque;
         for (int length = 8; length < row.Length; length += 8)
diff --git a/tests/ImageSharp.Tests/Formats/WebP/WebpDecoderTests.cs b/tests/ImageSharp.Tests/Formats/WebP/WebpDecoderTests.cs
index 657ab25546..adabb727d8 100644
--- a/tests/ImageSharp.Tests/Formats/WebP/WebpDecoderTests.cs
+++ b/tests/ImageSharp.Tests/Formats/WebP/WebpDecoderTests.cs
@@ -450,6 +450,22 @@ public void WebpDecoder_CanDecode_Issue2670<TPixel>(TestImageProvider<TPixel> pr
         image.CompareToOriginal(provider, ReferenceDecoder);
     }
 
+    // https://github.com/SixLabors/ImageSharp/issues/2866
+    [Theory]
+    [WithFile(Lossy.Issue2866, PixelTypes.Rgba32)]
+    public void WebpDecoder_CanDecode_Issue2866<TPixel>(TestImageProvider<TPixel> provider)
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        // Web
+        using Image<TPixel> image = provider.GetImage(
+            WebpDecoder.Instance,
+            new WebpDecoderOptions() { BackgroundColorHandling = BackgroundColorHandling.Ignore });
+
+        // We can't use the reference decoder here.
+        // It creates frames of different size without blending the frames.
+        image.DebugSave(provider, extension: "webp", encoder: new WebpEncoder());
+    }
+
     [Theory]
     [WithFile(Lossless.LossLessCorruptImage3, PixelTypes.Rgba32)]
     public void WebpDecoder_ThrowImageFormatException_OnInvalidImages<TPixel>(TestImageProvider<TPixel> provider)
diff --git a/tests/ImageSharp.Tests/Image/ImageFrameTests.cs b/tests/ImageSharp.Tests/Image/ImageFrameTests.cs
index e09ef487a8..58cf326001 100644
--- a/tests/ImageSharp.Tests/Image/ImageFrameTests.cs
+++ b/tests/ImageSharp.Tests/Image/ImageFrameTests.cs
@@ -119,7 +119,7 @@ public void CopyPixelDataTo_Success(bool disco, bool byteSpan)
             }
             else
             {
-                Span<La16> destination = MemoryMarshal.Cast<byte, La16>(actual);
+                Span<La16> destination = MemoryMarshal.Cast<byte, La16>(actual.AsSpan());
                 image.Frames.RootFrame.CopyPixelDataTo(destination);
             }
 
diff --git a/tests/ImageSharp.Tests/Image/ImageTests.cs b/tests/ImageSharp.Tests/Image/ImageTests.cs
index ac91ea948e..291e523816 100644
--- a/tests/ImageSharp.Tests/Image/ImageTests.cs
+++ b/tests/ImageSharp.Tests/Image/ImageTests.cs
@@ -197,7 +197,7 @@ public void CopyPixelDataTo_Success(bool disco, bool byteSpan)
             }
             else
             {
-                Span<La16> destination = MemoryMarshal.Cast<byte, La16>(actual);
+                Span<La16> destination = MemoryMarshal.Cast<byte, La16>(actual.AsSpan());
                 image.CopyPixelDataTo(destination);
             }
 
diff --git a/tests/ImageSharp.Tests/Quantization/WuQuantizerTests.cs b/tests/ImageSharp.Tests/Quantization/WuQuantizerTests.cs
index 74f2fc3b42..28a7c49e51 100644
--- a/tests/ImageSharp.Tests/Quantization/WuQuantizerTests.cs
+++ b/tests/ImageSharp.Tests/Quantization/WuQuantizerTests.cs
@@ -79,7 +79,7 @@ public void Palette256()
         }
 
         Configuration config = Configuration.Default;
-        WuQuantizer quantizer = new(new QuantizerOptions { Dither = null });
+        WuQuantizer quantizer = new(new QuantizerOptions { Dither = null, TransparencyThreshold = 0 });
 
         ImageFrame<Rgba32> frame = image.Frames.RootFrame;
 
@@ -152,7 +152,7 @@ private static void TestScale(Func<byte, Rgba32> pixelBuilder)
         }
 
         Configuration config = Configuration.Default;
-        WuQuantizer quantizer = new(new QuantizerOptions { Dither = null });
+        WuQuantizer quantizer = new(new QuantizerOptions { Dither = null, TransparencyThreshold = 0 });
 
         ImageFrame<Rgba32> frame = image.Frames.RootFrame;
         using (IQuantizer<Rgba32> frameQuantizer = quantizer.CreatePixelSpecificQuantizer<Rgba32>(config))
diff --git a/tests/ImageSharp.Tests/TestImages.cs b/tests/ImageSharp.Tests/TestImages.cs
index fafa1d2429..462d54154e 100644
--- a/tests/ImageSharp.Tests/TestImages.cs
+++ b/tests/ImageSharp.Tests/TestImages.cs
@@ -536,6 +536,7 @@ public static class Issues
             public const string Issue2450_B = "Gif/issues/issue_2450_2.gif";
             public const string Issue2198 = "Gif/issues/issue_2198.gif";
             public const string Issue2758 = "Gif/issues/issue_2758.gif";
+            public const string Issue2866 = "Gif/issues/issue_2866.gif";
             public const string Issue2859_A = "Gif/issues/issue_2859_A.gif";
             public const string Issue2859_B = "Gif/issues/issue_2859_B.gif";
         }
@@ -830,6 +831,7 @@ public static class Lossy
             public const string Issue2670 = "Webp/issues/Issue2670.webp";
             public const string Issue2763 = "Webp/issues/Issue2763.png";
             public const string Issue2801 = "Webp/issues/Issue2801.webp";
+            public const string Issue2866 = "Webp/issues/Issue2866.webp";
         }
     }
 
diff --git a/tests/ImageSharp.Tests/TestUtilities/ReferenceCodecs/MagickReferenceDecoder.cs b/tests/ImageSharp.Tests/TestUtilities/ReferenceCodecs/MagickReferenceDecoder.cs
index 74015a4eff..34c8170c3c 100644
--- a/tests/ImageSharp.Tests/TestUtilities/ReferenceCodecs/MagickReferenceDecoder.cs
+++ b/tests/ImageSharp.Tests/TestUtilities/ReferenceCodecs/MagickReferenceDecoder.cs
@@ -64,20 +64,27 @@ protected override Image<TPixel> Decode<TPixel>(DecoderOptions options, Stream s
         settings.SetDefines(pngReadDefines);
 
         using MagickImageCollection magickImageCollection = new(stream, settings);
+        int imageWidth = magickImageCollection.Max(x => x.Width);
+        int imageHeight = magickImageCollection.Max(x => x.Height);
+
         List<ImageFrame<TPixel>> framesList = [];
         foreach (IMagickImage<ushort> magicFrame in magickImageCollection)
         {
-            ImageFrame<TPixel> frame = new(configuration, (int)magicFrame.Width, (int)magicFrame.Height);
+            ImageFrame<TPixel> frame = new(configuration, imageWidth, imageHeight);
             framesList.Add(frame);
 
-            MemoryGroup<TPixel> framePixels = frame.PixelBuffer.FastMemoryGroup;
+            Buffer2DRegion<TPixel> buffer = frame.PixelBuffer.GetRegion(
+                imageWidth - magicFrame.Width,
+                imageHeight - magicFrame.Height,
+                magicFrame.Width,
+                magicFrame.Height);
 
             using IUnsafePixelCollection<ushort> pixels = magicFrame.GetPixelsUnsafe();
             if (magicFrame.Depth is 12 or 10 or 8 or 6 or 5 or 4 or 3 or 2 or 1)
             {
                 byte[] data = pixels.ToByteArray(PixelMapping.RGBA);
 
-                FromRgba32Bytes(configuration, data, framePixels);
+                FromRgba32Bytes(configuration, data, buffer);
             }
             else if (magicFrame.Depth is 16 or 14)
             {
@@ -88,7 +95,7 @@ protected override Image<TPixel> Decode<TPixel>(DecoderOptions options, Stream s
 
                 ushort[] data = pixels.ToShortArray(PixelMapping.RGBA);
                 Span<byte> bytes = MemoryMarshal.Cast<ushort, byte>(data.AsSpan());
-                FromRgba64Bytes(configuration, bytes, framePixels);
+                FromRgba64Bytes(configuration, bytes, buffer);
             }
             else
             {
@@ -111,33 +118,40 @@ protected override ImageInfo Identify(DecoderOptions options, Stream stream, Can
             PixelType = metadata.GetDecodedPixelTypeInfo()
         };
     }
-
-    private static void FromRgba32Bytes<TPixel>(Configuration configuration, Span<byte> rgbaBytes, IMemoryGroup<TPixel> destinationGroup)
+    private static void FromRgba32Bytes<TPixel>(
+        Configuration configuration,
+        Span<byte> rgbaBytes,
+        Buffer2DRegion<TPixel> destinationGroup)
         where TPixel : unmanaged, ImageSharp.PixelFormats.IPixel<TPixel>
     {
         Span<Rgba32> sourcePixels = MemoryMarshal.Cast<byte, Rgba32>(rgbaBytes);
-        foreach (Memory<TPixel> m in destinationGroup)
+        for (int y = 0; y < destinationGroup.Height; y++)
         {
-            Span<TPixel> destBuffer = m.Span;
+            Span<TPixel> destBuffer = destinationGroup.DangerousGetRowSpan(y);
             PixelOperations<TPixel>.Instance.FromRgba32(
                 configuration,
                 sourcePixels[..destBuffer.Length],
                 destBuffer);
+
             sourcePixels = sourcePixels[destBuffer.Length..];
         }
     }
 
-    private static void FromRgba64Bytes<TPixel>(Configuration configuration, Span<byte> rgbaBytes, IMemoryGroup<TPixel> destinationGroup)
+    private static void FromRgba64Bytes<TPixel>(
+        Configuration configuration,
+        Span<byte> rgbaBytes,
+        Buffer2DRegion<TPixel> destinationGroup)
         where TPixel : unmanaged, ImageSharp.PixelFormats.IPixel<TPixel>
     {
-        foreach (Memory<TPixel> m in destinationGroup)
+        for (int y = 0; y < destinationGroup.Height; y++)
         {
-            Span<TPixel> destBuffer = m.Span;
+            Span<TPixel> destBuffer = destinationGroup.DangerousGetRowSpan(y);
             PixelOperations<TPixel>.Instance.FromRgba64Bytes(
                 configuration,
                 rgbaBytes,
                 destBuffer,
                 destBuffer.Length);
+
             rgbaBytes = rgbaBytes[(destBuffer.Length * 8)..];
         }
     }
diff --git a/tests/Images/External/ReferenceOutput/BmpEncoderTests/Encode_8BitColor_WithOctreeQuantizer_rgb32.bmp b/tests/Images/External/ReferenceOutput/BmpEncoderTests/Encode_8BitColor_WithOctreeQuantizer_rgb32.bmp
index 2b8e05b070..291739dfa9 100644
--- a/tests/Images/External/ReferenceOutput/BmpEncoderTests/Encode_8BitColor_WithOctreeQuantizer_rgb32.bmp
+++ b/tests/Images/External/ReferenceOutput/BmpEncoderTests/Encode_8BitColor_WithOctreeQuantizer_rgb32.bmp
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:11375b15df083d98335f4a4baf0717e7fdd6b21ab2132a6815cadc787ac17e7d
+oid sha256:9d7441b03c24acb887b2d9a6e2346bb23e2d38293c3df3ff489d48593f87b29a
 size 9270
diff --git a/tests/Images/External/ReferenceOutput/BmpEncoderTests/Encode_8BitColor_WithWuQuantizer_rgb32.bmp b/tests/Images/External/ReferenceOutput/BmpEncoderTests/Encode_8BitColor_WithWuQuantizer_rgb32.bmp
index f7eb06c558..c69ed3130c 100644
--- a/tests/Images/External/ReferenceOutput/BmpEncoderTests/Encode_8BitColor_WithWuQuantizer_rgb32.bmp
+++ b/tests/Images/External/ReferenceOutput/BmpEncoderTests/Encode_8BitColor_WithWuQuantizer_rgb32.bmp
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:e063e97cd8a000de6830adcc3961a7dc41785d40cd4d83af10ca38d96e071362
+oid sha256:5d9f2745de2b6e7fc3b1403fe651f3bbba835c67a6fb410fc8a9d91a15b44328
 size 9270
diff --git a/tests/Images/External/ReferenceOutput/DitherTests/ApplyDiffusionFilterInBox_Rgba32_CalliphoraPartial.png b/tests/Images/External/ReferenceOutput/DitherTests/ApplyDiffusionFilterInBox_Rgba32_CalliphoraPartial.png
index de42d1bfc2..401ceaa36c 100644
--- a/tests/Images/External/ReferenceOutput/DitherTests/ApplyDiffusionFilterInBox_Rgba32_CalliphoraPartial.png
+++ b/tests/Images/External/ReferenceOutput/DitherTests/ApplyDiffusionFilterInBox_Rgba32_CalliphoraPartial.png
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:681b0e36298cb702683fb9ffb2a82f7dfd9080b268db19a03f413809f69d0e07
-size 273269
+oid sha256:596472e74050d968479b672c1d2436b179e41a7b99fcefb53286ad47e5a4fe13
+size 273115
diff --git a/tests/Images/External/ReferenceOutput/DitherTests/ApplyDitherFilterInBox_Rgba32_CalliphoraPartial.png b/tests/Images/External/ReferenceOutput/DitherTests/ApplyDitherFilterInBox_Rgba32_CalliphoraPartial.png
index 43e414da6d..35ed6dee46 100644
--- a/tests/Images/External/ReferenceOutput/DitherTests/ApplyDitherFilterInBox_Rgba32_CalliphoraPartial.png
+++ b/tests/Images/External/ReferenceOutput/DitherTests/ApplyDitherFilterInBox_Rgba32_CalliphoraPartial.png
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:a899a84c6af24bfad89f9fde75957c7a979d65bcf096ab667cb976efd71cb560
-size 271171
+oid sha256:a025a094c285cea8510430b0e3657bc59231b38132781e298d60a74238879912
+size 270699
diff --git a/tests/Images/External/ReferenceOutput/DitherTests/DiffusionFilter_WorksWithAllErrorDiffusers_Bike_Atkinson.png b/tests/Images/External/ReferenceOutput/DitherTests/DiffusionFilter_WorksWithAllErrorDiffusers_Bike_Atkinson.png
index 1656b2e9cb..0b03e4e185 100644
--- a/tests/Images/External/ReferenceOutput/DitherTests/DiffusionFilter_WorksWithAllErrorDiffusers_Bike_Atkinson.png
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index a3eefcba20..d8a04a055d 100644
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new file mode 100644
index 0000000000..0ead86bf89
--- /dev/null
+++ b/tests/Images/Input/Gif/issues/issue_2866.gif
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new file mode 100644
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new file mode 100644
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--- /dev/null
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From 19ea81575f8d4fe8d797646e13e256b125ee5351 Mon Sep 17 00:00:00 2001
From: James Jackson-South <james_south@hotmail.com>
Date: Wed, 26 Feb 2025 22:54:43 +1000
Subject: [PATCH 02/18] Use explicit ReadOnlySpan to fix CI build with preview
 lang

---
 src/ImageSharp/Formats/Png/PngEncoderCore.cs | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/ImageSharp/Formats/Png/PngEncoderCore.cs b/src/ImageSharp/Formats/Png/PngEncoderCore.cs
index 45d7d1270b..3f7f1e5623 100644
--- a/src/ImageSharp/Formats/Png/PngEncoderCore.cs
+++ b/src/ImageSharp/Formats/Png/PngEncoderCore.cs
@@ -1255,7 +1255,8 @@ private void EncodePixels<TPixel>(in Buffer2DRegion<TPixel> pixels, IndexedImage
         Span<byte> attempt = attemptBuffer.GetSpan();
         for (int y = 0; y < pixels.Height; y++)
         {
-            this.CollectAndFilterPixelRow(pixels.DangerousGetRowSpan(y), ref filter, ref attempt, quantized, y);
+            ReadOnlySpan<TPixel> rowSpan = pixels.DangerousGetRowSpan(y);
+            this.CollectAndFilterPixelRow(rowSpan, ref filter, ref attempt, quantized, y);
             deflateStream.Write(filter);
             this.SwapScanlineBuffers();
         }
@@ -1303,7 +1304,8 @@ private void EncodeAdam7Pixels<TPixel>(in Buffer2DRegion<TPixel> pixels, ZlibDef
                 // Encode data
                 // Note: quantized parameter not used
                 // Note: row parameter not used
-                this.CollectAndFilterPixelRow(block, ref filter, ref attempt, null, -1);
+                ReadOnlySpan<TPixel> blockSpan = block;
+                this.CollectAndFilterPixelRow(blockSpan, ref filter, ref attempt, null, -1);
                 deflateStream.Write(filter);
 
                 this.SwapScanlineBuffers();

From e73349562822cb57d5c7fbc64b767d25aad4b08f Mon Sep 17 00:00:00 2001
From: James Jackson-South <james_south@hotmail.com>
Date: Wed, 26 Feb 2025 23:03:45 +1000
Subject: [PATCH 03/18] remove old unused type

---
 .../Quantization/OctreeQuantizer{TPixel}.cs   | 475 ------------------
 1 file changed, 475 deletions(-)

diff --git a/src/ImageSharp/Processing/Processors/Quantization/OctreeQuantizer{TPixel}.cs b/src/ImageSharp/Processing/Processors/Quantization/OctreeQuantizer{TPixel}.cs
index be00bc433a..65e814e620 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/OctreeQuantizer{TPixel}.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/OctreeQuantizer{TPixel}.cs
@@ -654,479 +654,4 @@ public static int GetColorIndex(Rgba32 color, int level)
             }
         }
     }
-
-    /// <summary>
-    /// Class which does the actual quantization.
-    /// </summary>
-    private sealed class Octree2
-    {
-        /// <summary>
-        /// The root of the Octree2
-        /// </summary>
-        private readonly OctreeNode root;
-
-        /// <summary>
-        /// Maximum number of significant bits in the image
-        /// </summary>
-        private readonly int maxColorBits;
-
-        /// <summary>
-        /// The threshold for transparent colors.
-        /// </summary>
-        private readonly int transparencyThreshold;
-
-        /// <summary>
-        /// Store the last node quantized
-        /// </summary>
-        private OctreeNode? previousNode;
-
-        /// <summary>
-        /// Cache the previous color quantized
-        /// </summary>
-        private Rgba32 previousColor;
-
-        /// <summary>
-        /// Initializes a new instance of the <see cref="Octree2"/> class.
-        /// </summary>
-        /// <param name="maxColorBits">
-        /// The maximum number of significant bits in the image
-        /// </param>
-        /// <param name="transparencyThreshold">The threshold for transparent colors.</param>
-        public Octree2(int maxColorBits, int transparencyThreshold)
-        {
-            this.maxColorBits = maxColorBits;
-            this.transparencyThreshold = transparencyThreshold;
-            this.Leaves = 0;
-            this.ReducibleNodes = new OctreeNode[9];
-            this.root = new OctreeNode(0, this.maxColorBits, this);
-            this.previousColor = default;
-            this.previousNode = null;
-        }
-
-        /// <summary>
-        /// Gets or sets the number of leaves in the tree
-        /// </summary>
-        public int Leaves
-        {
-            [MethodImpl(InliningOptions.ShortMethod)]
-            get;
-
-            [MethodImpl(InliningOptions.ShortMethod)]
-            set;
-        }
-
-        /// <summary>
-        /// Gets the array of reducible nodes
-        /// </summary>
-        private OctreeNode?[] ReducibleNodes
-        {
-            [MethodImpl(InliningOptions.ShortMethod)]
-            get;
-        }
-
-        /// <summary>
-        /// Add a given color value to the Octree2
-        /// </summary>
-        /// <param name="color">The color to add.</param>
-        public void AddColor(Rgba32 color)
-        {
-            if (color.A < this.transparencyThreshold)
-            {
-                color.A = 0;
-            }
-
-            // Check if this request is for the same color as the last
-            if (this.previousColor.Equals(color))
-            {
-                // If so, check if I have a previous node setup.
-                if (this.previousNode is null)
-                {
-                    this.previousColor = color;
-                    this.root.AddColor(color, this.maxColorBits, 0, this);
-                }
-                else
-                {
-                    // Just update the previous node
-                    this.previousNode.Increment(color, this);
-                }
-            }
-            else
-            {
-                this.previousColor = color;
-                this.root.AddColor(color, this.maxColorBits, 0, this);
-            }
-        }
-
-        /// <summary>
-        /// Convert the nodes in the Octree2 to a palette with a maximum of colorCount colors
-        /// </summary>
-        /// <param name="palette">The palette to fill.</param>
-        /// <param name="colorCount">The maximum number of colors</param>
-        /// <param name="paletteIndex">The palette index, used to calculate the final size of the palette.</param>
-        [MethodImpl(InliningOptions.ShortMethod)]
-        public void Palettize(Span<TPixel> palette, int colorCount, ref int paletteIndex)
-        {
-            while (this.Leaves > colorCount)
-            {
-                this.Reduce();
-            }
-
-            this.root.ConstructPalette(palette, ref paletteIndex);
-        }
-
-        /// <summary>
-        /// Get the palette index for the passed color
-        /// </summary>
-        /// <param name="color">The color to match.</param>
-        /// <returns>
-        /// The <see cref="int"/> index.
-        /// </returns>
-        [MethodImpl(InliningOptions.ShortMethod)]
-        public int GetPaletteIndex(TPixel color)
-            => this.root.GetPaletteIndex(color.ToRgba32(), 0);
-
-        /// <summary>
-        /// Keep track of the previous node that was quantized
-        /// </summary>
-        /// <param name="node">
-        /// The node last quantized
-        /// </param>
-        [MethodImpl(InliningOptions.ShortMethod)]
-        public void TrackPrevious(OctreeNode node) => this.previousNode = node;
-
-        /// <summary>
-        /// Reduce the depth of the tree
-        /// </summary>
-        private void Reduce()
-        {
-            // Find the deepest level containing at least one reducible node
-            int index = this.maxColorBits - 1;
-            while ((index > 0) && (this.ReducibleNodes[index] is null))
-            {
-                index--;
-            }
-
-            // Reduce the node most recently added to the list at level 'index'
-            OctreeNode node = this.ReducibleNodes[index]!;
-            this.ReducibleNodes[index] = node.NextReducible;
-
-            // Decrement the leaf count after reducing the node
-            this.Leaves -= node.Reduce(this);
-
-            // And just in case I've reduced the last color to be added, and the next color to
-            // be added is the same, invalidate the previousNode...
-            this.previousNode = null;
-        }
-
-        /// <summary>
-        /// Class which encapsulates each node in the tree
-        /// </summary>
-        public sealed class OctreeNode
-        {
-            /// <summary>
-            /// Pointers to any child nodes
-            /// </summary>
-            private readonly OctreeNode?[]? children;
-
-            /// <summary>
-            /// Flag indicating that this is a leaf node
-            /// </summary>
-            private bool leaf;
-
-            /// <summary>
-            /// Number of pixels in this node
-            /// </summary>
-            private int pixelCount;
-
-            /// <summary>
-            /// Red component
-            /// </summary>
-            private int red;
-
-            /// <summary>
-            /// Green Component
-            /// </summary>
-            private int green;
-
-            /// <summary>
-            /// Blue component
-            /// </summary>
-            private int blue;
-
-            /// <summary>
-            /// Alpha component
-            /// </summary>
-            private int alpha;
-
-            /// <summary>
-            /// The index of this node in the palette
-            /// </summary>
-            private int paletteIndex;
-
-            /// <summary>
-            /// Initializes a new instance of the <see cref="OctreeNode"/> class.
-            /// </summary>
-            /// <param name="level">The level in the tree = 0 - 7.</param>
-            /// <param name="colorBits">The number of significant color bits in the image.</param>
-            /// <param name="octree">The tree to which this node belongs.</param>
-            public OctreeNode(int level, int colorBits, Octree2 octree)
-            {
-                // Construct the new node
-                this.leaf = level == colorBits;
-
-                this.red = this.green = this.blue = this.alpha = 0;
-                this.pixelCount = 0;
-
-                // If a leaf, increment the leaf count
-                if (this.leaf)
-                {
-                    octree.Leaves++;
-                    this.NextReducible = null;
-                    this.children = null;
-                }
-                else
-                {
-                    // Otherwise add this to the reducible nodes
-                    this.NextReducible = octree.ReducibleNodes[level];
-                    octree.ReducibleNodes[level] = this;
-                    this.children = new OctreeNode[16];
-                }
-            }
-
-            /// <summary>
-            /// Gets the next reducible node
-            /// </summary>
-            public OctreeNode? NextReducible
-            {
-                [MethodImpl(InliningOptions.ShortMethod)]
-                get;
-            }
-
-            /// <summary>
-            /// Add a color into the tree
-            /// </summary>
-            /// <param name="color">The color to add.</param>
-            /// <param name="colorBits">The number of significant color bits.</param>
-            /// <param name="level">The level in the tree.</param>
-            /// <param name="octree">The tree to which this node belongs.</param>
-            public void AddColor(Rgba32 color, int colorBits, int level, Octree2 octree)
-            {
-                // Update the color information if this is a leaf
-                if (this.leaf)
-                {
-                    this.Increment(color, octree);
-
-                    // Setup the previous node
-                    octree.TrackPrevious(this);
-                }
-                else
-                {
-                    // Go to the next level down in the tree
-                    int index = GetColorIndex(color, level);
-
-                    OctreeNode? child = this.children![index];
-                    if (child is null)
-                    {
-                        // Create a new child node and store it in the array
-                        child = new OctreeNode(level + 1, colorBits, octree);
-                        this.children[index] = child;
-                    }
-
-                    // Add the color to the child node
-                    child.AddColor(color, colorBits, level + 1, octree);
-                }
-            }
-
-            /// <summary>
-            /// Reduce this node by removing all of its children.
-            /// </summary>
-            /// <returns>The number of leaves removed</returns>
-            /// <param name="octree">The tree to which this node belongs.</param>
-            public int Reduce(Octree2 octree)
-            {
-                if (this.leaf)
-                {
-                    return 1;
-                }
-
-                int childNodes = 0;
-                int sumRed = 0, sumGreen = 0, sumBlue = 0, sumAlpha = 0, pixelCount = 0;
-
-                // Loop through all children.
-                for (int index = 0; index < this.children!.Length; index++)
-                {
-                    OctreeNode? child = this.children[index];
-                    if (child != null)
-                    {
-                        childNodes++;
-
-                        sumRed += child.red;
-                        sumGreen += child.green;
-                        sumBlue += child.blue;
-                        sumAlpha += child.alpha;
-                        pixelCount += child.pixelCount;
-
-                        // Remove the child reference.
-                        this.children[index] = null;
-                    }
-                }
-
-                if (pixelCount > 0)
-                {
-                    int offset = pixelCount >> 1;
-                    this.red = sumRed;
-                    this.green = sumGreen;
-                    this.blue = sumBlue;
-                    this.alpha = ((sumAlpha + offset) / pixelCount < octree.transparencyThreshold) ? 0 : sumAlpha;
-                    this.pixelCount = pixelCount;
-                }
-                else
-                {
-                    this.red = this.green = this.blue = this.alpha = 0;
-                    this.pixelCount = 0;
-                }
-
-                // Convert this node into a leaf.
-                this.leaf = true;
-
-                // Return the number of nodes merged (for decrementing the leaf count).
-                return childNodes - 1;
-            }
-
-            /// <summary>
-            /// Traverse the tree, building up the color palette
-            /// </summary>
-            /// <param name="palette">The palette</param>
-            /// <param name="index">The current palette index</param>
-            [MethodImpl(InliningOptions.ColdPath)]
-            public void ConstructPalette(Span<TPixel> palette, ref int index)
-            {
-                if (this.leaf)
-                {
-                    // Set the color of the palette entry
-                    Vector4 sum = new(this.red, this.green, this.blue, this.alpha);
-                    Vector4 offset = new(this.pixelCount >> 1);
-
-                    Vector4 vector = Vector4.Clamp(
-                        (sum + offset) / this.pixelCount,
-                        Vector4.Zero,
-                        new Vector4(255));
-
-                    palette[index] = TPixel.FromRgba32(new Rgba32((byte)vector.X, (byte)vector.Y, (byte)vector.Z, (byte)vector.W));
-
-                    // Consume the next palette index
-                    this.paletteIndex = index++;
-                }
-                else
-                {
-                    // Loop through children looking for leaves
-                    for (int i = 0; i < this.children!.Length; i++)
-                    {
-                        this.children[i]?.ConstructPalette(palette, ref index);
-                    }
-                }
-            }
-
-            /// <summary>
-            /// Return the palette index for the passed color
-            /// </summary>
-            /// <param name="pixel">The pixel data.</param>
-            /// <param name="level">The level.</param>
-            /// <returns>
-            /// The <see cref="int"/> representing the index of the pixel in the palette.
-            /// </returns>
-            [MethodImpl(InliningOptions.ColdPath)]
-            public int GetPaletteIndex(Rgba32 pixel, int level)
-            {
-                if (this.leaf)
-                {
-                    return this.paletteIndex;
-                }
-
-                int colorIndex = GetColorIndex(pixel, level);
-                OctreeNode? child = this.children![colorIndex];
-
-                int index = -1;
-                if (child != null)
-                {
-                    index = child.GetPaletteIndex(pixel, level + 1);
-                }
-                else
-                {
-                    // Check other children.
-                    for (int i = 0; i < this.children.Length; i++)
-                    {
-                        child = this.children[i];
-                        if (child != null)
-                        {
-                            int childIndex = child.GetPaletteIndex(pixel, level + 1);
-                            if (childIndex != -1)
-                            {
-                                return childIndex;
-                            }
-                        }
-                    }
-                }
-
-                return index;
-            }
-
-            /// <summary>
-            /// Gets the color index at the given level.
-            /// </summary>
-            /// <param name="color">The color.</param>
-            /// <param name="level">The node level.</param>
-            /// <returns>The <see cref="int"/> index.</returns>
-            [MethodImpl(InliningOptions.ShortMethod)]
-            private static int GetColorIndex(Rgba32 color, int level)
-            {
-                int shift = 7 - level;
-                byte mask = (byte)(1 << shift);
-
-                // Compute luminance of the RGB channels.
-                int luminance = ColorNumerics.Get8BitBT709Luminance(color.R, color.G, color.B);
-
-                // Shift the threshold (arbitrary) right by the current level.
-                // This allows us to partition the RGB space into smaller and smaller cubes
-                // with increasing accuracy for the alpha component.
-                int darkThreshold = 24 >> level;
-
-                // For fully opaque and bright pixels, ignore the alpha bit to achieve finer RGB partitioning.
-                // For dark pixels, include the alpha bit so that dark drop shadows remain distinct.
-                if (color.A == 255 && luminance > darkThreshold)
-                {
-                    int rBits = ((color.R & mask) >> shift) << 2;
-                    int gBits = ((color.G & mask) >> shift) << 1;
-                    int bBits = (color.B & mask) >> shift;
-                    return rBits | gBits | bBits;
-                }
-                else
-                {
-                    int aBits = ((color.A & mask) >> shift) << 3;
-                    int rBits = ((color.R & mask) >> shift) << 2;
-                    int gBits = ((color.G & mask) >> shift) << 1;
-                    int bBits = (color.B & mask) >> shift;
-                    return aBits | rBits | gBits | bBits;
-                }
-            }
-
-            /// <summary>
-            /// Increment the color count and add to the color information
-            /// </summary>
-            /// <param name="color">The pixel to add.</param>
-            /// <param name="octree">The parent octree.</param>
-            [MethodImpl(InliningOptions.ShortMethod)]
-            public void Increment(Rgba32 color, Octree2 octree)
-            {
-                this.pixelCount++;
-                this.red += color.R;
-                this.green += color.G;
-                this.blue += color.B;
-
-                int sumAlpha = this.alpha + color.A;
-                int offset = this.pixelCount >> 1;
-                this.alpha = ((sumAlpha + offset) / this.pixelCount < octree.transparencyThreshold) ? 0 : sumAlpha;
-            }
-        }
-    }
 }

From 05c552524b1862c4b64c40ab14c8e7001932c1de Mon Sep 17 00:00:00 2001
From: James Jackson-South <james_south@hotmail.com>
Date: Thu, 27 Feb 2025 20:48:31 +1000
Subject: [PATCH 04/18] Threshold on the way out also.

---
 .../Quantization/WuQuantizer{TPixel}.cs       | 20 +++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/src/ImageSharp/Processing/Processors/Quantization/WuQuantizer{TPixel}.cs b/src/ImageSharp/Processing/Processors/Quantization/WuQuantizer{TPixel}.cs
index e637c2cf04..db6490259f 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/WuQuantizer{TPixel}.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/WuQuantizer{TPixel}.cs
@@ -74,7 +74,8 @@ internal struct WuQuantizer<TPixel> : IQuantizer<TPixel>
     private readonly IMemoryOwner<TPixel> paletteOwner;
     private ReadOnlyMemory<TPixel> palette;
     private int maxColors;
-    private short transparencyThreshold;
+    private readonly float transparencyThreshold;
+    private readonly short transparencyThreshold255;
     private readonly Box[] colorCube;
     private EuclideanPixelMap<TPixel>? pixelMap;
     private readonly bool isDithering;
@@ -102,8 +103,9 @@ public WuQuantizer(Configuration configuration, QuantizerOptions options)
         this.isDisposed = false;
         this.pixelMap = default;
         this.palette = default;
-        this.isDithering = this.isDithering = this.Options.Dither is not null;
-        this.transparencyThreshold = (short)(this.Options.TransparencyThreshold * 255);
+        this.isDithering = this.Options.Dither is not null;
+        this.transparencyThreshold = this.Options.TransparencyThreshold;
+        this.transparencyThreshold255 = (short)(this.Options.TransparencyThreshold * 255);
     }
 
     /// <inheritdoc/>
@@ -152,7 +154,13 @@ private void ResolvePalette()
             Moment moment = Volume(ref this.colorCube[k], momentsSpan);
             if (moment.Weight > 0)
             {
-                paletteSpan[k] = TPixel.FromScaledVector4(moment.Normalize());
+                Vector4 normalized = moment.Normalize();
+                if (normalized.W < this.transparencyThreshold)
+                {
+                    normalized = Vector4.Zero;
+                }
+
+                paletteSpan[k] = TPixel.FromScaledVector4(normalized);
             }
         }
 
@@ -179,11 +187,11 @@ public readonly byte GetQuantizedColor(TPixel color, out TPixel match)
         // In this case, we must use the pixel map to get the closest color.
         if (this.isDithering)
         {
-            return (byte)this.pixelMap!.GetClosestColor(color, out match, this.transparencyThreshold);
+            return (byte)this.pixelMap!.GetClosestColor(color, out match, this.transparencyThreshold255);
         }
 
         Rgba32 rgba = color.ToRgba32();
-        if (rgba.A < this.transparencyThreshold)
+        if (rgba.A < this.transparencyThreshold255)
         {
             rgba = default;
         }

From c573228b0900ea160103e5383a9bdd2802de3323 Mon Sep 17 00:00:00 2001
From: James Jackson-South <james_south@hotmail.com>
Date: Mon, 17 Mar 2025 16:52:45 +1000
Subject: [PATCH 05/18] Upstream fixes.

---
 .../Formats/Cur/CurFrameMetadata.cs           |   2 -
 src/ImageSharp/Formats/Cur/CurMetadata.cs     |   6 +-
 .../Formats/FormatConnectingFrameMetadata.cs  |   5 -
 .../Formats/FormatConnectingMetadata.cs       |   5 -
 src/ImageSharp/Formats/Gif/GifDecoderCore.cs  | 101 +++++++++++++-----
 .../Formats/Gif/GifFrameMetadata.cs           |  26 +----
 src/ImageSharp/Formats/Gif/GifMetadata.cs     |  37 +------
 .../Formats/Ico/IcoFrameMetadata.cs           |   4 +-
 src/ImageSharp/Formats/Ico/IcoMetadata.cs     |   6 +-
 .../Formats/Icon/IconEncoderCore.cs           |  16 ++-
 src/ImageSharp/Formats/Png/PngEncoderCore.cs  |   3 +-
 src/ImageSharp/Formats/Png/PngMetadata.cs     |  21 ----
 .../Formats/Webp/Lossy/Vp8Decoder.cs          |  10 +-
 .../Quantization/EuclideanPixelMap{TPixel}.cs |  10 +-
 .../Formats/Gif/GifDecoderTests.cs            |  35 ++++++
 .../Formats/Gif/GifEncoderTests.cs            |  12 ++-
 .../Formats/Icon/Cur/CurEncoderTests.cs       |   5 +-
 .../Formats/Png/PngEncoderTests.cs            |  32 +++---
 .../Formats/WebP/WebpEncoderTests.cs          |  59 ++++++++++
 tests/ImageSharp.Tests/TestImages.cs          |  30 ++++++
 .../TestUtilities/TestImageExtensions.cs      |  91 ++++++++++++++++
 .../00.png                                    |   3 +
 .../01.png                                    |   3 +
 .../02.png                                    |   3 +
 .../03.png                                    |   3 +
 .../00.png                                    |   3 +
 .../01.png                                    |   3 +
 .../02.png                                    |   3 +
 .../03.png                                    |   3 +
 .../00.png                                    |   3 +
 .../01.png                                    |   3 +
 .../02.png                                    |   3 +
 .../03.png                                    |   3 +
 .../00.png                                    |   3 +
 .../01.png                                    |   3 +
 .../02.png                                    |   3 +
 .../03.png                                    |   3 +
 .../00.png                                    |   3 +
 .../01.png                                    |   3 +
 .../02.png                                    |   3 +
 .../03.png                                    |   3 +
 .../00.png                                    |   3 +
 .../01.png                                    |   3 +
 .../02.png                                    |   3 +
 .../03.png                                    |   3 +
 ...Animation_Rgba32_static_nontransparent.png |   3 +
 ...No_Animation_Rgba32_static_transparent.png |   3 +
 ...2012BadMinCode_Rgba32_issue2012_drona1.png |   4 +-
 .../00.png                                    |   4 +-
 .../01.png                                    |   4 +-
 .../02.png                                    |   4 +-
 .../03.png                                    |   4 +-
 .../04.png                                    |   4 +-
 .../05.png                                    |   4 +-
 .../06.png                                    |   4 +-
 .../07.png                                    |   4 +-
 .../00.gif                                    |   3 +
 .../08.gif                                    |   3 +
 .../104.gif                                   |   3 +
 .../112.gif                                   |   3 +
 .../16.gif                                    |   3 +
 .../24.gif                                    |   3 +
 .../32.gif                                    |   3 +
 .../40.gif                                    |   3 +
 .../48.gif                                    |   3 +
 .../56.gif                                    |   3 +
 .../64.gif                                    |   3 +
 .../72.gif                                    |   3 +
 .../80.gif                                    |   3 +
 .../88.gif                                    |   3 +
 .../96.gif                                    |   3 +
 .../00.png                                    |   3 +
 .../08.png                                    |   3 +
 .../104.png                                   |   3 +
 .../112.png                                   |   3 +
 .../16.png                                    |   3 +
 .../24.png                                    |   3 +
 .../32.png                                    |   3 +
 .../40.png                                    |   3 +
 .../48.png                                    |   3 +
 .../56.png                                    |   3 +
 .../64.png                                    |   3 +
 .../72.png                                    |   3 +
 .../80.png                                    |   3 +
 .../88.png                                    |   3 +
 .../96.png                                    |   3 +
 .../00.png                                    |   3 +
 .../08.png                                    |   3 +
 tests/Images/Input/Gif/animated_loop.gif      |   3 +
 .../Input/Gif/animated_loop_interlaced.gif    |   3 +
 ...transparent_firstframerestoreprev_loop.gif |   3 +
 ...mated_transparent_frame_norestore_loop.gif |   3 +
 ...ansparent_frame_restorebackground_loop.gif |   3 +
 ...ted_transparent_frame_restoreprev_loop.gif |   3 +
 .../Input/Gif/animated_transparent_loop.gif   |   3 +
 .../animated_transparent_restoreprev_loop.gif |   3 +
 .../Input/Gif/static_nontransparent.gif       |   3 +
 tests/Images/Input/Gif/static_transparent.gif |   3 +
 tests/Images/Input/Webp/alpha-blend-2.webp    |   3 +
 tests/Images/Input/Webp/alpha-blend-3.webp    |   3 +
 tests/Images/Input/Webp/alpha-blend-4.webp    |   3 +
 tests/Images/Input/Webp/alpha-blend.webp      |   3 +
 102 files changed, 587 insertions(+), 181 deletions(-)
 create mode 100644 tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Animated_Rgba32_animated_loop.gif/00.png
 create mode 100644 tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Animated_Rgba32_animated_loop.gif/01.png
 create mode 100644 tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Animated_Rgba32_animated_loop.gif/02.png
 create mode 100644 tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Animated_Rgba32_animated_loop.gif/03.png
 create mode 100644 tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Animated_Rgba32_animated_loop_interlaced.gif/00.png
 create mode 100644 tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Animated_Rgba32_animated_loop_interlaced.gif/01.png
 create mode 100644 tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Animated_Rgba32_animated_loop_interlaced.gif/02.png
 create mode 100644 tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Animated_Rgba32_animated_loop_interlaced.gif/03.png
 create mode 100644 tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Animated_WithTransparency_Rgba32_animated_transparent_firstframerestoreprev_loop.gif/00.png
 create mode 100644 tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Animated_WithTransparency_Rgba32_animated_transparent_firstframerestoreprev_loop.gif/01.png
 create mode 100644 tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Animated_WithTransparency_Rgba32_animated_transparent_firstframerestoreprev_loop.gif/02.png
 create mode 100644 tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Animated_WithTransparency_Rgba32_animated_transparent_firstframerestoreprev_loop.gif/03.png
 create mode 100644 tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Animated_WithTransparency_Rgba32_animated_transparent_frame_norestore_loop.gif/00.png
 create mode 100644 tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Animated_WithTransparency_Rgba32_animated_transparent_frame_norestore_loop.gif/01.png
 create mode 100644 tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Animated_WithTransparency_Rgba32_animated_transparent_frame_norestore_loop.gif/02.png
 create mode 100644 tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Animated_WithTransparency_Rgba32_animated_transparent_frame_norestore_loop.gif/03.png
 create mode 100644 tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Animated_WithTransparency_Rgba32_animated_transparent_frame_restoreprev_loop.gif/00.png
 create mode 100644 tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Animated_WithTransparency_Rgba32_animated_transparent_frame_restoreprev_loop.gif/01.png
 create mode 100644 tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Animated_WithTransparency_Rgba32_animated_transparent_frame_restoreprev_loop.gif/02.png
 create mode 100644 tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Animated_WithTransparency_Rgba32_animated_transparent_frame_restoreprev_loop.gif/03.png
 create mode 100644 tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Animated_WithTransparency_Rgba32_animated_transparent_loop.gif/00.png
 create mode 100644 tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Animated_WithTransparency_Rgba32_animated_transparent_loop.gif/01.png
 create mode 100644 tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Animated_WithTransparency_Rgba32_animated_transparent_loop.gif/02.png
 create mode 100644 tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Animated_WithTransparency_Rgba32_animated_transparent_loop.gif/03.png
 create mode 100644 tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Static_No_Animation_Rgba32_static_nontransparent.png
 create mode 100644 tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Static_No_Animation_Rgba32_static_transparent.png
 create mode 100644 tests/Images/External/ReferenceOutput/GifEncoderTests/GifEncoder_CanDecode_AndEncode_Issue2866_Rgba32_issue_2866.gif/00.gif
 create mode 100644 tests/Images/External/ReferenceOutput/GifEncoderTests/GifEncoder_CanDecode_AndEncode_Issue2866_Rgba32_issue_2866.gif/08.gif
 create mode 100644 tests/Images/External/ReferenceOutput/GifEncoderTests/GifEncoder_CanDecode_AndEncode_Issue2866_Rgba32_issue_2866.gif/104.gif
 create mode 100644 tests/Images/External/ReferenceOutput/GifEncoderTests/GifEncoder_CanDecode_AndEncode_Issue2866_Rgba32_issue_2866.gif/112.gif
 create mode 100644 tests/Images/External/ReferenceOutput/GifEncoderTests/GifEncoder_CanDecode_AndEncode_Issue2866_Rgba32_issue_2866.gif/16.gif
 create mode 100644 tests/Images/External/ReferenceOutput/GifEncoderTests/GifEncoder_CanDecode_AndEncode_Issue2866_Rgba32_issue_2866.gif/24.gif
 create mode 100644 tests/Images/External/ReferenceOutput/GifEncoderTests/GifEncoder_CanDecode_AndEncode_Issue2866_Rgba32_issue_2866.gif/32.gif
 create mode 100644 tests/Images/External/ReferenceOutput/GifEncoderTests/GifEncoder_CanDecode_AndEncode_Issue2866_Rgba32_issue_2866.gif/40.gif
 create mode 100644 tests/Images/External/ReferenceOutput/GifEncoderTests/GifEncoder_CanDecode_AndEncode_Issue2866_Rgba32_issue_2866.gif/48.gif
 create mode 100644 tests/Images/External/ReferenceOutput/GifEncoderTests/GifEncoder_CanDecode_AndEncode_Issue2866_Rgba32_issue_2866.gif/56.gif
 create mode 100644 tests/Images/External/ReferenceOutput/GifEncoderTests/GifEncoder_CanDecode_AndEncode_Issue2866_Rgba32_issue_2866.gif/64.gif
 create mode 100644 tests/Images/External/ReferenceOutput/GifEncoderTests/GifEncoder_CanDecode_AndEncode_Issue2866_Rgba32_issue_2866.gif/72.gif
 create mode 100644 tests/Images/External/ReferenceOutput/GifEncoderTests/GifEncoder_CanDecode_AndEncode_Issue2866_Rgba32_issue_2866.gif/80.gif
 create mode 100644 tests/Images/External/ReferenceOutput/GifEncoderTests/GifEncoder_CanDecode_AndEncode_Issue2866_Rgba32_issue_2866.gif/88.gif
 create mode 100644 tests/Images/External/ReferenceOutput/GifEncoderTests/GifEncoder_CanDecode_AndEncode_Issue2866_Rgba32_issue_2866.gif/96.gif
 create mode 100644 tests/Images/External/ReferenceOutput/PngEncoderTests/Encode_AnimatedFormatTransform_FromGif_Rgba32_issue_2866.gif/00.png
 create mode 100644 tests/Images/External/ReferenceOutput/PngEncoderTests/Encode_AnimatedFormatTransform_FromGif_Rgba32_issue_2866.gif/08.png
 create mode 100644 tests/Images/External/ReferenceOutput/PngEncoderTests/Encode_AnimatedFormatTransform_FromGif_Rgba32_issue_2866.gif/104.png
 create mode 100644 tests/Images/External/ReferenceOutput/PngEncoderTests/Encode_AnimatedFormatTransform_FromGif_Rgba32_issue_2866.gif/112.png
 create mode 100644 tests/Images/External/ReferenceOutput/PngEncoderTests/Encode_AnimatedFormatTransform_FromGif_Rgba32_issue_2866.gif/16.png
 create mode 100644 tests/Images/External/ReferenceOutput/PngEncoderTests/Encode_AnimatedFormatTransform_FromGif_Rgba32_issue_2866.gif/24.png
 create mode 100644 tests/Images/External/ReferenceOutput/PngEncoderTests/Encode_AnimatedFormatTransform_FromGif_Rgba32_issue_2866.gif/32.png
 create mode 100644 tests/Images/External/ReferenceOutput/PngEncoderTests/Encode_AnimatedFormatTransform_FromGif_Rgba32_issue_2866.gif/40.png
 create mode 100644 tests/Images/External/ReferenceOutput/PngEncoderTests/Encode_AnimatedFormatTransform_FromGif_Rgba32_issue_2866.gif/48.png
 create mode 100644 tests/Images/External/ReferenceOutput/PngEncoderTests/Encode_AnimatedFormatTransform_FromGif_Rgba32_issue_2866.gif/56.png
 create mode 100644 tests/Images/External/ReferenceOutput/PngEncoderTests/Encode_AnimatedFormatTransform_FromGif_Rgba32_issue_2866.gif/64.png
 create mode 100644 tests/Images/External/ReferenceOutput/PngEncoderTests/Encode_AnimatedFormatTransform_FromGif_Rgba32_issue_2866.gif/72.png
 create mode 100644 tests/Images/External/ReferenceOutput/PngEncoderTests/Encode_AnimatedFormatTransform_FromGif_Rgba32_issue_2866.gif/80.png
 create mode 100644 tests/Images/External/ReferenceOutput/PngEncoderTests/Encode_AnimatedFormatTransform_FromGif_Rgba32_issue_2866.gif/88.png
 create mode 100644 tests/Images/External/ReferenceOutput/PngEncoderTests/Encode_AnimatedFormatTransform_FromGif_Rgba32_issue_2866.gif/96.png
 create mode 100644 tests/Images/External/ReferenceOutput/PngEncoderTests/Encode_AnimatedFormatTransform_FromGif_Rgba32_leo.gif/00.png
 create mode 100644 tests/Images/External/ReferenceOutput/PngEncoderTests/Encode_AnimatedFormatTransform_FromGif_Rgba32_leo.gif/08.png
 create mode 100644 tests/Images/Input/Gif/animated_loop.gif
 create mode 100644 tests/Images/Input/Gif/animated_loop_interlaced.gif
 create mode 100644 tests/Images/Input/Gif/animated_transparent_firstframerestoreprev_loop.gif
 create mode 100644 tests/Images/Input/Gif/animated_transparent_frame_norestore_loop.gif
 create mode 100644 tests/Images/Input/Gif/animated_transparent_frame_restorebackground_loop.gif
 create mode 100644 tests/Images/Input/Gif/animated_transparent_frame_restoreprev_loop.gif
 create mode 100644 tests/Images/Input/Gif/animated_transparent_loop.gif
 create mode 100644 tests/Images/Input/Gif/animated_transparent_restoreprev_loop.gif
 create mode 100644 tests/Images/Input/Gif/static_nontransparent.gif
 create mode 100644 tests/Images/Input/Gif/static_transparent.gif
 create mode 100644 tests/Images/Input/Webp/alpha-blend-2.webp
 create mode 100644 tests/Images/Input/Webp/alpha-blend-3.webp
 create mode 100644 tests/Images/Input/Webp/alpha-blend-4.webp
 create mode 100644 tests/Images/Input/Webp/alpha-blend.webp

diff --git a/src/ImageSharp/Formats/Cur/CurFrameMetadata.cs b/src/ImageSharp/Formats/Cur/CurFrameMetadata.cs
index f1ebec72f5..9854854aad 100644
--- a/src/ImageSharp/Formats/Cur/CurFrameMetadata.cs
+++ b/src/ImageSharp/Formats/Cur/CurFrameMetadata.cs
@@ -104,7 +104,6 @@ public static CurFrameMetadata FromFormatConnectingFrameMetadata(FormatConnectin
             Compression = compression,
             EncodingWidth = ClampEncodingDimension(metadata.EncodingWidth),
             EncodingHeight = ClampEncodingDimension(metadata.EncodingHeight),
-            ColorTable = compression == IconFrameCompression.Bmp ? metadata.ColorTable : null
         };
     }
 
@@ -113,7 +112,6 @@ public FormatConnectingFrameMetadata ToFormatConnectingFrameMetadata()
         => new()
         {
             PixelTypeInfo = this.GetPixelTypeInfo(),
-            ColorTable = this.ColorTable,
             EncodingWidth = this.EncodingWidth,
             EncodingHeight = this.EncodingHeight
         };
diff --git a/src/ImageSharp/Formats/Cur/CurMetadata.cs b/src/ImageSharp/Formats/Cur/CurMetadata.cs
index 5c725e2916..d8fdb32902 100644
--- a/src/ImageSharp/Formats/Cur/CurMetadata.cs
+++ b/src/ImageSharp/Formats/Cur/CurMetadata.cs
@@ -71,8 +71,7 @@ public static CurMetadata FromFormatConnectingMetadata(FormatConnectingMetadata
         return new CurMetadata
         {
             BmpBitsPerPixel = bbpp,
-            Compression = compression,
-            ColorTable = compression == IconFrameCompression.Bmp ? metadata.ColorTable : null
+            Compression = compression
         };
     }
 
@@ -145,8 +144,7 @@ public FormatConnectingMetadata ToFormatConnectingMetadata()
             EncodingType = this.Compression == IconFrameCompression.Bmp && this.BmpBitsPerPixel <= BmpBitsPerPixel.Bit8
                 ? EncodingType.Lossy
                 : EncodingType.Lossless,
-            PixelTypeInfo = this.GetPixelTypeInfo(),
-            ColorTable = this.ColorTable
+            PixelTypeInfo = this.GetPixelTypeInfo()
         };
 
     /// <inheritdoc/>
diff --git a/src/ImageSharp/Formats/FormatConnectingFrameMetadata.cs b/src/ImageSharp/Formats/FormatConnectingFrameMetadata.cs
index ded220c9ad..15a28c301a 100644
--- a/src/ImageSharp/Formats/FormatConnectingFrameMetadata.cs
+++ b/src/ImageSharp/Formats/FormatConnectingFrameMetadata.cs
@@ -15,11 +15,6 @@ public class FormatConnectingFrameMetadata
     /// </summary>
     public PixelTypeInfo? PixelTypeInfo { get; init; }
 
-    /// <summary>
-    /// Gets the frame color table if any.
-    /// </summary>
-    public ReadOnlyMemory<Color>? ColorTable { get; init; }
-
     /// <summary>
     /// Gets the frame color table mode.
     /// </summary>
diff --git a/src/ImageSharp/Formats/FormatConnectingMetadata.cs b/src/ImageSharp/Formats/FormatConnectingMetadata.cs
index 9cfe40f385..efa7acdc86 100644
--- a/src/ImageSharp/Formats/FormatConnectingMetadata.cs
+++ b/src/ImageSharp/Formats/FormatConnectingMetadata.cs
@@ -28,11 +28,6 @@ public class FormatConnectingMetadata
     /// </summary>
     public PixelTypeInfo PixelTypeInfo { get; init; }
 
-    /// <summary>
-    /// Gets the shared color table if any.
-    /// </summary>
-    public ReadOnlyMemory<Color>? ColorTable { get; init; }
-
     /// <summary>
     /// Gets the shared color table mode.
     /// </summary>
diff --git a/src/ImageSharp/Formats/Gif/GifDecoderCore.cs b/src/ImageSharp/Formats/Gif/GifDecoderCore.cs
index e9012436e9..f6e3643d58 100644
--- a/src/ImageSharp/Formats/Gif/GifDecoderCore.cs
+++ b/src/ImageSharp/Formats/Gif/GifDecoderCore.cs
@@ -90,9 +90,9 @@ internal sealed class GifDecoderCore : ImageDecoderCore
     private GifMetadata? gifMetadata;
 
     /// <summary>
-    /// The background color used to fill the frame.
+    /// The background color index.
     /// </summary>
-    private Color backgroundColor;
+    private byte backgroundColorIndex;
 
     /// <summary>
     /// Initializes a new instance of the <see cref="GifDecoderCore"/> class.
@@ -115,11 +115,11 @@ protected override Image<TPixel> Decode<TPixel>(BufferedReadStream stream, Cance
         ImageFrame<TPixel>? previousFrame = null;
         FrameDisposalMode? previousDisposalMode = null;
         bool globalColorTableUsed = false;
+        Color backgroundColor = Color.Transparent;
 
         try
         {
             this.ReadLogicalScreenDescriptorAndGlobalColorTable(stream);
-            TPixel backgroundPixel = this.backgroundColor.ToPixel<TPixel>();
 
             // Loop though the respective gif parts and read the data.
             int nextFlag = stream.ReadByte();
@@ -132,7 +132,7 @@ protected override Image<TPixel> Decode<TPixel>(BufferedReadStream stream, Cance
                         break;
                     }
 
-                    globalColorTableUsed |= this.ReadFrame(stream, ref image, ref previousFrame, ref previousDisposalMode, backgroundPixel);
+                    globalColorTableUsed |= this.ReadFrame(stream, ref image, ref previousFrame, ref previousDisposalMode, ref backgroundColor);
 
                     // Reset per-frame state.
                     this.imageDescriptor = default;
@@ -442,14 +442,14 @@ private void ReadComments(BufferedReadStream stream)
     /// <param name="image">The image to decode the information to.</param>
     /// <param name="previousFrame">The previous frame.</param>
     /// <param name="previousDisposalMode">The previous frame disposal mode.</param>
-    /// <param name="backgroundPixel">The background color pixel.</param>
+    /// <param name="backgroundColor">The background color.</param>
     /// <returns>Whether the frame has a global color table.</returns>
     private bool ReadFrame<TPixel>(
         BufferedReadStream stream,
         ref Image<TPixel>? image,
         ref ImageFrame<TPixel>? previousFrame,
         ref FrameDisposalMode? previousDisposalMode,
-        TPixel backgroundPixel)
+        ref Color backgroundColor)
         where TPixel : unmanaged, IPixel<TPixel>
     {
         this.ReadImageDescriptor(stream);
@@ -471,7 +471,47 @@ private bool ReadFrame<TPixel>(
         }
 
         ReadOnlySpan<Rgb24> colorTable = MemoryMarshal.Cast<byte, Rgb24>(rawColorTable);
-        this.ReadFrameColors(stream, ref image, ref previousFrame, ref previousDisposalMode, colorTable, backgroundPixel);
+
+        // First frame
+        if (image is null)
+        {
+            if (this.backgroundColorIndex < colorTable.Length)
+            {
+                backgroundColor = Color.FromPixel(colorTable[this.backgroundColorIndex]);
+            }
+            else
+            {
+                backgroundColor = Color.Transparent;
+            }
+
+            if (this.graphicsControlExtension.TransparencyFlag)
+            {
+                backgroundColor = backgroundColor.WithAlpha(0);
+            }
+        }
+
+        this.ReadFrameColors(stream, ref image, ref previousFrame, ref previousDisposalMode, colorTable, backgroundColor.ToPixel<TPixel>());
+
+        // Update from newly decoded frame.
+        if (this.graphicsControlExtension.DisposalMethod != FrameDisposalMode.RestoreToPrevious)
+        {
+            if (this.backgroundColorIndex < colorTable.Length)
+            {
+                backgroundColor = Color.FromPixel(colorTable[this.backgroundColorIndex]);
+            }
+            else
+            {
+                backgroundColor = Color.Transparent;
+            }
+
+            // TODO: I don't understand why this is always set to alpha of zero.
+            // This should be dependent on the transparency flag of the graphics
+            // control extension. ImageMagick does the same.
+            // if (this.graphicsControlExtension.TransparencyFlag)
+            {
+                backgroundColor = backgroundColor.WithAlpha(0);
+            }
+        }
 
         // Skip any remaining blocks
         SkipBlock(stream);
@@ -504,8 +544,9 @@ private void ReadFrameColors<TPixel>(
         bool transFlag = this.graphicsControlExtension.TransparencyFlag;
         FrameDisposalMode disposalMethod = this.graphicsControlExtension.DisposalMethod;
         ImageFrame<TPixel> currentFrame;
+        ImageFrame<TPixel>? restoreFrame = null;
 
-        if (previousFrame is null)
+        if (previousFrame is null && previousDisposalMode is null)
         {
             image = transFlag
                 ? new Image<TPixel>(this.configuration, imageWidth, imageHeight, this.metadata)
@@ -516,26 +557,42 @@ private void ReadFrameColors<TPixel>(
         }
         else
         {
-            // We create a clone of the frame and add it.
-            // We will overpaint the difference of pixels on the current frame to create a complete image.
-            // This ensures that we have enough pixel data to process without distortion. #2450
-            currentFrame = image!.Frames.AddFrame(previousFrame);
+            if (previousFrame != null)
+            {
+                currentFrame = image!.Frames.AddFrame(previousFrame);
+            }
+            else
+            {
+                currentFrame = image!.Frames.CreateFrame(backgroundPixel);
+            }
 
             this.SetFrameMetadata(currentFrame.Metadata);
 
+            if (this.graphicsControlExtension.DisposalMethod == FrameDisposalMode.RestoreToPrevious)
+            {
+                restoreFrame = previousFrame;
+            }
+
             if (previousDisposalMode == FrameDisposalMode.RestoreToBackground)
             {
                 this.RestoreToBackground(currentFrame, backgroundPixel, transFlag);
             }
         }
 
-        Rectangle interest = Rectangle.Intersect(image.Bounds, new(descriptor.Left, descriptor.Top, descriptor.Width, descriptor.Height));
-        previousFrame = currentFrame;
+        if (this.graphicsControlExtension.DisposalMethod == FrameDisposalMode.RestoreToPrevious)
+        {
+            previousFrame = restoreFrame;
+        }
+        else
+        {
+            previousFrame = currentFrame;
+        }
+
         previousDisposalMode = disposalMethod;
 
         if (disposalMethod == FrameDisposalMode.RestoreToBackground)
         {
-            this.restoreArea = interest;
+            this.restoreArea = Rectangle.Intersect(image.Bounds, new(descriptor.Left, descriptor.Top, descriptor.Width, descriptor.Height));
         }
 
         if (colorTable.Length == 0)
@@ -814,19 +871,9 @@ private void ReadLogicalScreenDescriptorAndGlobalColorTable(BufferedReadStream s
             }
         }
 
-        // If the global color table is present, we can set the background color
-        // otherwise we default to transparent to match browser behavior.
-        ReadOnlyMemory<Color>? table = this.gifMetadata.GlobalColorTable;
         byte index = this.logicalScreenDescriptor.BackgroundColorIndex;
-        if (table is not null && index < table.Value.Length)
-        {
-            this.backgroundColor = table.Value.Span[index];
-            this.gifMetadata.BackgroundColorIndex = index;
-        }
-        else
-        {
-            this.backgroundColor = Color.Transparent;
-        }
+        this.backgroundColorIndex = index;
+        this.gifMetadata.BackgroundColorIndex = index;
     }
 
     private unsafe struct ScratchBuffer
diff --git a/src/ImageSharp/Formats/Gif/GifFrameMetadata.cs b/src/ImageSharp/Formats/Gif/GifFrameMetadata.cs
index 92bd114e8f..e1b3354ad2 100644
--- a/src/ImageSharp/Formats/Gif/GifFrameMetadata.cs
+++ b/src/ImageSharp/Formats/Gif/GifFrameMetadata.cs
@@ -1,7 +1,6 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
-using System.Numerics;
 using SixLabors.ImageSharp.PixelFormats;
 
 namespace SixLabors.ImageSharp.Formats.Gif;
@@ -77,34 +76,12 @@ private GifFrameMetadata(GifFrameMetadata other)
 
     /// <inheritdoc />
     public static GifFrameMetadata FromFormatConnectingFrameMetadata(FormatConnectingFrameMetadata metadata)
-    {
-        int index = -1;
-        const float background = 1f;
-        if (metadata.ColorTable.HasValue)
+        => new()
         {
-            ReadOnlySpan<Color> colorTable = metadata.ColorTable.Value.Span;
-            for (int i = 0; i < colorTable.Length; i++)
-            {
-                Vector4 vector = colorTable[i].ToScaledVector4();
-                if (vector.W < background)
-                {
-                    index = i;
-                }
-            }
-        }
-
-        bool hasTransparency = index >= 0;
-
-        return new()
-        {
-            LocalColorTable = metadata.ColorTable,
             ColorTableMode = metadata.ColorTableMode,
             FrameDelay = (int)Math.Round(metadata.Duration.TotalMilliseconds / 10),
             DisposalMode = metadata.DisposalMode,
-            HasTransparency = hasTransparency,
-            TransparencyIndex = hasTransparency ? unchecked((byte)index) : byte.MinValue,
         };
-    }
 
     /// <inheritdoc />
     public FormatConnectingFrameMetadata ToFormatConnectingFrameMetadata()
@@ -118,7 +95,6 @@ public FormatConnectingFrameMetadata ToFormatConnectingFrameMetadata()
 
         return new()
         {
-            ColorTable = this.LocalColorTable,
             ColorTableMode = this.ColorTableMode,
             Duration = TimeSpan.FromMilliseconds(this.FrameDelay * 10),
             DisposalMode = this.DisposalMode,
diff --git a/src/ImageSharp/Formats/Gif/GifMetadata.cs b/src/ImageSharp/Formats/Gif/GifMetadata.cs
index fc6c9ab9a4..77f600633b 100644
--- a/src/ImageSharp/Formats/Gif/GifMetadata.cs
+++ b/src/ImageSharp/Formats/Gif/GifMetadata.cs
@@ -71,32 +71,14 @@ private GifMetadata(GifMetadata other)
 
     /// <inheritdoc/>
     public static GifMetadata FromFormatConnectingMetadata(FormatConnectingMetadata metadata)
-    {
-        int index = 0;
-        Color background = metadata.BackgroundColor;
-        if (metadata.ColorTable.HasValue)
-        {
-            ReadOnlySpan<Color> colorTable = metadata.ColorTable.Value.Span;
-            for (int i = 0; i < colorTable.Length; i++)
-            {
-                if (background != colorTable[i])
-                {
-                    continue;
-                }
-
-                index = i;
-                break;
-            }
-        }
-
-        return new()
+        => new()
         {
-            GlobalColorTable = metadata.ColorTable,
+            // Do not copy the color table or bit depth.
+            // This will lead to a mismatch when the image is comprised of frames
+            // extracted individually from a multi-frame image.
             ColorTableMode = metadata.ColorTableMode,
             RepeatCount = metadata.RepeatCount,
-            BackgroundColorIndex = (byte)Numerics.Clamp(index, 0, 255),
         };
-    }
 
     /// <inheritdoc/>
     public PixelTypeInfo GetPixelTypeInfo()
@@ -114,22 +96,13 @@ public PixelTypeInfo GetPixelTypeInfo()
 
     /// <inheritdoc/>
     public FormatConnectingMetadata ToFormatConnectingMetadata()
-    {
-        bool global = this.ColorTableMode == FrameColorTableMode.Global;
-        Color color = global && this.GlobalColorTable.HasValue && this.GlobalColorTable.Value.Span.Length > this.BackgroundColorIndex
-            ? this.GlobalColorTable.Value.Span[this.BackgroundColorIndex]
-            : Color.Transparent;
-
-        return new FormatConnectingMetadata()
+        => new()
         {
             AnimateRootFrame = true,
-            ColorTable = global ? this.GlobalColorTable : null,
-            BackgroundColor = color,
             ColorTableMode = this.ColorTableMode,
             PixelTypeInfo = this.GetPixelTypeInfo(),
             RepeatCount = this.RepeatCount,
         };
-    }
 
     /// <inheritdoc/>
     public void AfterImageApply<TPixel>(Image<TPixel> destination)
diff --git a/src/ImageSharp/Formats/Ico/IcoFrameMetadata.cs b/src/ImageSharp/Formats/Ico/IcoFrameMetadata.cs
index 77096d5241..31f65133e6 100644
--- a/src/ImageSharp/Formats/Ico/IcoFrameMetadata.cs
+++ b/src/ImageSharp/Formats/Ico/IcoFrameMetadata.cs
@@ -96,8 +96,7 @@ public static IcoFrameMetadata FromFormatConnectingFrameMetadata(FormatConnectin
             BmpBitsPerPixel = bbpp,
             Compression = compression,
             EncodingWidth = ClampEncodingDimension(metadata.EncodingWidth),
-            EncodingHeight = ClampEncodingDimension(metadata.EncodingHeight),
-            ColorTable = compression == IconFrameCompression.Bmp ? metadata.ColorTable : null
+            EncodingHeight = ClampEncodingDimension(metadata.EncodingHeight)
         };
     }
 
@@ -106,7 +105,6 @@ public FormatConnectingFrameMetadata ToFormatConnectingFrameMetadata()
         => new()
         {
             PixelTypeInfo = this.GetPixelTypeInfo(),
-            ColorTable = this.ColorTable,
             EncodingWidth = this.EncodingWidth,
             EncodingHeight = this.EncodingHeight
         };
diff --git a/src/ImageSharp/Formats/Ico/IcoMetadata.cs b/src/ImageSharp/Formats/Ico/IcoMetadata.cs
index 09c1da1b1a..f8c2ff40f2 100644
--- a/src/ImageSharp/Formats/Ico/IcoMetadata.cs
+++ b/src/ImageSharp/Formats/Ico/IcoMetadata.cs
@@ -71,8 +71,7 @@ public static IcoMetadata FromFormatConnectingMetadata(FormatConnectingMetadata
         return new IcoMetadata
         {
             BmpBitsPerPixel = bbpp,
-            Compression = compression,
-            ColorTable = compression == IconFrameCompression.Bmp ? metadata.ColorTable : null
+            Compression = compression
         };
     }
 
@@ -145,8 +144,7 @@ public FormatConnectingMetadata ToFormatConnectingMetadata()
             EncodingType = this.Compression == IconFrameCompression.Bmp && this.BmpBitsPerPixel <= BmpBitsPerPixel.Bit8
                 ? EncodingType.Lossy
                 : EncodingType.Lossless,
-            PixelTypeInfo = this.GetPixelTypeInfo(),
-            ColorTable = this.ColorTable
+            PixelTypeInfo = this.GetPixelTypeInfo()
         };
 
     /// <inheritdoc/>
diff --git a/src/ImageSharp/Formats/Icon/IconEncoderCore.cs b/src/ImageSharp/Formats/Icon/IconEncoderCore.cs
index 03e01f912f..76b14832ae 100644
--- a/src/ImageSharp/Formats/Icon/IconEncoderCore.cs
+++ b/src/ImageSharp/Formats/Icon/IconEncoderCore.cs
@@ -120,17 +120,17 @@ private void InitHeader(Image image)
         this.entries = this.iconFileType switch
         {
             IconFileType.ICO =>
-            image.Frames.Select(i =>
+            [.. image.Frames.Select(i =>
             {
                 IcoFrameMetadata metadata = i.Metadata.GetIcoMetadata();
                 return new EncodingFrameMetadata(metadata.Compression, metadata.BmpBitsPerPixel, metadata.ColorTable, metadata.ToIconDirEntry(i.Size));
-            }).ToArray(),
+            })],
             IconFileType.CUR =>
-            image.Frames.Select(i =>
+            [.. image.Frames.Select(i =>
             {
                 CurFrameMetadata metadata = i.Metadata.GetCurMetadata();
                 return new EncodingFrameMetadata(metadata.Compression, metadata.BmpBitsPerPixel, metadata.ColorTable, metadata.ToIconDirEntry(i.Size));
-            }).ToArray(),
+            })],
             _ => throw new NotSupportedException(),
         };
     }
@@ -149,9 +149,15 @@ private void InitHeader(Image image)
 
         if (metadata.ColorTable is null)
         {
+            int count = metadata.Entry.ColorCount;
+            if (count == 0)
+            {
+                count = 256;
+            }
+
             return new WuQuantizer(new()
             {
-                MaxColors = metadata.Entry.ColorCount
+                MaxColors = count
             });
         }
 
diff --git a/src/ImageSharp/Formats/Png/PngEncoderCore.cs b/src/ImageSharp/Formats/Png/PngEncoderCore.cs
index 3f7f1e5623..b90a9975d3 100644
--- a/src/ImageSharp/Formats/Png/PngEncoderCore.cs
+++ b/src/ImageSharp/Formats/Png/PngEncoderCore.cs
@@ -1570,7 +1570,8 @@ private void SanitizeAndSetEncoderOptions<TPixel>(
             }
             else
             {
-                // Don't use transparency threshold for quantization PNG can handle multiple transparent colors.
+                // Don't use the default transparency threshold for quantization as PNG can handle multiple transparent colors.
+                // We choose a value that is close to zero so that edge cases causes by lower bit depths for the alpha channel are handled correctly.
                 this.quantizer = new WuQuantizer(new QuantizerOptions { TransparencyThreshold = 0, MaxColors = ColorNumerics.GetColorCountForBitDepth(bitDepth) });
             }
         }
diff --git a/src/ImageSharp/Formats/Png/PngMetadata.cs b/src/ImageSharp/Formats/Png/PngMetadata.cs
index bb80438ba0..59ca3b17a0 100644
--- a/src/ImageSharp/Formats/Png/PngMetadata.cs
+++ b/src/ImageSharp/Formats/Png/PngMetadata.cs
@@ -93,25 +93,6 @@ private PngMetadata(PngMetadata other)
     /// <inheritdoc/>
     public static PngMetadata FromFormatConnectingMetadata(FormatConnectingMetadata metadata)
     {
-        // Should the conversion be from a format that uses a 24bit palette entries (gif)
-        // we need to clone and adjust the color table to allow for transparency.
-        Color[]? colorTable = metadata.ColorTable?.ToArray();
-        if (colorTable != null)
-        {
-            for (int i = 0; i < colorTable.Length; i++)
-            {
-                ref Color c = ref colorTable[i];
-                if (c != metadata.BackgroundColor)
-                {
-                    continue;
-                }
-
-                // Png treats background as fully empty
-                c = Color.Transparent;
-                break;
-            }
-        }
-
         PngColorType color;
         PixelColorType colorType = metadata.PixelTypeInfo.ColorType;
 
@@ -152,7 +133,6 @@ public static PngMetadata FromFormatConnectingMetadata(FormatConnectingMetadata
         {
             ColorType = color,
             BitDepth = bitDepth,
-            ColorTable = colorTable,
             RepeatCount = metadata.RepeatCount,
         };
     }
@@ -241,7 +221,6 @@ public PixelTypeInfo GetPixelTypeInfo()
     public FormatConnectingMetadata ToFormatConnectingMetadata()
         => new()
         {
-            ColorTable = this.ColorTable,
             ColorTableMode = FrameColorTableMode.Global,
             PixelTypeInfo = this.GetPixelTypeInfo(),
             RepeatCount = (ushort)Numerics.Clamp(this.RepeatCount, 0, ushort.MaxValue),
diff --git a/src/ImageSharp/Formats/Webp/Lossy/Vp8Decoder.cs b/src/ImageSharp/Formats/Webp/Lossy/Vp8Decoder.cs
index eb4a517511..3c8bafa1b2 100644
--- a/src/ImageSharp/Formats/Webp/Lossy/Vp8Decoder.cs
+++ b/src/ImageSharp/Formats/Webp/Lossy/Vp8Decoder.cs
@@ -69,11 +69,11 @@ public Vp8Decoder(Vp8FrameHeader frameHeader, Vp8PictureHeader pictureHeader, Vp
         this.YuvBuffer = memoryAllocator.Allocate<byte>((WebpConstants.Bps * 17) + (WebpConstants.Bps * 9) + extraY);
         this.CacheY = memoryAllocator.Allocate<byte>((16 * this.CacheYStride) + extraY, AllocationOptions.Clean);
         int cacheUvSize = (16 * this.CacheUvStride) + extraUv;
-        this.CacheU = memoryAllocator.Allocate<byte>(cacheUvSize, AllocationOptions.Clean);
-        this.CacheV = memoryAllocator.Allocate<byte>(cacheUvSize, AllocationOptions.Clean);
-        this.TmpYBuffer = memoryAllocator.Allocate<byte>((int)width, AllocationOptions.Clean);
-        this.TmpUBuffer = memoryAllocator.Allocate<byte>((int)width, AllocationOptions.Clean);
-        this.TmpVBuffer = memoryAllocator.Allocate<byte>((int)width, AllocationOptions.Clean);
+        this.CacheU = memoryAllocator.Allocate<byte>(cacheUvSize);
+        this.CacheV = memoryAllocator.Allocate<byte>(cacheUvSize);
+        this.TmpYBuffer = memoryAllocator.Allocate<byte>((int)width);
+        this.TmpUBuffer = memoryAllocator.Allocate<byte>((int)width);
+        this.TmpVBuffer = memoryAllocator.Allocate<byte>((int)width);
         this.Pixels = memoryAllocator.Allocate<byte>((int)(width * height * 4), AllocationOptions.Clean);
 
 #if DEBUG
diff --git a/src/ImageSharp/Processing/Processors/Quantization/EuclideanPixelMap{TPixel}.cs b/src/ImageSharp/Processing/Processors/Quantization/EuclideanPixelMap{TPixel}.cs
index d11376e3ba..250122e683 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/EuclideanPixelMap{TPixel}.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/EuclideanPixelMap{TPixel}.cs
@@ -116,7 +116,7 @@ private int GetClosestColorSlow(Rgba32 rgba, ref TPixel paletteRef, out TPixel m
         }
 
         // Now I have the index, pop it into the cache for next time
-        this.cache.Add(rgba, (byte)index);
+        this.cache.Add(rgba, (short)index);
         match = Unsafe.Add(ref paletteRef, (uint)index);
 
         return index;
@@ -131,9 +131,11 @@ private int GetClosestColorSlow(Rgba32 rgba, ref TPixel paletteRef, out TPixel m
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     private static float DistanceSquared(Rgba32 a, Rgba32 b)
     {
-        Vector4 va = new(a.R, a.G, a.B, a.A);
-        Vector4 vb = new(b.R, b.G, b.B, b.A);
-        return Vector4.DistanceSquared(va, vb);
+        float deltaR = a.R - b.R;
+        float deltaG = a.G - b.G;
+        float deltaB = a.B - b.B;
+        float deltaA = a.A - b.A;
+        return (deltaR * deltaR) + (deltaG * deltaG) + (deltaB * deltaB) + (deltaA * deltaA);
     }
 
     public void Dispose() => this.cache.Dispose();
diff --git a/tests/ImageSharp.Tests/Formats/Gif/GifDecoderTests.cs b/tests/ImageSharp.Tests/Formats/Gif/GifDecoderTests.cs
index bc6eeedcbe..6593b8df70 100644
--- a/tests/ImageSharp.Tests/Formats/Gif/GifDecoderTests.cs
+++ b/tests/ImageSharp.Tests/Formats/Gif/GifDecoderTests.cs
@@ -34,6 +34,41 @@ public void Decode_VerifyAllFrames<TPixel>(TestImageProvider<TPixel> provider)
         image.CompareToReferenceOutputMultiFrame(provider, ImageComparer.Exact);
     }
 
+    [Theory]
+    [WithFile(TestImages.Gif.AnimatedLoop, PixelTypes.Rgba32)]
+    [WithFile(TestImages.Gif.AnimatedLoopInterlaced, PixelTypes.Rgba32)]
+    public void Decode_Animated<TPixel>(TestImageProvider<TPixel> provider)
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        using Image<TPixel> image = provider.GetImage();
+        image.DebugSaveMultiFrame(provider);
+        image.CompareToReferenceOutputMultiFrame(provider, ImageComparer.Exact);
+    }
+
+    [Theory]
+    [WithFile(TestImages.Gif.AnimatedTransparentNoRestore, PixelTypes.Rgba32)]
+    [WithFile(TestImages.Gif.AnimatedTransparentRestorePrevious, PixelTypes.Rgba32)]
+    [WithFile(TestImages.Gif.AnimatedTransparentLoop, PixelTypes.Rgba32)]
+    [WithFile(TestImages.Gif.AnimatedTransparentFirstFrameRestorePrev, PixelTypes.Rgba32)]
+    public void Decode_Animated_WithTransparency<TPixel>(TestImageProvider<TPixel> provider)
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        using Image<TPixel> image = provider.GetImage();
+        image.DebugSaveMultiFrame(provider);
+        image.CompareToReferenceOutputMultiFrame(provider, ImageComparer.Exact);
+    }
+
+    [Theory]
+    [WithFile(TestImages.Gif.StaticNontransparent, PixelTypes.Rgba32)]
+    [WithFile(TestImages.Gif.StaticTransparent, PixelTypes.Rgba32)]
+    public void Decode_Static_No_Animation<TPixel>(TestImageProvider<TPixel> provider)
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        using Image<TPixel> image = provider.GetImage();
+        image.DebugSave(provider);
+        image.CompareFirstFrameToReferenceOutput(ImageComparer.Exact, provider);
+    }
+
     [Theory]
     [WithFile(TestImages.Gif.Issues.Issue2450_A, PixelTypes.Rgba32)]
     [WithFile(TestImages.Gif.Issues.Issue2450_B, PixelTypes.Rgba32)]
diff --git a/tests/ImageSharp.Tests/Formats/Gif/GifEncoderTests.cs b/tests/ImageSharp.Tests/Formats/Gif/GifEncoderTests.cs
index d219f551b2..748f505cce 100644
--- a/tests/ImageSharp.Tests/Formats/Gif/GifEncoderTests.cs
+++ b/tests/ImageSharp.Tests/Formats/Gif/GifEncoderTests.cs
@@ -422,12 +422,18 @@ public void Encode_WithTransparentColorBehaviorClear_Works()
 
     [Theory]
     [WithFile(TestImages.Gif.Issues.Issue2866, PixelTypes.Rgba32)]
-    public void GifEncoder_CanDecode_Issue2866<TPixel>(TestImageProvider<TPixel> provider)
-    where TPixel : unmanaged, IPixel<TPixel>
+    public void GifEncoder_CanDecode_AndEncode_Issue2866<TPixel>(TestImageProvider<TPixel> provider)
+        where TPixel : unmanaged, IPixel<TPixel>
     {
         using Image<TPixel> image = provider.GetImage();
 
-        // image.DebugSaveMultiFrame(provider);
+        // Save the image for visual inspection.
         provider.Utility.SaveTestOutputFile(image, "gif", new GifEncoder(), "animated");
+
+        // Now compare the debug output with the reference output.
+        // We do this because the gif encoding is lossy and encoding will lead to differences in the 10s of percent.
+        // From the unencoded image, we can see that the image is visually the same.
+        static bool Predicate(int i, int _) => i % 8 == 0; // Image has many frames, only compare a selection of them.
+        image.CompareDebugOutputToReferenceOutputMultiFrame(provider, ImageComparer.Exact, extension: "gif", predicate: Predicate);
     }
 }
diff --git a/tests/ImageSharp.Tests/Formats/Icon/Cur/CurEncoderTests.cs b/tests/ImageSharp.Tests/Formats/Icon/Cur/CurEncoderTests.cs
index bf94e1d489..69c6317a75 100644
--- a/tests/ImageSharp.Tests/Formats/Icon/Cur/CurEncoderTests.cs
+++ b/tests/ImageSharp.Tests/Formats/Icon/Cur/CurEncoderTests.cs
@@ -4,6 +4,7 @@
 using SixLabors.ImageSharp.Formats;
 using SixLabors.ImageSharp.Formats.Cur;
 using SixLabors.ImageSharp.Formats.Ico;
+using SixLabors.ImageSharp.Formats.Png;
 using SixLabors.ImageSharp.PixelFormats;
 using SixLabors.ImageSharp.Tests.TestUtilities.ImageComparison;
 using static SixLabors.ImageSharp.Tests.TestImages.Cur;
@@ -49,8 +50,8 @@ public void CanConvertFromIco<TPixel>(TestImageProvider<TPixel> provider)
         using Image<TPixel> encoded = Image.Load<TPixel>(memStream);
         encoded.DebugSaveMultiFrame(provider);
 
-        // Despite preservation of the palette. The process can still be lossy
-        encoded.CompareToOriginalMultiFrame(provider, ImageComparer.TolerantPercentage(.23f), IcoDecoder.Instance);
+        // Color palettes are not preserved when transcoding.
+        encoded.CompareToOriginalMultiFrame(provider, ImageComparer.TolerantPercentage(.05F), IcoDecoder.Instance);
 
         for (int i = 0; i < image.Frames.Count; i++)
         {
diff --git a/tests/ImageSharp.Tests/Formats/Png/PngEncoderTests.cs b/tests/ImageSharp.Tests/Formats/Png/PngEncoderTests.cs
index 298d5b788e..2a53e4de79 100644
--- a/tests/ImageSharp.Tests/Formats/Png/PngEncoderTests.cs
+++ b/tests/ImageSharp.Tests/Formats/Png/PngEncoderTests.cs
@@ -442,40 +442,42 @@ public void Encode_APng<TPixel>(TestImageProvider<TPixel> provider)
     }
 
     [Theory]
-    [WithFile(TestImages.Gif.Leo, PixelTypes.Rgba32, 0.613F)]
-    [WithFile(TestImages.Gif.Issues.Issue2866, PixelTypes.Rgba32, 1.06F)]
-    public void Encode_AnimatedFormatTransform_FromGif<TPixel>(TestImageProvider<TPixel> provider, float percentage)
+    [WithFile(TestImages.Gif.Leo, PixelTypes.Rgba32)]
+    [WithFile(TestImages.Gif.Issues.Issue2866, PixelTypes.Rgba32)]
+    public void Encode_AnimatedFormatTransform_FromGif<TPixel>(TestImageProvider<TPixel> provider)
         where TPixel : unmanaged, IPixel<TPixel>
     {
-        if (TestEnvironment.RunsOnCI)
+        if (TestEnvironment.RunsOnCI && !TestEnvironment.IsWindows)
         {
             return;
         }
 
         using Image<TPixel> image = provider.GetImage(GifDecoder.Instance);
 
+        // Save the image for visual inspection.
+        provider.Utility.SaveTestOutputFile(image, "png", PngEncoder, "animated");
+
+        // Now compare the debug output with the reference output.
+        // We do this because the transcoding encoding is lossy and encoding will lead to differences.
+        // From the unencoded image, we can see that the image is visually the same.
+        static bool Predicate(int i, int _) => i % 8 == 0; // Image has many frames, only compare a selection of them.
+        image.CompareDebugOutputToReferenceOutputMultiFrame(provider, ImageComparer.Exact, extension: "png", encoder: PngEncoder, predicate: Predicate);
+
+        // Now save the image and load it again to compare the metadata.
         using MemoryStream memStream = new();
         image.Save(memStream, PngEncoder);
         memStream.Position = 0;
 
-        image.DebugSave(provider: provider, extension: "png", encoder: PngEncoder);
-
-        using Image<TPixel> output = Image.Load<TPixel>(memStream);
-
-        // TODO: Find a better way to compare.
-        // The image has been visually checked but the coarse cache used by the palette quantizer
-        // can lead to minor differences between frames.
-        ImageComparer.TolerantPercentage(percentage).VerifySimilarity(output, image);
-
+        using Image<TPixel> encoded = Image.Load<TPixel>(memStream);
         GifMetadata gif = image.Metadata.GetGifMetadata();
-        PngMetadata png = output.Metadata.GetPngMetadata();
+        PngMetadata png = encoded.Metadata.GetPngMetadata();
 
         Assert.Equal(gif.RepeatCount, png.RepeatCount);
 
         for (int i = 0; i < image.Frames.Count; i++)
         {
             GifFrameMetadata gifF = image.Frames[i].Metadata.GetGifMetadata();
-            PngFrameMetadata pngF = output.Frames[i].Metadata.GetPngMetadata();
+            PngFrameMetadata pngF = encoded.Frames[i].Metadata.GetPngMetadata();
 
             Assert.Equal(gifF.FrameDelay, (int)(pngF.FrameDelay.ToDouble() * 100));
 
diff --git a/tests/ImageSharp.Tests/Formats/WebP/WebpEncoderTests.cs b/tests/ImageSharp.Tests/Formats/WebP/WebpEncoderTests.cs
index f82fa65df8..af6f7eea17 100644
--- a/tests/ImageSharp.Tests/Formats/WebP/WebpEncoderTests.cs
+++ b/tests/ImageSharp.Tests/Formats/WebP/WebpEncoderTests.cs
@@ -8,6 +8,8 @@
 using SixLabors.ImageSharp.Formats.Webp;
 using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.PixelFormats;
+using SixLabors.ImageSharp.Processing;
+using SixLabors.ImageSharp.Processing.Processors.Quantization;
 using SixLabors.ImageSharp.Tests.TestUtilities;
 using SixLabors.ImageSharp.Tests.TestUtilities.ImageComparison;
 using SixLabors.ImageSharp.Tests.TestUtilities.ReferenceCodecs;
@@ -110,6 +112,63 @@ public void Encode_AnimatedFormatTransform_FromGif<TPixel>(TestImageProvider<TPi
         }
     }
 
+    [Theory]
+    // [WithFile(AlphaBlend, PixelTypes.Rgba32)]
+    // [WithFile(AlphaBlend2, PixelTypes.Rgba32)]
+    [WithFile(AlphaBlend3, PixelTypes.Rgba32)]
+    // [WithFile(AlphaBlend4, PixelTypes.Rgba32)]
+    public void Encode_AlphaBlended<TPixel>(TestImageProvider<TPixel> provider)
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        using Image<TPixel> image = provider.GetImage();
+        WebpEncoder encoder = new()
+        {
+            FileFormat = WebpFileFormatType.Lossless
+        };
+
+        QuantizerOptions options = new()
+        {
+            TransparencyThreshold = 128 / 255F
+        };
+
+        // First save as gif to gif using different quantizers with default options.
+        // Alpha thresholding is 64/255F.
+        GifEncoder gifEncoder = new()
+        {
+            Quantizer = new OctreeQuantizer(options)
+        };
+        provider.Utility.SaveTestOutputFile(image, "gif", gifEncoder, "octree");
+
+        gifEncoder = new GifEncoder()
+        {
+            Quantizer = new WuQuantizer(options)
+        };
+        provider.Utility.SaveTestOutputFile(image, "gif", gifEncoder, "wu");
+
+        // Now clone and quantize the image using the same quantizers  without alpha thresholding and save as webp.
+        options = new()
+        {
+            TransparencyThreshold = 0
+        };
+
+        using Image<TPixel> cloned1 = image.Clone();
+        cloned1.Mutate(c => c.Quantize(new OctreeQuantizer(options)));
+        provider.Utility.SaveTestOutputFile(cloned1, "webp", encoder, "octree");
+
+        using Image<TPixel> cloned2 = image.Clone();
+        cloned2.Mutate(c => c.Quantize(new WuQuantizer(options)));
+        provider.Utility.SaveTestOutputFile(cloned2, "webp", encoder, "wu");
+
+        // Now blend the images with a blue background and save as webp.
+        using Image<Rgba32> background1 = new(image.Width, image.Height, Color.White.ToPixel<Rgba32>());
+        background1.Mutate(c => c.DrawImage(cloned1, 1));
+        provider.Utility.SaveTestOutputFile(background1, "webp", encoder, "octree-blended");
+
+        using Image<Rgba32> background2 = new(image.Width, image.Height, Color.White.ToPixel<Rgba32>());
+        background2.Mutate(c => c.DrawImage(cloned2, 1));
+        provider.Utility.SaveTestOutputFile(background2, "webp", encoder, "wu-blended");
+    }
+
     [Theory]
     [WithFile(TestImages.Png.APng, PixelTypes.Rgba32)]
     public void Encode_AnimatedFormatTransform_FromPng<TPixel>(TestImageProvider<TPixel> provider)
diff --git a/tests/ImageSharp.Tests/TestImages.cs b/tests/ImageSharp.Tests/TestImages.cs
index 462d54154e..abaec4997c 100644
--- a/tests/ImageSharp.Tests/TestImages.cs
+++ b/tests/ImageSharp.Tests/TestImages.cs
@@ -508,6 +508,31 @@ public static class Gif
         public const string Bit18RGBCube = "Gif/18-bit_RGB_Cube.gif";
         public const string Global256NoTrans = "Gif/global-256-no-trans.gif";
 
+        // Test images from: https://github.com/peterdn/gif-test-suite.git
+        // Animated gif with 4 frames, looping forever, no transparency.
+        public const string AnimatedLoop = "Gif/animated_loop.gif";
+
+        // Animated gif with 4 frames, interlaced, looping forever, no transparency.
+        public const string AnimatedLoopInterlaced = "Gif/animated_loop_interlaced.gif";
+
+        // Transparent gif with 4 frames, loops forever.
+        public const string AnimatedTransparentLoop = "Gif/animated_transparent_loop.gif";
+
+        // Transparent gif with 4 frames, loops forever, first frame restore previous.
+        public const string AnimatedTransparentFirstFrameRestorePrev = "Gif/animated_transparent_firstframerestoreprev_loop.gif";
+
+        // Transparent gif with 4 transparent frames, loops forever, no dispose
+        public const string AnimatedTransparentNoRestore = "Gif/animated_transparent_frame_norestore_loop.gif";
+
+        // Transparent gif with 4 transparent frames, loops forever, restore previous.
+        public const string AnimatedTransparentRestorePrevious = "Gif/animated_transparent_frame_restoreprev_loop.gif";
+
+        // Static gif with no animation, no transparency.
+        public const string StaticNontransparent = "Gif/static_nontransparent.gif";
+
+        // Static transparent gif with no animation.
+        public const string StaticTransparent = "Gif/static_transparent.gif";
+
         // Test images from https://github.com/robert-ancell/pygif/tree/master/test-suite
         public const string ZeroSize = "Gif/image-zero-size.gif";
         public const string ZeroHeight = "Gif/image-zero-height.gif";
@@ -833,6 +858,11 @@ public static class Lossy
             public const string Issue2801 = "Webp/issues/Issue2801.webp";
             public const string Issue2866 = "Webp/issues/Issue2866.webp";
         }
+
+        public const string AlphaBlend = "Webp/alpha-blend.webp";
+        public const string AlphaBlend2 = "Webp/alpha-blend-2.webp";
+        public const string AlphaBlend3 = "Webp/alpha-blend-3.webp";
+        public const string AlphaBlend4 = "Webp/alpha-blend-4.webp";
     }
 
     public static class Tiff
diff --git a/tests/ImageSharp.Tests/TestUtilities/TestImageExtensions.cs b/tests/ImageSharp.Tests/TestUtilities/TestImageExtensions.cs
index 05abedbd8e..263df8f3a6 100644
--- a/tests/ImageSharp.Tests/TestUtilities/TestImageExtensions.cs
+++ b/tests/ImageSharp.Tests/TestUtilities/TestImageExtensions.cs
@@ -107,6 +107,7 @@ public static Image<TPixel> DebugSaveMultiFrame<TPixel>(
         ITestImageProvider provider,
         object testOutputDetails = null,
         string extension = "png",
+        IImageEncoder encoder = null,
         bool appendPixelTypeToFileName = true,
         Func<int, int, bool> predicate = null)
         where TPixel : unmanaged, IPixel<TPixel>
@@ -119,6 +120,7 @@ public static Image<TPixel> DebugSaveMultiFrame<TPixel>(
         provider.Utility.SaveTestOutputFileMultiFrame(
             image,
             extension,
+            encoder: encoder,
             testOutputDetails: testOutputDetails,
             appendPixelTypeToFileName: appendPixelTypeToFileName,
             predicate: predicate);
@@ -277,6 +279,47 @@ public static Image<TPixel> CompareFirstFrameToReferenceOutput<TPixel>(
         return image;
     }
 
+    public static Image<TPixel> CompareDebugOutputToReferenceOutputMultiFrame<TPixel>(
+        this Image<TPixel> image,
+        ITestImageProvider provider,
+        ImageComparer comparer,
+        object testOutputDetails = null,
+        string extension = "png",
+        IImageEncoder encoder = null,
+        bool appendPixelTypeToFileName = true,
+        Func<int, int, bool> predicate = null)
+    where TPixel : unmanaged, IPixel<TPixel>
+    {
+        image.DebugSaveMultiFrame(
+            provider,
+            testOutputDetails,
+            extension,
+            encoder,
+            appendPixelTypeToFileName,
+            predicate: predicate);
+
+        using (Image<TPixel> debugImage = GetDebugOutputImageMultiFrame<TPixel>(
+            provider,
+            image.Frames.Count,
+            testOutputDetails,
+            extension,
+            appendPixelTypeToFileName,
+            predicate: predicate))
+
+        using (Image<TPixel> referenceImage = GetReferenceOutputImageMultiFrame<TPixel>(
+            provider,
+            image.Frames.Count,
+            testOutputDetails,
+            extension,
+            appendPixelTypeToFileName,
+            predicate: predicate))
+        {
+            comparer.VerifySimilarity(referenceImage, debugImage);
+        }
+
+        return image;
+    }
+
     public static Image<TPixel> CompareToReferenceOutputMultiFrame<TPixel>(
         this Image<TPixel> image,
         ITestImageProvider provider,
@@ -375,6 +418,54 @@ public static Image<TPixel> GetReferenceOutputImageMultiFrame<TPixel>(
         return result;
     }
 
+    public static Image<TPixel> GetDebugOutputImageMultiFrame<TPixel>(
+        this ITestImageProvider provider,
+        int frameCount,
+        object testOutputDetails = null,
+        string extension = "png",
+        bool appendPixelTypeToFileName = true,
+        Func<int, int, bool> predicate = null)
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        (int Index, string FileName)[] frameFiles = [.. provider.Utility.GetTestOutputFileNamesMultiFrame(
+            frameCount,
+            extension,
+            testOutputDetails,
+            appendPixelTypeToFileName,
+            predicate: predicate)];
+
+        List<Image<TPixel>> temporaryFrameImages = [];
+
+        IImageDecoder decoder = TestEnvironment.GetReferenceDecoder(frameFiles[0].FileName);
+
+        for (int i = 0; i < frameFiles.Length; i++)
+        {
+            string path = frameFiles[i].FileName;
+            if (!File.Exists(path))
+            {
+                throw new FileNotFoundException("Reference output file missing: " + path);
+            }
+
+            using FileStream stream = File.OpenRead(path);
+            Image<TPixel> tempImage = decoder.Decode<TPixel>(DecoderOptions.Default, stream);
+            temporaryFrameImages.Add(tempImage);
+        }
+
+        Image<TPixel> firstTemp = temporaryFrameImages[0];
+
+        Image<TPixel> result = new(firstTemp.Width, firstTemp.Height);
+
+        foreach (Image<TPixel> fi in temporaryFrameImages)
+        {
+            result.Frames.AddFrame(fi.Frames.RootFrame);
+            fi.Dispose();
+        }
+
+        // Remove the initial empty frame:
+        result.Frames.RemoveFrame(0);
+        return result;
+    }
+
     public static IEnumerable<ImageSimilarityReport> GetReferenceOutputSimilarityReports<TPixel>(
         this Image<TPixel> image,
         ITestImageProvider provider,
diff --git a/tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Animated_Rgba32_animated_loop.gif/00.png b/tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Animated_Rgba32_animated_loop.gif/00.png
new file mode 100644
index 0000000000..65b2c6ff72
--- /dev/null
+++ b/tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Animated_Rgba32_animated_loop.gif/00.png
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:0b980fb1927a70f88bd26b039c54e4ea20a6a1ad68aacd6f1a68a46eb1997a29
+size 1180
diff --git a/tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Animated_Rgba32_animated_loop.gif/01.png b/tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Animated_Rgba32_animated_loop.gif/01.png
new file mode 100644
index 0000000000..8c9e125ade
--- /dev/null
+++ b/tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Animated_Rgba32_animated_loop.gif/01.png
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:4006374b88ff4c4ed665333608a19e693fc083ae72beb71850d0e39ad45c9943
+size 1144
diff --git a/tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Animated_Rgba32_animated_loop.gif/02.png b/tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Animated_Rgba32_animated_loop.gif/02.png
new file mode 100644
index 0000000000..a2fc2ab3bc
--- /dev/null
+++ b/tests/Images/External/ReferenceOutput/GifDecoderTests/Decode_Animated_Rgba32_animated_loop.gif/02.png
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
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new file mode 100644
index 0000000000..bbe754da3d
--- /dev/null
+++ b/tests/Images/External/ReferenceOutput/PngEncoderTests/Encode_AnimatedFormatTransform_FromGif_Rgba32_leo.gif/08.png
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:0ecf0666ca8b0ef16cf0e6147aea4b76af76f62777a62ea02edcf5cf5a309d8b
+size 29721
diff --git a/tests/Images/Input/Gif/animated_loop.gif b/tests/Images/Input/Gif/animated_loop.gif
new file mode 100644
index 0000000000..5fad702a10
--- /dev/null
+++ b/tests/Images/Input/Gif/animated_loop.gif
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:a8750149c953e9e910472684158c07a2cb551c1f7e95744ab48db1a67f63f342
+size 873
diff --git a/tests/Images/Input/Gif/animated_loop_interlaced.gif b/tests/Images/Input/Gif/animated_loop_interlaced.gif
new file mode 100644
index 0000000000..9577a84658
--- /dev/null
+++ b/tests/Images/Input/Gif/animated_loop_interlaced.gif
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:c2bc2f895f03092b1c26381a32b5dd5838aacd3331e07f7e4dae55d5cbb4e149
+size 878
diff --git a/tests/Images/Input/Gif/animated_transparent_firstframerestoreprev_loop.gif b/tests/Images/Input/Gif/animated_transparent_firstframerestoreprev_loop.gif
new file mode 100644
index 0000000000..5012324caf
--- /dev/null
+++ b/tests/Images/Input/Gif/animated_transparent_firstframerestoreprev_loop.gif
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:6b0cf18d386dc979fcf853d6a9adac673a2709a8751d31a94930199dededa25f
+size 536
diff --git a/tests/Images/Input/Gif/animated_transparent_frame_norestore_loop.gif b/tests/Images/Input/Gif/animated_transparent_frame_norestore_loop.gif
new file mode 100644
index 0000000000..712f334aba
--- /dev/null
+++ b/tests/Images/Input/Gif/animated_transparent_frame_norestore_loop.gif
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:ad7359801fa6ed89fb041de1e88faea856b1028d9f477fdc4eda774df6e5f1ce
+size 685
diff --git a/tests/Images/Input/Gif/animated_transparent_frame_restorebackground_loop.gif b/tests/Images/Input/Gif/animated_transparent_frame_restorebackground_loop.gif
new file mode 100644
index 0000000000..b6f675dcaf
--- /dev/null
+++ b/tests/Images/Input/Gif/animated_transparent_frame_restorebackground_loop.gif
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:12254f22eeee9eac6babbfbfb34b6ae9302342454fd6677e8c7c9937656cc127
+size 685
diff --git a/tests/Images/Input/Gif/animated_transparent_frame_restoreprev_loop.gif b/tests/Images/Input/Gif/animated_transparent_frame_restoreprev_loop.gif
new file mode 100644
index 0000000000..be7fdf85d8
--- /dev/null
+++ b/tests/Images/Input/Gif/animated_transparent_frame_restoreprev_loop.gif
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:0cdfba6efea653bb94ede6edd0577ba6af1f7c130307b94903dd94f0f8bbc4f9
+size 685
diff --git a/tests/Images/Input/Gif/animated_transparent_loop.gif b/tests/Images/Input/Gif/animated_transparent_loop.gif
new file mode 100644
index 0000000000..cb001ece8f
--- /dev/null
+++ b/tests/Images/Input/Gif/animated_transparent_loop.gif
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:3297987894ba27c2acc6a5c447c3d3a52cc169447b451409535decccc1743e55
+size 536
diff --git a/tests/Images/Input/Gif/animated_transparent_restoreprev_loop.gif b/tests/Images/Input/Gif/animated_transparent_restoreprev_loop.gif
new file mode 100644
index 0000000000..f51d02433e
--- /dev/null
+++ b/tests/Images/Input/Gif/animated_transparent_restoreprev_loop.gif
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:9418561ef2f2307456bb068ecc1a9d5aa02da5e314e7aadd722985e27503926b
+size 536
diff --git a/tests/Images/Input/Gif/static_nontransparent.gif b/tests/Images/Input/Gif/static_nontransparent.gif
new file mode 100644
index 0000000000..17ab1e2ec7
--- /dev/null
+++ b/tests/Images/Input/Gif/static_nontransparent.gif
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:d0a5e1b2f0c5c1763eb950a1d92c5317f048875e04e88dca7f1a966552c2774c
+size 678
diff --git a/tests/Images/Input/Gif/static_transparent.gif b/tests/Images/Input/Gif/static_transparent.gif
new file mode 100644
index 0000000000..89039a732a
--- /dev/null
+++ b/tests/Images/Input/Gif/static_transparent.gif
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:f73f56bbe2206bd1cd8a4625b6a4d61506214b37b61ff3e8194e2030b28abca5
+size 341
diff --git a/tests/Images/Input/Webp/alpha-blend-2.webp b/tests/Images/Input/Webp/alpha-blend-2.webp
new file mode 100644
index 0000000000..3ca4c77cff
--- /dev/null
+++ b/tests/Images/Input/Webp/alpha-blend-2.webp
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:b07a49ab8b3af82fa123faf897ec537cd26d57175b1d6301b617372c06432899
+size 1580484
diff --git a/tests/Images/Input/Webp/alpha-blend-3.webp b/tests/Images/Input/Webp/alpha-blend-3.webp
new file mode 100644
index 0000000000..1922f561d5
--- /dev/null
+++ b/tests/Images/Input/Webp/alpha-blend-3.webp
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:b7244a2cfb42285a196fc7846c49da65fac47e5b85f735bc07b131707c8a2d46
+size 948
diff --git a/tests/Images/Input/Webp/alpha-blend-4.webp b/tests/Images/Input/Webp/alpha-blend-4.webp
new file mode 100644
index 0000000000..6f4db231f6
--- /dev/null
+++ b/tests/Images/Input/Webp/alpha-blend-4.webp
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:8c8b98f188d006715bd5bc60593ff2a379078f28a7fc14a51d28ae1cfb279aac
+size 2185502
diff --git a/tests/Images/Input/Webp/alpha-blend.webp b/tests/Images/Input/Webp/alpha-blend.webp
new file mode 100644
index 0000000000..110d2a594c
--- /dev/null
+++ b/tests/Images/Input/Webp/alpha-blend.webp
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:5dc2762d1c1030fb951e1af57eaa7e66035a7b5e63bd9dc9f9bd50f0ff5c4c3a
+size 1297692

From 4aae44fdd94a81f8dd1dd95e224288cbc0a55dbc Mon Sep 17 00:00:00 2001
From: James Jackson-South <james_south@hotmail.com>
Date: Tue, 18 Mar 2025 20:09:41 +1000
Subject: [PATCH 06/18] Pass readonly region

---
 src/ImageSharp/Formats/Png/PngEncoderCore.cs             | 9 +++++----
 .../Processors/Quantization/QuantizerUtilities.cs        | 2 +-
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/src/ImageSharp/Formats/Png/PngEncoderCore.cs b/src/ImageSharp/Formats/Png/PngEncoderCore.cs
index b90a9975d3..fea9e801c6 100644
--- a/src/ImageSharp/Formats/Png/PngEncoderCore.cs
+++ b/src/ImageSharp/Formats/Png/PngEncoderCore.cs
@@ -1584,14 +1584,15 @@ private void SanitizeAndSetEncoderOptions<TPixel>(
             // Encoding animated frames with a global palette requires a transparent pixel in the palette
             // since we only encode the delta between frames. To ensure that we have a transparent pixel
             // we create a fake frame with a containing only transparent pixels and add it to the palette.
-            using Buffer2D<TPixel> px = image.Configuration.MemoryAllocator.Allocate2D<TPixel>(Math.Min(256, image.Width), Math.Min(256, image.Height));
+            using Buffer2D<TPixel> fake = image.Configuration.MemoryAllocator.Allocate2D<TPixel>(Math.Min(256, image.Width), Math.Min(256, image.Height));
             TPixel backGroundPixel = backgroundColor.ToPixel<TPixel>();
-            for (int i = 0; i < px.Height; i++)
+            for (int i = 0; i < fake.Height; i++)
             {
-                px.DangerousGetRowSpan(i).Fill(backGroundPixel);
+                fake.DangerousGetRowSpan(i).Fill(backGroundPixel);
             }
 
-            frameQuantizer.AddPaletteColors(px.GetRegion());
+            Buffer2DRegion<TPixel> fakeRegion = fake.GetRegion();
+            frameQuantizer.AddPaletteColors(in fakeRegion);
         }
 
         frameQuantizer.BuildPalette(
diff --git a/src/ImageSharp/Processing/Processors/Quantization/QuantizerUtilities.cs b/src/ImageSharp/Processing/Processors/Quantization/QuantizerUtilities.cs
index 7669f0d3c6..49eaa79abb 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/QuantizerUtilities.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/QuantizerUtilities.cs
@@ -55,7 +55,7 @@ public static IndexedImageFrame<TPixel> BuildPaletteAndQuantizeFrame<TPixel>(
         Buffer2DRegion<TPixel> region = source.PixelBuffer.GetRegion(interest);
 
         // Collect the palette. Required before the second pass runs.
-        quantizer.AddPaletteColors(region);
+        quantizer.AddPaletteColors(in region);
         return quantizer.QuantizeFrame(source, bounds);
     }
 

From 6322bcb7d5b7e0563bffd20424e6f43d44a05d81 Mon Sep 17 00:00:00 2001
From: James Jackson-South <james_south@hotmail.com>
Date: Thu, 27 Mar 2025 09:38:40 +1000
Subject: [PATCH 07/18] Use different cache types and begin to make quantizers
 own clearing pixels.

---
 src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs  |   7 +-
 src/ImageSharp/Formats/EncodingUtilities.cs   | 119 +++-
 src/ImageSharp/Formats/Gif/GifEncoderCore.cs  |  28 +-
 .../Formats/IAnimatedImageEncoder.cs          |   6 +-
 .../Formats/ISpecializedDecoderOptions.cs     |   2 +-
 src/ImageSharp/Formats/Png/PngEncoder.cs      |   5 -
 src/ImageSharp/Formats/Png/PngEncoderCore.cs  |  23 +-
 src/ImageSharp/Formats/Qoi/QoiEncoderCore.cs  |   4 +-
 src/ImageSharp/Formats/Tga/TgaEncoderCore.cs  |   4 +-
 .../Formats/Tiff/TiffEncoderCore.cs           |   4 +-
 src/ImageSharp/IndexedImageFrame{TPixel}.cs   |   4 +-
 ...nownTypes.cs => ErrorDither.KnownTypes.cs} |   0
 .../PaletteDitherProcessor{TPixel}.cs         |   4 +-
 .../Quantization/ColorMatchingMode.cs         |  28 +
 .../EuclideanPixelMap{TPixel,TCache}.cs       | 184 ++++++
 .../Quantization/EuclideanPixelMap{TPixel}.cs | 545 ------------------
 .../Quantization/IColorIndexCache.cs          | 491 ++++++++++++++++
 .../Processors/Quantization/IQuantizer.cs     |   6 +-
 .../Quantization/IQuantizer{TPixel}.cs        |  35 +-
 .../IQuantizingPixelRowDelegate{TPixel}.cs    |  27 +
 .../Quantization/OctreeQuantizer{TPixel}.cs   | 121 ++--
 .../Quantization/PaletteQuantizer{TPixel}.cs  |  21 +-
 .../Quantization/QuantizerOptions.cs          |  11 +
 .../Quantization/QuantizerUtilities.cs        | 365 ++++++++++--
 .../Quantization/WuQuantizer{TPixel}.cs       | 118 ++--
 .../Formats/Gif/GifEncoderTests.cs            |   2 +-
 .../Formats/Png/PngEncoderTests.cs            |   4 +-
 27 files changed, 1363 insertions(+), 805 deletions(-)
 rename src/ImageSharp/Processing/Processors/Dithering/{ErroDither.KnownTypes.cs => ErrorDither.KnownTypes.cs} (100%)
 create mode 100644 src/ImageSharp/Processing/Processors/Quantization/ColorMatchingMode.cs
 create mode 100644 src/ImageSharp/Processing/Processors/Quantization/EuclideanPixelMap{TPixel,TCache}.cs
 delete mode 100644 src/ImageSharp/Processing/Processors/Quantization/EuclideanPixelMap{TPixel}.cs
 create mode 100644 src/ImageSharp/Processing/Processors/Quantization/IColorIndexCache.cs
 create mode 100644 src/ImageSharp/Processing/Processors/Quantization/IQuantizingPixelRowDelegate{TPixel}.cs

diff --git a/src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs b/src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs
index 321a559b1e..6a88f080d9 100644
--- a/src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs
+++ b/src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs
@@ -362,10 +362,13 @@ private void WriteImage<TPixel>(
         ImageFrame<TPixel>? clonedFrame = null;
         try
         {
-            if (EncodingUtilities.ShouldClearTransparentPixels<TPixel>(this.transparentColorMode))
+            // No need to clone when quantizing. The quantizer will do it for us.
+            // TODO: We should really try to avoid the clone entirely.
+            int bpp = this.bitsPerPixel != null ? (int)this.bitsPerPixel : 32;
+            if (bpp > 8 && EncodingUtilities.ShouldReplaceTransparentPixels<TPixel>(this.transparentColorMode))
             {
                 clonedFrame = image.Frames.RootFrame.Clone();
-                EncodingUtilities.ClearTransparentPixels(clonedFrame, Color.Transparent);
+                EncodingUtilities.ReplaceTransparentPixels(clonedFrame, Color.Transparent);
             }
 
             ImageFrame<TPixel> encodingFrame = clonedFrame ?? image.Frames.RootFrame;
diff --git a/src/ImageSharp/Formats/EncodingUtilities.cs b/src/ImageSharp/Formats/EncodingUtilities.cs
index db951b1c33..130dd567eb 100644
--- a/src/ImageSharp/Formats/EncodingUtilities.cs
+++ b/src/ImageSharp/Formats/EncodingUtilities.cs
@@ -4,6 +4,7 @@
 using System.Buffers;
 using System.Numerics;
 using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
 using System.Runtime.Intrinsics;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;
@@ -15,50 +16,52 @@ namespace SixLabors.ImageSharp.Formats;
 /// </summary>
 internal static class EncodingUtilities
 {
-    public static bool ShouldClearTransparentPixels<TPixel>(TransparentColorMode mode)
+    /// <summary>
+    /// Determines if transparent pixels can be replaced based on the specified color mode and pixel type.
+    /// </summary>
+    /// <typeparam name="TPixel">The type of the pixel.</typeparam>
+    /// <param name="mode">Indicates the color mode used to assess the ability to replace transparent pixels.</param>
+    /// <returns>Returns true if transparent pixels can be replaced; otherwise, false.</returns>
+    public static bool ShouldReplaceTransparentPixels<TPixel>(TransparentColorMode mode)
         where TPixel : unmanaged, IPixel<TPixel>
-        => mode == TransparentColorMode.Clear &&
-                   TPixel.GetPixelTypeInfo().AlphaRepresentation == PixelAlphaRepresentation.Unassociated;
+        => mode == TransparentColorMode.Clear && TPixel.GetPixelTypeInfo().AlphaRepresentation == PixelAlphaRepresentation.Unassociated;
 
     /// <summary>
-    /// Convert transparent pixels, to pixels represented by <paramref name="color"/>, which can yield
-    /// to better compression in some cases.
+    /// Replaces transparent pixels with pixels represented by <paramref name="color"/>.
     /// </summary>
     /// <typeparam name="TPixel">The type of the pixel.</typeparam>
     /// <param name="frame">The <see cref="ImageFrame{TPixel}"/> where the transparent pixels will be changed.</param>
     /// <param name="color">The color to replace transparent pixels with.</param>
-    public static void ClearTransparentPixels<TPixel>(ImageFrame<TPixel> frame, Color color)
+    public static void ReplaceTransparentPixels<TPixel>(ImageFrame<TPixel> frame, Color color)
         where TPixel : unmanaged, IPixel<TPixel>
-        => ClearTransparentPixels(frame.Configuration, frame.PixelBuffer, color);
+        => ReplaceTransparentPixels(frame.Configuration, frame.PixelBuffer, color);
 
     /// <summary>
-    /// Convert transparent pixels, to pixels represented by <paramref name="color"/>, which can yield
-    /// to better compression in some cases.
+    /// Replaces transparent pixels with pixels represented by <paramref name="color"/>.
     /// </summary>
     /// <typeparam name="TPixel">The type of the pixel.</typeparam>
     /// <param name="configuration">The configuration.</param>
     /// <param name="buffer">The  <see cref="Buffer2D{TPixel}"/> where the transparent pixels will be changed.</param>
     /// <param name="color">The color to replace transparent pixels with.</param>
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public static void ClearTransparentPixels<TPixel>(
+    public static void ReplaceTransparentPixels<TPixel>(
         Configuration configuration,
         Buffer2D<TPixel> buffer,
         Color color)
         where TPixel : unmanaged, IPixel<TPixel>
     {
         Buffer2DRegion<TPixel> region = buffer.GetRegion();
-        ClearTransparentPixels(configuration, in region, color);
+        ReplaceTransparentPixels(configuration, in region, color);
     }
 
     /// <summary>
-    /// Convert transparent pixels, to pixels represented by <paramref name="color"/>, which can yield
-    /// to better compression in some cases.
+    /// Replaces transparent pixels with pixels represented by <paramref name="color"/>.
     /// </summary>
     /// <typeparam name="TPixel">The type of the pixel.</typeparam>
     /// <param name="configuration">The configuration.</param>
     /// <param name="region">The <see cref="Buffer2DRegion{T}"/> where the transparent pixels will be changed.</param>
     /// <param name="color">The color to replace transparent pixels with.</param>
-    public static void ClearTransparentPixels<TPixel>(
+    public static void ReplaceTransparentPixels<TPixel>(
         Configuration configuration,
         in Buffer2DRegion<TPixel> region,
         Color color)
@@ -71,20 +74,92 @@ public static void ClearTransparentPixels<TPixel>(
         {
             Span<TPixel> span = region.DangerousGetRowSpan(y);
             PixelOperations<TPixel>.Instance.ToVector4(configuration, span, vectorsSpan, PixelConversionModifiers.Scale);
-            ClearTransparentPixelRow(vectorsSpan, replacement);
+            ReplaceTransparentPixels(vectorsSpan, replacement);
             PixelOperations<TPixel>.Instance.FromVector4Destructive(configuration, vectorsSpan, span, PixelConversionModifiers.Scale);
         }
     }
 
-    private static void ClearTransparentPixelRow(Span<Vector4> vectorsSpan, Vector4 replacement)
+    /// <summary>
+    /// Replaces transparent pixels with pixels represented by <paramref name="replacement"/>.
+    /// </summary>
+    /// <param name="source">A span of color vectors that will be checked for transparency and potentially modified.</param>
+    /// <param name="replacement">A color vector that will replace transparent pixels when the alpha value is below the specified threshold.</param>
+    public static void ReplaceTransparentPixels(Span<Vector4> source, Vector4 replacement)
     {
-        if (Vector128.IsHardwareAccelerated)
+        if (Vector512.IsHardwareAccelerated && source.Length >= 4)
+        {
+            Vector128<float> replacement128 = replacement.AsVector128();
+            Vector256<float> replacement256 = Vector256.Create(replacement128, replacement128);
+            Vector512<float> replacement512 = Vector512.Create(replacement256, replacement256);
+
+            Span<Vector512<float>> source512 = MemoryMarshal.Cast<Vector4, Vector512<float>>(source);
+            for (int i = 0; i < source512.Length; i++)
+            {
+                ref Vector512<float> v = ref source512[i];
+
+                // Do `vector < threshold`
+                Vector512<float> mask = Vector512.Equals(v, Vector512<float>.Zero);
+
+                // Replicate the result for W to all elements (is AllBitsSet if the W was 0 and Zero otherwise)
+                mask = Vector512.Shuffle(mask, Vector512.Create(3, 3, 3, 3, 7, 7, 7, 7, 11, 11, 11, 11, 15, 15, 15, 15));
+
+                // Use the mask to select the replacement vector
+                // (replacement & mask) | (v512 & ~mask)
+                v = Vector512.ConditionalSelect(mask, replacement512, v);
+            }
+
+            int m = Numerics.Modulo4(source.Length);
+            if (m != 0)
+            {
+                for (int i = source.Length - m; i < source.Length; i++)
+                {
+                    if (source[i].W == 0)
+                    {
+                        source[i] = replacement;
+                    }
+                }
+            }
+        }
+        else if (Vector256.IsHardwareAccelerated && source.Length >= 2)
+        {
+            Vector128<float> replacement128 = replacement.AsVector128();
+            Vector256<float> replacement256 = Vector256.Create(replacement128, replacement128);
+
+            Span<Vector256<float>> source256 = MemoryMarshal.Cast<Vector4, Vector256<float>>(source);
+            for (int i = 0; i < source256.Length; i++)
+            {
+                ref Vector256<float> v = ref source256[i];
+
+                // Do `vector < threshold`
+                Vector256<float> mask = Vector256.Equals(v, Vector256<float>.Zero);
+
+                // Replicate the result for W to all elements (is AllBitsSet if the W was 0 and Zero otherwise)
+                mask = Vector256.Shuffle(mask, Vector256.Create(3, 3, 3, 3, 7, 7, 7, 7));
+
+                // Use the mask to select the replacement vector
+                // (replacement & mask) | (v256 & ~mask)
+                v = Vector256.ConditionalSelect(mask, replacement256, v);
+            }
+
+            int m = Numerics.Modulo2(source.Length);
+            if (m != 0)
+            {
+                for (int i = source.Length - m; i < source.Length; i++)
+                {
+                    if (source[i].W == 0)
+                    {
+                        source[i] = replacement;
+                    }
+                }
+            }
+        }
+        else if (Vector128.IsHardwareAccelerated)
         {
             Vector128<float> replacement128 = replacement.AsVector128();
 
-            for (int i = 0; i < vectorsSpan.Length; i++)
+            for (int i = 0; i < source.Length; i++)
             {
-                ref Vector4 v = ref vectorsSpan[i];
+                ref Vector4 v = ref source[i];
                 Vector128<float> v128 = v.AsVector128();
 
                 // Do `vector == 0`
@@ -100,11 +175,11 @@ private static void ClearTransparentPixelRow(Span<Vector4> vectorsSpan, Vector4
         }
         else
         {
-            for (int i = 0; i < vectorsSpan.Length; i++)
+            for (int i = 0; i < source.Length; i++)
             {
-                if (vectorsSpan[i].W == 0F)
+                if (source[i].W == 0F)
                 {
-                    vectorsSpan[i] = replacement;
+                    source[i] = replacement;
                 }
             }
         }
diff --git a/src/ImageSharp/Formats/Gif/GifEncoderCore.cs b/src/ImageSharp/Formats/Gif/GifEncoderCore.cs
index a4830d7793..eff33f2d1c 100644
--- a/src/ImageSharp/Formats/Gif/GifEncoderCore.cs
+++ b/src/ImageSharp/Formats/Gif/GifEncoderCore.cs
@@ -151,35 +151,20 @@ public void Encode<TPixel>(Image<TPixel> image, Stream stream, CancellationToken
         Color background = Color.Transparent;
         using (IQuantizer<TPixel> frameQuantizer = this.quantizer.CreatePixelSpecificQuantizer<TPixel>(this.configuration))
         {
-            ImageFrame<TPixel>? clonedFrame = null;
-            Configuration configuration = this.configuration;
             TransparentColorMode mode = this.transparentColorMode;
             IPixelSamplingStrategy strategy = this.pixelSamplingStrategy;
-            if (EncodingUtilities.ShouldClearTransparentPixels<TPixel>(mode))
-            {
-                clonedFrame = image.Frames.RootFrame.Clone();
-
-                GifFrameMetadata frameMeta = clonedFrame.Metadata.GetGifMetadata();
-                if (frameMeta.DisposalMode == FrameDisposalMode.RestoreToBackground)
-                {
-                    background = this.backgroundColor ?? Color.Transparent;
-                }
-
-                EncodingUtilities.ClearTransparentPixels(clonedFrame, background);
-            }
-
-            ImageFrame<TPixel> encodingFrame = clonedFrame ?? image.Frames.RootFrame;
 
+            ImageFrame<TPixel> encodingFrame = image.Frames.RootFrame;
             if (useGlobalTableForFirstFrame)
             {
                 if (useGlobalTable)
                 {
-                    frameQuantizer.BuildPalette(configuration, mode, strategy, image, background);
+                    frameQuantizer.BuildPalette(mode, strategy, image);
                     quantized = frameQuantizer.QuantizeFrame(encodingFrame, image.Bounds);
                 }
                 else
                 {
-                    frameQuantizer.BuildPalette(configuration, mode, strategy, encodingFrame, background);
+                    frameQuantizer.BuildPalette(mode, strategy, encodingFrame);
                     quantized = frameQuantizer.QuantizeFrame(encodingFrame, encodingFrame.Bounds);
                 }
             }
@@ -195,8 +180,6 @@ public void Encode<TPixel>(Image<TPixel> image, Stream stream, CancellationToken
                     frameMetadata.HasTransparency ? frameMetadata.TransparencyIndex : -1,
                     background);
             }
-
-            clonedFrame?.Dispose();
         }
 
         // Write the header.
@@ -403,11 +386,6 @@ private void EncodeAdditionalFrame<TPixel>(
                 background,
                 true);
 
-        if (EncodingUtilities.ShouldClearTransparentPixels<TPixel>(this.transparentColorMode))
-        {
-            EncodingUtilities.ClearTransparentPixels(encodingFrame, background);
-        }
-
         using IndexedImageFrame<TPixel> quantized = this.QuantizeAdditionalFrameAndUpdateMetadata(
                 encodingFrame,
                 bounds,
diff --git a/src/ImageSharp/Formats/IAnimatedImageEncoder.cs b/src/ImageSharp/Formats/IAnimatedImageEncoder.cs
index d2c3ad6907..26f2114df2 100644
--- a/src/ImageSharp/Formats/IAnimatedImageEncoder.cs
+++ b/src/ImageSharp/Formats/IAnimatedImageEncoder.cs
@@ -14,17 +14,17 @@ public interface IAnimatedImageEncoder
     /// as well as the transparent pixels of the first frame.
     /// The background color is also used when a frame disposal mode is <see cref="FrameDisposalMode.RestoreToBackground"/>.
     /// </summary>
-    Color? BackgroundColor { get; }
+    public Color? BackgroundColor { get; }
 
     /// <summary>
     /// Gets the number of times any animation is repeated in supported encoders.
     /// </summary>
-    ushort? RepeatCount { get; }
+    public ushort? RepeatCount { get; }
 
     /// <summary>
     /// Gets a value indicating whether the root frame is shown as part of the animated sequence in supported encoders.
     /// </summary>
-    bool? AnimateRootFrame { get; }
+    public bool? AnimateRootFrame { get; }
 }
 
 /// <summary>
diff --git a/src/ImageSharp/Formats/ISpecializedDecoderOptions.cs b/src/ImageSharp/Formats/ISpecializedDecoderOptions.cs
index e0a4c9b62c..881b5bcd44 100644
--- a/src/ImageSharp/Formats/ISpecializedDecoderOptions.cs
+++ b/src/ImageSharp/Formats/ISpecializedDecoderOptions.cs
@@ -11,5 +11,5 @@ public interface ISpecializedDecoderOptions
     /// <summary>
     /// Gets the general decoder options.
     /// </summary>
-    DecoderOptions GeneralOptions { get; init; }
+    public DecoderOptions GeneralOptions { get; init; }
 }
diff --git a/src/ImageSharp/Formats/Png/PngEncoder.cs b/src/ImageSharp/Formats/Png/PngEncoder.cs
index 1032f88529..b6031c1640 100644
--- a/src/ImageSharp/Formats/Png/PngEncoder.cs
+++ b/src/ImageSharp/Formats/Png/PngEncoder.cs
@@ -41,11 +41,6 @@ public class PngEncoder : QuantizingAnimatedImageEncoder
     /// <value>The gamma value of the image.</value>
     public float? Gamma { get; init; }
 
-    /// <summary>
-    /// Gets the transparency threshold.
-    /// </summary>
-    public byte Threshold { get; init; } = byte.MaxValue;
-
     /// <summary>
     /// Gets a value indicating whether this instance should write an Adam7 interlaced image.
     /// </summary>
diff --git a/src/ImageSharp/Formats/Png/PngEncoderCore.cs b/src/ImageSharp/Formats/Png/PngEncoderCore.cs
index fea9e801c6..c05c7e8289 100644
--- a/src/ImageSharp/Formats/Png/PngEncoderCore.cs
+++ b/src/ImageSharp/Formats/Png/PngEncoderCore.cs
@@ -189,12 +189,15 @@ public void Encode<TPixel>(Image<TPixel> image, Stream stream, CancellationToken
         {
             int currentFrameIndex = 0;
 
-            bool clearTransparency = EncodingUtilities.ShouldClearTransparentPixels<TPixel>(this.encoder.TransparentColorMode);
-            if (clearTransparency)
+            bool clearTransparency = EncodingUtilities.ShouldReplaceTransparentPixels<TPixel>(this.encoder.TransparentColorMode);
+
+            // No need to clone when quantizing. The quantizer will do it for us.
+            // TODO: We should really try to avoid the clone entirely.
+            if (clearTransparency && this.colorType is not PngColorType.Palette)
             {
                 currentFrame = clonedFrame = currentFrame.Clone();
                 currentFrameRegion = currentFrame.PixelBuffer.GetRegion();
-                EncodingUtilities.ClearTransparentPixels(this.configuration, in currentFrameRegion, this.backgroundColor.Value);
+                EncodingUtilities.ReplaceTransparentPixels(this.configuration, in currentFrameRegion, this.backgroundColor.Value);
             }
 
             // Do not move this. We require an accurate bit depth for the header chunk.
@@ -286,6 +289,7 @@ public void Encode<TPixel>(Image<TPixel> image, Stream stream, CancellationToken
                     ImageFrame<TPixel>? nextFrame = currentFrameIndex < image.Frames.Count - 1 ? image.Frames[currentFrameIndex + 1] : null;
 
                     frameMetadata = currentFrame.Metadata.GetPngMetadata();
+
                     bool blend = frameMetadata.BlendMode == FrameBlendMode.Over;
                     Color background = frameMetadata.DisposalMode == FrameDisposalMode.RestoreToBackground
                         ? this.backgroundColor.Value
@@ -301,9 +305,9 @@ public void Encode<TPixel>(Image<TPixel> image, Stream stream, CancellationToken
                             background,
                             blend);
 
-                    if (clearTransparency)
+                    if (clearTransparency && this.colorType is not PngColorType.Palette)
                     {
-                        EncodingUtilities.ClearTransparentPixels(encodingFrame, background);
+                        EncodingUtilities.ReplaceTransparentPixels(encodingFrame, background);
                     }
 
                     // Each frame control sequence number must be incremented by the number of frame data chunks that follow.
@@ -779,11 +783,6 @@ private void WritePaletteChunk<TPixel>(Stream stream, IndexedImageFrame<TPixel>?
             byte alpha = rgba.A;
 
             Unsafe.Add(ref colorTableRef, (uint)i) = rgba.Rgb;
-            if (alpha > this.encoder.Threshold)
-            {
-                alpha = byte.MaxValue;
-            }
-
             hasAlpha = hasAlpha || alpha < byte.MaxValue;
             Unsafe.Add(ref alphaTableRef, (uint)i) = alpha;
         }
@@ -1596,11 +1595,9 @@ private void SanitizeAndSetEncoderOptions<TPixel>(
         }
 
         frameQuantizer.BuildPalette(
-            this.configuration,
             encoder.TransparentColorMode,
             encoder.PixelSamplingStrategy,
-            image,
-            backgroundColor);
+            image);
 
         return frameQuantizer.QuantizeFrame(frame, bounds);
     }
diff --git a/src/ImageSharp/Formats/Qoi/QoiEncoderCore.cs b/src/ImageSharp/Formats/Qoi/QoiEncoderCore.cs
index 872cec3fd0..916830273a 100644
--- a/src/ImageSharp/Formats/Qoi/QoiEncoderCore.cs
+++ b/src/ImageSharp/Formats/Qoi/QoiEncoderCore.cs
@@ -90,10 +90,10 @@ private void WritePixels<TPixel>(Image<TPixel> image, Stream stream, Cancellatio
         ImageFrame<TPixel>? clonedFrame = null;
         try
         {
-            if (EncodingUtilities.ShouldClearTransparentPixels<TPixel>(this.encoder.TransparentColorMode))
+            if (EncodingUtilities.ShouldReplaceTransparentPixels<TPixel>(this.encoder.TransparentColorMode))
             {
                 clonedFrame = image.Frames.RootFrame.Clone();
-                EncodingUtilities.ClearTransparentPixels(clonedFrame, Color.Transparent);
+                EncodingUtilities.ReplaceTransparentPixels(clonedFrame, Color.Transparent);
             }
 
             ImageFrame<TPixel> encodingFrame = clonedFrame ?? image.Frames.RootFrame;
diff --git a/src/ImageSharp/Formats/Tga/TgaEncoderCore.cs b/src/ImageSharp/Formats/Tga/TgaEncoderCore.cs
index e2ea9c4fe7..17259629ae 100644
--- a/src/ImageSharp/Formats/Tga/TgaEncoderCore.cs
+++ b/src/ImageSharp/Formats/Tga/TgaEncoderCore.cs
@@ -110,10 +110,10 @@ public void Encode<TPixel>(Image<TPixel> image, Stream stream, CancellationToken
         ImageFrame<TPixel>? clonedFrame = null;
         try
         {
-            if (EncodingUtilities.ShouldClearTransparentPixels<TPixel>(this.transparentColorMode))
+            if (EncodingUtilities.ShouldReplaceTransparentPixels<TPixel>(this.transparentColorMode))
             {
                 clonedFrame = image.Frames.RootFrame.Clone();
-                EncodingUtilities.ClearTransparentPixels(clonedFrame, Color.Transparent);
+                EncodingUtilities.ReplaceTransparentPixels(clonedFrame, Color.Transparent);
             }
 
             ImageFrame<TPixel> encodingFrame = clonedFrame ?? image.Frames.RootFrame;
diff --git a/src/ImageSharp/Formats/Tiff/TiffEncoderCore.cs b/src/ImageSharp/Formats/Tiff/TiffEncoderCore.cs
index da55ef9f9b..1e12781a99 100644
--- a/src/ImageSharp/Formats/Tiff/TiffEncoderCore.cs
+++ b/src/ImageSharp/Formats/Tiff/TiffEncoderCore.cs
@@ -146,10 +146,10 @@ public void Encode<TPixel>(Image<TPixel> image, Stream stream, CancellationToken
             {
                 cancellationToken.ThrowIfCancellationRequested();
 
-                if (EncodingUtilities.ShouldClearTransparentPixels<TPixel>(this.transparentColorMode))
+                if (EncodingUtilities.ShouldReplaceTransparentPixels<TPixel>(this.transparentColorMode))
                 {
                     clonedFrame = frame.Clone();
-                    EncodingUtilities.ClearTransparentPixels(clonedFrame, Color.Transparent);
+                    EncodingUtilities.ReplaceTransparentPixels(clonedFrame, Color.Transparent);
                 }
 
                 ImageFrame<TPixel> encodingFrame = clonedFrame ?? frame;
diff --git a/src/ImageSharp/IndexedImageFrame{TPixel}.cs b/src/ImageSharp/IndexedImageFrame{TPixel}.cs
index 49c9e33eb1..a88cdb524e 100644
--- a/src/ImageSharp/IndexedImageFrame{TPixel}.cs
+++ b/src/ImageSharp/IndexedImageFrame{TPixel}.cs
@@ -25,7 +25,7 @@ public sealed class IndexedImageFrame<TPixel> : IPixelSource, IDisposable
     /// Initializes a new instance of the <see cref="IndexedImageFrame{TPixel}"/> class.
     /// </summary>
     /// <param name="configuration">
-    /// The configuration which allows altering default behaviour or extending the library.
+    /// The configuration which allows altering default behavior or extending the library.
     /// </param>
     /// <param name="width">The frame width.</param>
     /// <param name="height">The frame height.</param>
@@ -49,7 +49,7 @@ public IndexedImageFrame(Configuration configuration, int width, int height, Rea
     }
 
     /// <summary>
-    /// Gets the configuration which allows altering default behaviour or extending the library.
+    /// Gets the configuration which allows altering default behavior or extending the library.
     /// </summary>
     public Configuration Configuration { get; }
 
diff --git a/src/ImageSharp/Processing/Processors/Dithering/ErroDither.KnownTypes.cs b/src/ImageSharp/Processing/Processors/Dithering/ErrorDither.KnownTypes.cs
similarity index 100%
rename from src/ImageSharp/Processing/Processors/Dithering/ErroDither.KnownTypes.cs
rename to src/ImageSharp/Processing/Processors/Dithering/ErrorDither.KnownTypes.cs
diff --git a/src/ImageSharp/Processing/Processors/Dithering/PaletteDitherProcessor{TPixel}.cs b/src/ImageSharp/Processing/Processors/Dithering/PaletteDitherProcessor{TPixel}.cs
index 7e672393c7..bb9b4d8c8f 100644
--- a/src/ImageSharp/Processing/Processors/Dithering/PaletteDitherProcessor{TPixel}.cs
+++ b/src/ImageSharp/Processing/Processors/Dithering/PaletteDitherProcessor{TPixel}.cs
@@ -80,7 +80,7 @@ protected override void Dispose(bool disposing)
         Justification = "https://github.com/dotnet/roslyn-analyzers/issues/6151")]
     internal readonly struct DitherProcessor : IPaletteDitherImageProcessor<TPixel>, IDisposable
     {
-        private readonly EuclideanPixelMap<TPixel> pixelMap;
+        private readonly PixelMap<TPixel> pixelMap;
 
         [MethodImpl(InliningOptions.ShortMethod)]
         public DitherProcessor(
@@ -89,7 +89,7 @@ public DitherProcessor(
             float ditherScale)
         {
             this.Configuration = configuration;
-            this.pixelMap = new EuclideanPixelMap<TPixel>(configuration, palette);
+            this.pixelMap = PixelMapFactory.Create(configuration, palette, ColorMatchingMode.Hybrid);
             this.Palette = palette;
             this.DitherScale = ditherScale;
         }
diff --git a/src/ImageSharp/Processing/Processors/Quantization/ColorMatchingMode.cs b/src/ImageSharp/Processing/Processors/Quantization/ColorMatchingMode.cs
new file mode 100644
index 0000000000..26fd7d5d76
--- /dev/null
+++ b/src/ImageSharp/Processing/Processors/Quantization/ColorMatchingMode.cs
@@ -0,0 +1,28 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+namespace SixLabors.ImageSharp.Processing.Processors.Quantization;
+
+/// <summary>
+/// Defines the precision level used when matching colors during quantization.
+/// </summary>
+public enum ColorMatchingMode
+{
+    /// <summary>
+    /// Uses a coarse caching strategy optimized for performance at the expense of exact matches.
+    /// This provides the fastest matching but may yield approximate results.
+    /// </summary>
+    Coarse,
+
+    /// <summary>
+    /// Enables an exact color match cache for the first 512 unique colors encountered,
+    /// falling back to coarse matching thereafter.
+    /// </summary>
+    Hybrid,
+
+    /// <summary>
+    /// Performs exact color matching without any caching optimizations.
+    /// This is the slowest but most accurate matching strategy.
+    /// </summary>
+    Exact
+}
diff --git a/src/ImageSharp/Processing/Processors/Quantization/EuclideanPixelMap{TPixel,TCache}.cs b/src/ImageSharp/Processing/Processors/Quantization/EuclideanPixelMap{TPixel,TCache}.cs
new file mode 100644
index 0000000000..5b0c7252cb
--- /dev/null
+++ b/src/ImageSharp/Processing/Processors/Quantization/EuclideanPixelMap{TPixel,TCache}.cs
@@ -0,0 +1,184 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+using SixLabors.ImageSharp.PixelFormats;
+
+namespace SixLabors.ImageSharp.Processing.Processors.Quantization;
+
+/// <summary>
+/// Gets the closest color to the supplied color based upon the Euclidean distance.
+/// </summary>
+/// <typeparam name="TPixel">The pixel format.</typeparam>
+/// <typeparam name="TCache">The cache type.</typeparam>
+/// <para>
+/// This class is not thread safe and should not be accessed in parallel.
+/// Doing so will result in non-idempotent results.
+/// </para>
+internal sealed class EuclideanPixelMap<TPixel, TCache> : PixelMap<TPixel>
+    where TPixel : unmanaged, IPixel<TPixel>
+    where TCache : struct, IColorIndexCache<TCache>
+{
+    private Rgba32[] rgbaPalette;
+
+    // Do not make readonly. It's a mutable struct.
+#pragma warning disable IDE0044 // Add readonly modifier
+    private TCache cache;
+#pragma warning restore IDE0044 // Add readonly modifier
+
+    private readonly Configuration configuration;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="EuclideanPixelMap{TPixel, TCache}"/> class.
+    /// </summary>
+    /// <param name="configuration">Specifies the settings and resources for the pixel map's operations.</param>
+    /// <param name="palette">Defines the color palette used for pixel mapping.</param>
+    public EuclideanPixelMap(Configuration configuration, ReadOnlyMemory<TPixel> palette)
+    {
+        this.configuration = configuration;
+        this.Palette = palette;
+        this.rgbaPalette = new Rgba32[palette.Length];
+        this.cache = TCache.Create(configuration.MemoryAllocator);
+        PixelOperations<TPixel>.Instance.ToRgba32(configuration, this.Palette.Span, this.rgbaPalette);
+    }
+
+    /// <inheritdoc/>
+    [MethodImpl(InliningOptions.ShortMethod)]
+    public override int GetClosestColor(TPixel color, out TPixel match)
+    {
+        ref TPixel paletteRef = ref MemoryMarshal.GetReference(this.Palette.Span);
+        Rgba32 rgba = color.ToRgba32();
+
+        if (this.cache.TryGetValue(rgba, out short index))
+        {
+            match = Unsafe.Add(ref paletteRef, (ushort)index);
+            return index;
+        }
+
+        return this.GetClosestColorSlow(rgba, ref paletteRef, out match);
+    }
+
+    /// <inheritdoc/>
+    public override void Clear(ReadOnlyMemory<TPixel> palette)
+    {
+        this.Palette = palette;
+        this.rgbaPalette = new Rgba32[palette.Length];
+        PixelOperations<TPixel>.Instance.ToRgba32(this.configuration, this.Palette.Span, this.rgbaPalette);
+        this.cache.Clear();
+    }
+
+    [MethodImpl(InliningOptions.ColdPath)]
+    private int GetClosestColorSlow(Rgba32 rgba, ref TPixel paletteRef, out TPixel match)
+    {
+        // Loop through the palette and find the nearest match.
+        int index = 0;
+        float leastDistance = float.MaxValue;
+        for (int i = 0; i < this.rgbaPalette.Length; i++)
+        {
+            Rgba32 candidate = this.rgbaPalette[i];
+            if (candidate.PackedValue == rgba.PackedValue)
+            {
+                index = i;
+                break;
+            }
+
+            float distance = DistanceSquared(rgba, candidate);
+            if (distance == 0)
+            {
+                index = i;
+                break;
+            }
+
+            if (distance < leastDistance)
+            {
+                index = i;
+                leastDistance = distance;
+            }
+        }
+
+        // Now I have the index, pop it into the cache for next time
+        _ = this.cache.TryAdd(rgba, (short)index);
+        match = Unsafe.Add(ref paletteRef, (uint)index);
+
+        return index;
+    }
+
+    /// <summary>
+    /// Returns the Euclidean distance squared between two specified points.
+    /// </summary>
+    /// <param name="a">The first point.</param>
+    /// <param name="b">The second point.</param>
+    /// <returns>The distance squared.</returns>
+    [MethodImpl(InliningOptions.ShortMethod)]
+    private static float DistanceSquared(Rgba32 a, Rgba32 b)
+    {
+        float deltaR = a.R - b.R;
+        float deltaG = a.G - b.G;
+        float deltaB = a.B - b.B;
+        float deltaA = a.A - b.A;
+        return (deltaR * deltaR) + (deltaG * deltaG) + (deltaB * deltaB) + (deltaA * deltaA);
+    }
+
+    /// <inheritdoc/>
+    public override void Dispose() => this.cache.Dispose();
+}
+
+/// <summary>
+/// Represents a map of colors to indices.
+/// </summary>
+/// <typeparam name="TPixel">The pixel format.</typeparam>
+internal abstract class PixelMap<TPixel> : IDisposable
+    where TPixel : unmanaged, IPixel<TPixel>
+{
+    /// <summary>
+    /// Gets the color palette of this <see cref="PixelMap{TPixel}"/>.
+    /// </summary>
+    public ReadOnlyMemory<TPixel> Palette { get; private protected set; }
+
+    /// <summary>
+    /// Returns the closest color in the palette and the index of that pixel.
+    /// </summary>
+    /// <param name="color">The color to match.</param>
+    /// <param name="match">The matched color.</param>
+    /// <returns>
+    /// The <see cref="int"/> index.
+    /// </returns>
+    public abstract int GetClosestColor(TPixel color, out TPixel match);
+
+    /// <summary>
+    /// Clears the map, resetting it to use the given palette.
+    /// </summary>
+    /// <param name="palette">The color palette to map from.</param>
+    public abstract void Clear(ReadOnlyMemory<TPixel> palette);
+
+    /// <inheritdoc/>
+    public abstract void Dispose();
+}
+
+/// <summary>
+/// A factory for creating <see cref="PixelMap{TPixel}"/> instances.
+/// </summary>
+internal static class PixelMapFactory
+{
+    /// <summary>
+    /// Creates a new <see cref="PixelMap{TPixel}"/> instance.
+    /// </summary>
+    /// <typeparam name="TPixel">The pixel format.</typeparam>
+    /// <param name="configuration">The configuration.</param>
+    /// <param name="palette">The color palette to map from.</param>
+    /// <param name="colorMatchingMode">The color matching mode.</param>
+    /// <returns>
+    /// The <see cref="PixelMap{TPixel}"/>.
+    /// </returns>
+    public static PixelMap<TPixel> Create<TPixel>(
+        Configuration configuration,
+        ReadOnlyMemory<TPixel> palette,
+        ColorMatchingMode colorMatchingMode)
+        where TPixel : unmanaged, IPixel<TPixel> => colorMatchingMode switch
+        {
+            ColorMatchingMode.Hybrid => new EuclideanPixelMap<TPixel, HybridCache>(configuration, palette),
+            ColorMatchingMode.Exact => new EuclideanPixelMap<TPixel, NullCache>(configuration, palette),
+            _ => new EuclideanPixelMap<TPixel, CoarseCache>(configuration, palette),
+        };
+}
diff --git a/src/ImageSharp/Processing/Processors/Quantization/EuclideanPixelMap{TPixel}.cs b/src/ImageSharp/Processing/Processors/Quantization/EuclideanPixelMap{TPixel}.cs
deleted file mode 100644
index 250122e683..0000000000
--- a/src/ImageSharp/Processing/Processors/Quantization/EuclideanPixelMap{TPixel}.cs
+++ /dev/null
@@ -1,545 +0,0 @@
-// Copyright (c) Six Labors.
-// Licensed under the Six Labors Split License.
-
-using System.Buffers;
-using System.Numerics;
-using System.Runtime.CompilerServices;
-using System.Runtime.InteropServices;
-using SixLabors.ImageSharp.Memory;
-using SixLabors.ImageSharp.PixelFormats;
-
-namespace SixLabors.ImageSharp.Processing.Processors.Quantization;
-
-/// <summary>
-/// Gets the closest color to the supplied color based upon the Euclidean distance.
-/// </summary>
-/// <typeparam name="TPixel">The pixel format.</typeparam>
-/// <para>
-/// This class is not thread safe and should not be accessed in parallel.
-/// Doing so will result in non-idempotent results.
-/// </para>
-internal sealed class EuclideanPixelMap<TPixel> : IDisposable
-    where TPixel : unmanaged, IPixel<TPixel>
-{
-    private Rgba32[] rgbaPalette;
-    private readonly HybridColorDistanceCache cache;
-    private readonly Configuration configuration;
-
-    /// <summary>
-    /// Initializes a new instance of the <see cref="EuclideanPixelMap{TPixel}"/> class.
-    /// </summary>
-    /// <param name="configuration">The configuration.</param>
-    /// <param name="palette">The color palette to map from.</param>
-    public EuclideanPixelMap(Configuration configuration, ReadOnlyMemory<TPixel> palette)
-    {
-        this.configuration = configuration;
-        this.Palette = palette;
-        this.rgbaPalette = new Rgba32[palette.Length];
-        this.cache = new HybridColorDistanceCache(configuration.MemoryAllocator);
-        PixelOperations<TPixel>.Instance.ToRgba32(configuration, this.Palette.Span, this.rgbaPalette);
-    }
-
-    /// <summary>
-    /// Gets the color palette of this <see cref="EuclideanPixelMap{TPixel}"/>.
-    /// The palette memory is owned by the palette source that created it.
-    /// </summary>
-    public ReadOnlyMemory<TPixel> Palette { get; private set; }
-
-    /// <summary>
-    /// Returns the closest color in the palette and the index of that pixel.
-    /// The palette contents must match the one used in the constructor.
-    /// </summary>
-    /// <param name="color">The color to match.</param>
-    /// <param name="match">The matched color.</param>
-    /// <param name="transparencyThreshold">The transparency threshold.</param>
-    /// <returns>The <see cref="int"/> index.</returns>
-    [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public int GetClosestColor(TPixel color, out TPixel match, short transparencyThreshold = -1)
-    {
-        ref TPixel paletteRef = ref MemoryMarshal.GetReference(this.Palette.Span);
-        Rgba32 rgba = color.ToRgba32();
-
-        if (transparencyThreshold > -1 && rgba.A < transparencyThreshold)
-        {
-            rgba = default;
-        }
-
-        // Check if the color is in the lookup table
-        if (this.cache.TryGetValue(rgba, out short index))
-        {
-            match = Unsafe.Add(ref paletteRef, (ushort)index);
-            return index;
-        }
-
-        return this.GetClosestColorSlow(rgba, ref paletteRef, out match);
-    }
-
-    /// <summary>
-    /// Clears the map, resetting it to use the given palette.
-    /// </summary>
-    /// <param name="palette">The color palette to map from.</param>
-    public void Clear(ReadOnlyMemory<TPixel> palette)
-    {
-        this.Palette = palette;
-        this.rgbaPalette = new Rgba32[palette.Length];
-        PixelOperations<TPixel>.Instance.ToRgba32(this.configuration, this.Palette.Span, this.rgbaPalette);
-        this.cache.Clear();
-    }
-
-    [MethodImpl(MethodImplOptions.NoInlining)]
-    private int GetClosestColorSlow(Rgba32 rgba, ref TPixel paletteRef, out TPixel match)
-    {
-        // Loop through the palette and find the nearest match.
-        int index = 0;
-        float leastDistance = float.MaxValue;
-        for (int i = 0; i < this.rgbaPalette.Length; i++)
-        {
-            Rgba32 candidate = this.rgbaPalette[i];
-            if (candidate.PackedValue == rgba.PackedValue)
-            {
-                index = i;
-                break;
-            }
-
-            float distance = DistanceSquared(rgba, candidate);
-            if (distance == 0)
-            {
-                index = i;
-                break;
-            }
-
-            if (distance < leastDistance)
-            {
-                index = i;
-                leastDistance = distance;
-            }
-        }
-
-        // Now I have the index, pop it into the cache for next time
-        this.cache.Add(rgba, (short)index);
-        match = Unsafe.Add(ref paletteRef, (uint)index);
-
-        return index;
-    }
-
-    /// <summary>
-    /// Returns the Euclidean distance squared between two specified points.
-    /// </summary>
-    /// <param name="a">The first point.</param>
-    /// <param name="b">The second point.</param>
-    /// <returns>The distance squared.</returns>
-    [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    private static float DistanceSquared(Rgba32 a, Rgba32 b)
-    {
-        float deltaR = a.R - b.R;
-        float deltaG = a.G - b.G;
-        float deltaB = a.B - b.B;
-        float deltaA = a.A - b.A;
-        return (deltaR * deltaR) + (deltaG * deltaG) + (deltaB * deltaB) + (deltaA * deltaA);
-    }
-
-    public void Dispose() => this.cache.Dispose();
-
-    /// <summary>
-    /// A hybrid color distance cache that combines a small, fixed-capacity exact-match dictionary
-    /// (ExactCache, ~4–5 KB for up to 512 entries) with a coarse lookup table (CoarseCache) for 5,5,5,6 precision.
-    /// </summary>
-    /// <remarks>
-    /// ExactCache provides O(1) lookup for common cases using a simple 256-entry hash-based dictionary, while CoarseCache
-    /// quantizes RGB channels to 5 bits (yielding 32^3 buckets) and alpha to 6 bits, storing up to 4 alpha entries per bucket
-    /// (a design chosen based on probability theory to capture most real-world variations) for a total memory footprint of
-    /// roughly 576 KB. Lookups and insertions are performed in constant time, making the overall design both fast and memory-predictable.
-    /// </remarks>
-#pragma warning disable CA1001 // Types that own disposable fields should be disposable
-    // https://github.com/dotnet/roslyn-analyzers/issues/6151
-    private readonly unsafe struct HybridColorDistanceCache : IDisposable
-#pragma warning restore CA1001 // Types that own disposable fields should be disposable
-    {
-        private readonly CoarseCache coarseCache;
-        private readonly ExactCache exactCache;
-
-        public HybridColorDistanceCache(MemoryAllocator allocator)
-        {
-            this.exactCache = new ExactCache(allocator);
-            this.coarseCache = new CoarseCache(allocator);
-        }
-
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public readonly void Add(Rgba32 color, short index)
-        {
-            if (this.exactCache.TryAdd(color.PackedValue, index))
-            {
-                return;
-            }
-
-            this.coarseCache.Add(color, index);
-        }
-
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public readonly bool TryGetValue(Rgba32 color, out short match)
-        {
-            if (this.exactCache.TryGetValue(color.PackedValue, out match))
-            {
-                return true; // Exact match found
-            }
-
-            if (this.coarseCache.TryGetValue(color, out match))
-            {
-                return true; // Coarse match found
-            }
-
-            match = -1;
-            return false;
-        }
-
-        public readonly void Clear()
-        {
-            this.exactCache.Clear();
-            this.coarseCache.Clear();
-        }
-
-        public void Dispose()
-        {
-            this.exactCache.Dispose();
-            this.coarseCache.Dispose();
-        }
-    }
-
-    /// <summary>
-    /// A fixed-capacity dictionary with exactly 512 entries mapping a <see cref="uint"/> key
-    /// to a <see cref="short"/> value.
-    /// </summary>
-    /// <remarks>
-    /// The dictionary is implemented using a fixed array of 512 buckets and an entries array
-    /// of the same size. The bucket for a key is computed as (key &amp; 0x1FF), and collisions are
-    /// resolved through a linked chain stored in the <see cref="Entry.Next"/> field.
-    /// The overall memory usage is approximately 4–5 KB. Both lookup and insertion operations are,
-    /// on average, O(1) since the bucket is determined via a simple bitmask and collision chains are
-    /// typically very short; in the worst-case, the number of iterations is bounded by 256.
-    /// This guarantees highly efficient and predictable performance for small, fixed-size color palettes.
-    /// </remarks>
-    internal sealed unsafe class ExactCache : IDisposable
-    {
-        // Buckets array: each bucket holds the index (0-based) into the entries array
-        // of the first entry in the chain, or -1 if empty.
-        private readonly IMemoryOwner<short> bucketsOwner;
-        private MemoryHandle bucketsHandle;
-        private short* buckets;
-
-        // Entries array: stores up to 256 entries.
-        private readonly IMemoryOwner<Entry> entriesOwner;
-        private MemoryHandle entriesHandle;
-        private Entry* entries;
-
-        public const int Capacity = 512;
-
-        public ExactCache(MemoryAllocator allocator)
-        {
-            this.Count = 0;
-
-            // Allocate exactly 512 ints for buckets.
-            this.bucketsOwner = allocator.Allocate<short>(Capacity, AllocationOptions.Clean);
-            Span<short> bucketSpan = this.bucketsOwner.GetSpan();
-            bucketSpan.Fill(-1);
-            this.bucketsHandle = this.bucketsOwner.Memory.Pin();
-            this.buckets = (short*)this.bucketsHandle.Pointer;
-
-            // Allocate exactly 512 entries.
-            this.entriesOwner = allocator.Allocate<Entry>(Capacity, AllocationOptions.Clean);
-            this.entriesHandle = this.entriesOwner.Memory.Pin();
-            this.entries = (Entry*)this.entriesHandle.Pointer;
-        }
-
-        public int Count { get; private set; }
-
-        /// <summary>
-        /// Adds a key/value pair to the dictionary.
-        /// If the key already exists, the dictionary is left unchanged.
-        /// </summary>
-        /// <param name="key">The key to add.</param>
-        /// <param name="value">The value to add.</param>
-        /// <returns><see langword="true"/> if the key was added; otherwise, <see langword="false"/>.</returns>
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public bool TryAdd(uint key, short value)
-        {
-            if (this.Count == Capacity)
-            {
-                return false; // Dictionary is full.
-            }
-
-            // The key is a 32-bit unsigned integer representing an RGBA color, where the bytes are laid out as R|G|B|A
-            // (with R in the most significant byte and A in the least significant).
-            // To compute the bucket index:
-            // 1. (key >> 16) extracts the top 16 bits, effectively giving us the R and G channels.
-            // 2. (key >> 8) shifts the key right by 8 bits, bringing R, G, and B into the lower 24 bits (dropping A).
-            // 3. XORing these two values with the original key mixes bits from all four channels (R, G, B, and A),
-            //    which helps to counteract situations where one or more channels have a limited range.
-            // 4. Finally, we apply a bitmask of 0x1FF to keep only the lowest 9 bits, ensuring the result is between 0 and 511,
-            //    which corresponds to our fixed bucket count of 512.
-            int bucket = (int)(((key >> 16) ^ (key >> 8) ^ key) & 0x1FF);
-            int i = this.buckets[bucket];
-
-            // Traverse the collision chain.
-            Entry* entries = this.entries;
-            while (i != -1)
-            {
-                Entry e = entries[i];
-                if (e.Key == key)
-                {
-                    // Key already exists; do not overwrite.
-                    return false;
-                }
-
-                i = e.Next;
-            }
-
-            short index = (short)this.Count;
-            this.Count++;
-
-            // Insert the new entry:
-            entries[index].Key = key;
-            entries[index].Value = value;
-
-            // Link this new entry into the bucket chain.
-            entries[index].Next = this.buckets[bucket];
-            this.buckets[bucket] = index;
-            return true;
-        }
-
-        /// <summary>
-        /// Tries to retrieve the value associated with the specified key.
-        /// Returns true if the key is found; otherwise, returns false.
-        /// </summary>
-        /// <param name="key">The key to search for.</param>
-        /// <param name="value">The value associated with the key, if found.</param>
-        /// <returns><see langword="true"/> if the key is found; otherwise, <see langword="false"/>.</returns>
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public bool TryGetValue(uint key, out short value)
-        {
-            int bucket = (int)(((key >> 16) ^ (key >> 8) ^ key) & 0x1FF);
-            int i = this.buckets[bucket];
-
-            // If the bucket is empty, return immediately.
-            if (i == -1)
-            {
-                value = -1;
-                return false;
-            }
-
-            // Traverse the chain.
-            Entry* entries = this.entries;
-            do
-            {
-                Entry e = entries[i];
-                if (e.Key == key)
-                {
-                    value = e.Value;
-                    return true;
-                }
-
-                i = e.Next;
-            }
-            while (i != -1);
-
-            value = -1;
-            return false;
-        }
-
-        /// <summary>
-        /// Clears the dictionary.
-        /// </summary>
-        public void Clear()
-        {
-            Span<short> bucketSpan = this.bucketsOwner.GetSpan();
-            bucketSpan.Fill(-1);
-            this.Count = 0;
-        }
-
-        public void Dispose()
-        {
-            this.bucketsHandle.Dispose();
-            this.bucketsOwner.Dispose();
-            this.entriesHandle.Dispose();
-            this.entriesOwner.Dispose();
-            this.buckets = null;
-            this.entries = null;
-        }
-
-        private struct Entry
-        {
-            public uint Key;     // The key (packed RGBA)
-            public short Value;  // The value; -1 means unused.
-            public short Next;     // Index of the next entry in the chain, or -1 if none.
-        }
-    }
-
-    /// <summary>
-    /// <para>
-    /// CoarseCache is a fast, low-memory lookup structure for caching palette indices associated with RGBA values,
-    /// using a quantized representation of 5,5,5,6 (RGB: 5 bits each, Alpha: 6 bits).
-    /// </para>
-    /// <para>
-    /// The cache quantizes the RGB channels to 5 bits each, resulting in 32 levels per channel and a total of 32³ = 32,768 buckets.
-    /// Each bucket is represented by an <see cref="AlphaBucket"/>, which holds a small, inline array of alpha entries.
-    /// Each alpha entry stores the alpha value quantized to 6 bits (0–63) along with a palette index (a 16-bit value).
-    /// </para>
-    /// <para>
-    /// Performance Characteristics:
-    ///   - Lookup: O(1) for computing the bucket index from the RGB channels, plus a small constant time (up to 4 iterations)
-    ///     to search through the alpha entries in the bucket.
-    ///   - Insertion: O(1) for bucket index computation and a quick linear search over a very small (fixed) number of entries.
-    /// </para>
-    /// <para>
-    /// Memory Characteristics:
-    ///   - The cache consists of 32,768 buckets.
-    ///   - Each <see cref="AlphaBucket"/> is implemented using an inline array with a capacity of 4 entries.
-    ///   - Each bucket occupies approximately 18 bytes.
-    ///   - Overall, the buckets occupy roughly 32,768 × 18 = 589,824 bytes (576 KB).
-    /// </para>
-    /// <para>
-    /// This design provides nearly constant-time lookup and insertion with minimal memory usage,
-    /// making it ideal for applications such as color distance caching in images with a limited palette (up to 256 entries).
-    /// </para>
-    /// </summary>
-    internal sealed unsafe class CoarseCache : IDisposable
-    {
-        // Use 5 bits per channel for R, G, and B: 32 levels each.
-        // Total buckets = 32^3 = 32768.
-        private const int RgbBits = 5;
-        private const int BucketCount = 1 << (RgbBits * 3); // 32768
-        private readonly IMemoryOwner<AlphaBucket> bucketsOwner;
-        private readonly AlphaBucket* buckets;
-        private MemoryHandle bucketHandle;
-
-        public CoarseCache(MemoryAllocator allocator)
-        {
-            this.bucketsOwner = allocator.Allocate<AlphaBucket>(BucketCount, AllocationOptions.Clean);
-            this.bucketHandle = this.bucketsOwner.Memory.Pin();
-            this.buckets = (AlphaBucket*)this.bucketHandle.Pointer;
-        }
-
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static int GetBucketIndex(byte r, byte g, byte b)
-        {
-            int qr = r >> (8 - RgbBits);
-            int qg = g >> (8 - RgbBits);
-            int qb = b >> (8 - RgbBits);
-
-            // Combine the quantized channels into a single index.
-            return (qr << (RgbBits * 2)) | (qg << RgbBits) | qb;
-        }
-
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static byte QuantizeAlpha(byte a)
-
-            // Quantize to 6 bits: shift right by (8 - 6) = 2 bits.
-            => (byte)(a >> 2);
-
-        public void Add(Rgba32 color, short paletteIndex)
-        {
-            int bucketIndex = GetBucketIndex(color.R, color.G, color.B);
-            byte quantAlpha = QuantizeAlpha(color.A);
-            this.buckets[bucketIndex].Add(quantAlpha, paletteIndex);
-        }
-
-        public void Dispose()
-        {
-            this.bucketHandle.Dispose();
-            this.bucketsOwner.Dispose();
-        }
-
-        public bool TryGetValue(Rgba32 color, out short paletteIndex)
-        {
-            int bucketIndex = GetBucketIndex(color.R, color.G, color.B);
-            byte quantAlpha = QuantizeAlpha(color.A);
-            return this.buckets[bucketIndex].TryGetValue(quantAlpha, out paletteIndex);
-        }
-
-        public void Clear()
-        {
-            Span<AlphaBucket> bucketsSpan = this.bucketsOwner.GetSpan();
-            bucketsSpan.Clear();
-        }
-
-        public struct AlphaEntry
-        {
-            // Store the alpha value quantized to 6 bits (0..63)
-            public byte QuantizedAlpha;
-            public short PaletteIndex;
-        }
-
-        public struct AlphaBucket
-        {
-            // Fixed capacity for alpha entries in this bucket.
-            // We choose a capacity of 4 for several reasons:
-            //
-            // 1. The alpha channel is quantized to 6 bits, so there are 64 possible distinct values.
-            //    In the worst-case, a given RGB bucket might encounter up to 64 different alpha values.
-            //
-            // 2. However, in practice (based on probability theory and typical image data),
-            //    the number of unique alpha values that actually occur for a given quantized RGB
-            //    bucket is usually very small. If you randomly sample 4 values out of 64,
-            //    the probability that these 4 samples are all unique is high if the distribution
-            //    of alpha values is skewed or if only a few alpha values are used.
-            //
-            // 3. Statistically, for many real-world images, most RGB buckets will have only a couple
-            //    of unique alpha values. Allocating 4 slots per bucket provides a good trade-off:
-            //    it captures the common-case scenario while keeping overall memory usage low.
-            //
-            // 4. Even if more than 4 unique alpha values occur in a bucket,
-            //    our design overwrites the first entry. This behavior gives us some "wriggle room"
-            //    while preserving the most frequently encountered or most recent values.
-            public const int Capacity = 4;
-            public byte Count;
-            private InlineArray4<AlphaEntry> entries;
-
-            [MethodImpl(MethodImplOptions.AggressiveInlining)]
-            public bool TryGetValue(byte quantizedAlpha, out short paletteIndex)
-            {
-                for (int i = 0; i < this.Count; i++)
-                {
-                    ref AlphaEntry entry = ref this.entries[i];
-                    if (entry.QuantizedAlpha == quantizedAlpha)
-                    {
-                        paletteIndex = entry.PaletteIndex;
-                        return true;
-                    }
-                }
-
-                paletteIndex = -1;
-                return false;
-            }
-
-            [MethodImpl(MethodImplOptions.AggressiveInlining)]
-            public void Add(byte quantizedAlpha, short paletteIndex)
-            {
-                // Check for an existing entry with the same quantized alpha.
-                for (int i = 0; i < this.Count; i++)
-                {
-                    ref AlphaEntry entry = ref this.entries[i];
-                    if (entry.QuantizedAlpha == quantizedAlpha)
-                    {
-                        // Update palette index if found.
-                        entry.PaletteIndex = paletteIndex;
-                        return;
-                    }
-                }
-
-                // If there's room, add a new entry.
-                if (this.Count < Capacity)
-                {
-                    ref AlphaEntry newEntry = ref this.entries[this.Count];
-                    newEntry.QuantizedAlpha = quantizedAlpha;
-                    newEntry.PaletteIndex = paletteIndex;
-                    this.Count++;
-                }
-                else
-                {
-                    // Bucket is full. Overwrite the first entry to give us some wriggle room.
-                    this.entries[0].QuantizedAlpha = quantizedAlpha;
-                    this.entries[0].PaletteIndex = paletteIndex;
-                }
-            }
-        }
-    }
-}
diff --git a/src/ImageSharp/Processing/Processors/Quantization/IColorIndexCache.cs b/src/ImageSharp/Processing/Processors/Quantization/IColorIndexCache.cs
new file mode 100644
index 0000000000..52efc62b7e
--- /dev/null
+++ b/src/ImageSharp/Processing/Processors/Quantization/IColorIndexCache.cs
@@ -0,0 +1,491 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Buffers;
+using System.Runtime.CompilerServices;
+using SixLabors.ImageSharp.Memory;
+using SixLabors.ImageSharp.PixelFormats;
+
+namespace SixLabors.ImageSharp.Processing.Processors.Quantization;
+
+/// <summary>
+/// Represents a cache used for efficiently retrieving palette indices for colors.
+/// </summary>
+internal interface IColorIndexCache : IDisposable
+{
+    /// <summary>
+    /// Adds a color to the cache.
+    /// </summary>
+    /// <param name="color">The color to add.</param>
+    /// <param name="value">The index of the color in the palette.</param>
+    /// <returns>
+    /// <see langword="true"/> if the color was added; otherwise, <see langword="false"/>.
+    /// </returns>
+    public bool TryAdd(Rgba32 color, short value);
+
+    /// <summary>
+    /// Gets the index of the color in the palette.
+    /// </summary>
+    /// <param name="color">The color to get the index for.</param>
+    /// <param name="value">The index of the color in the palette.</param>
+    /// <returns>
+    /// <see langword="true"/> if the color is in the palette; otherwise, <see langword="false"/>.
+    /// </returns>
+    public bool TryGetValue(Rgba32 color, out short value);
+
+    /// <summary>
+    /// Clears the cache.
+    /// </summary>
+    public void Clear();
+}
+
+/// <summary>
+/// Represents a cache used for efficiently retrieving palette indices for colors.
+/// </summary>
+/// <typeparam name="T">The type of the cache.</typeparam>
+internal interface IColorIndexCache<T> : IColorIndexCache
+   where T : struct, IColorIndexCache
+{
+    /// <summary>
+    /// Creates a new instance of the cache.
+    /// </summary>
+    /// <param name="allocator">The memory allocator to use.</param>
+    /// <returns>
+    /// The new instance of the cache.
+    /// </returns>
+    public static abstract T Create(MemoryAllocator allocator);
+}
+
+/// <summary>
+/// A hybrid color distance cache that combines a small, fixed-capacity exact-match dictionary
+/// (ExactCache, ~4–5 KB for up to 512 entries) with a coarse lookup table (CoarseCache) for 5,5,5,6 precision.
+/// </summary>
+/// <remarks>
+/// ExactCache provides O(1) lookup for common cases using a simple 256-entry hash-based dictionary, while CoarseCache
+/// quantizes RGB channels to 5 bits (yielding 32^3 buckets) and alpha to 6 bits, storing up to 4 alpha entries per bucket
+/// (a design chosen based on probability theory to capture most real-world variations) for a total memory footprint of
+/// roughly 576 KB. Lookups and insertions are performed in constant time, making the overall design both fast and memory-predictable.
+/// </remarks>
+internal unsafe struct HybridCache : IColorIndexCache<HybridCache>
+{
+    private CoarseCache coarseCache;
+    private ExactCache exactCache;
+
+    public HybridCache(MemoryAllocator allocator)
+    {
+        this.exactCache = ExactCache.Create(allocator);
+        this.coarseCache = CoarseCache.Create(allocator);
+    }
+
+    /// <inheritdoc/>
+    public static HybridCache Create(MemoryAllocator allocator) => new(allocator);
+
+    /// <inheritdoc/>
+    [MethodImpl(InliningOptions.ShortMethod)]
+    public bool TryAdd(Rgba32 color, short index)
+    {
+        if (this.exactCache.TryAdd(color, index))
+        {
+            return true;
+        }
+
+        return this.coarseCache.TryAdd(color, index);
+    }
+
+    /// <inheritdoc/>
+    [MethodImpl(InliningOptions.ShortMethod)]
+    public readonly bool TryGetValue(Rgba32 color, out short value)
+    {
+        if (this.exactCache.TryGetValue(color, out value))
+        {
+            return true;
+        }
+
+        return this.coarseCache.TryGetValue(color, out value);
+    }
+
+    /// <inheritdoc/>
+    public readonly void Clear()
+    {
+        this.exactCache.Clear();
+        this.coarseCache.Clear();
+    }
+
+    /// <inheritdoc/>
+    public void Dispose()
+    {
+        this.exactCache.Dispose();
+        this.coarseCache.Dispose();
+    }
+}
+
+/// <summary>
+/// <para>
+/// CoarseCache is a fast, low-memory lookup structure for caching palette indices associated with RGBA values,
+/// using a quantized representation of 5,5,5,6 (RGB: 5 bits each, Alpha: 6 bits).
+/// </para>
+/// <para>
+/// The cache quantizes the RGB channels to 5 bits each, resulting in 32 levels per channel and a total of 32³ = 32,768 buckets.
+/// Each bucket is represented by an <see cref="AlphaBucket"/>, which holds a small, inline array of alpha entries.
+/// Each alpha entry stores the alpha value quantized to 6 bits (0–63) along with a palette index (a 16-bit value).
+/// </para>
+/// <para>
+/// Performance Characteristics:
+///   - Lookup: O(1) for computing the bucket index from the RGB channels, plus a small constant time (up to 4 iterations)
+///     to search through the alpha entries in the bucket.
+///   - Insertion: O(1) for bucket index computation and a quick linear search over a very small (fixed) number of entries.
+/// </para>
+/// <para>
+/// Memory Characteristics:
+///   - The cache consists of 32,768 buckets.
+///   - Each <see cref="AlphaBucket"/> is implemented using an inline array with a capacity of 4 entries.
+///   - Each bucket occupies approximately 18 bytes.
+///   - Overall, the buckets occupy roughly 32,768 × 18 = 589,824 bytes (576 KB).
+/// </para>
+/// <para>
+/// This design provides nearly constant-time lookup and insertion with minimal memory usage,
+/// making it ideal for applications such as color distance caching in images with a limited palette (up to 256 entries).
+/// </para>
+/// </summary>
+internal unsafe struct CoarseCache : IColorIndexCache<CoarseCache>
+{
+    // Use 5 bits per channel for R, G, and B: 32 levels each.
+    // Total buckets = 32^3 = 32768.
+    private const int RgbBits = 5;
+    private const int RgbShift = 8 - RgbBits; // 3
+    private const int BucketCount = 1 << (RgbBits * 3); // 32768
+    private readonly IMemoryOwner<AlphaBucket> bucketsOwner;
+    private readonly AlphaBucket* buckets;
+    private MemoryHandle bucketHandle;
+
+    private CoarseCache(MemoryAllocator allocator)
+    {
+        this.bucketsOwner = allocator.Allocate<AlphaBucket>(BucketCount, AllocationOptions.Clean);
+        this.bucketHandle = this.bucketsOwner.Memory.Pin();
+        this.buckets = (AlphaBucket*)this.bucketHandle.Pointer;
+    }
+
+    /// <inheritdoc/>
+    public static CoarseCache Create(MemoryAllocator allocator) => new(allocator);
+
+    /// <inheritdoc/>
+    public readonly bool TryAdd(Rgba32 color, short paletteIndex)
+    {
+        int bucketIndex = GetBucketIndex(color.R, color.G, color.B);
+        byte quantAlpha = QuantizeAlpha(color.A);
+        this.buckets[bucketIndex].Add(quantAlpha, paletteIndex);
+        return true;
+    }
+
+    /// <inheritdoc/>
+    public readonly bool TryGetValue(Rgba32 color, out short paletteIndex)
+    {
+        int bucketIndex = GetBucketIndex(color.R, color.G, color.B);
+        byte quantAlpha = QuantizeAlpha(color.A);
+        return this.buckets[bucketIndex].TryGetValue(quantAlpha, out paletteIndex);
+    }
+
+    /// <inheritdoc/>
+    public readonly void Clear()
+    {
+        Span<AlphaBucket> bucketsSpan = this.bucketsOwner.GetSpan();
+        bucketsSpan.Clear();
+    }
+
+    /// <inheritdoc/>
+    public void Dispose()
+    {
+        this.bucketHandle.Dispose();
+        this.bucketsOwner.Dispose();
+    }
+
+    [MethodImpl(InliningOptions.ShortMethod)]
+    private static int GetBucketIndex(byte r, byte g, byte b)
+    {
+        int qr = r >> RgbShift;
+        int qg = g >> RgbShift;
+        int qb = b >> RgbShift;
+
+        // Combine the quantized channels into a single index.
+        return (qr << (RgbBits << 1)) | (qg << RgbBits) | qb;
+    }
+
+    [MethodImpl(InliningOptions.ShortMethod)]
+    private static byte QuantizeAlpha(byte a)
+
+        // Quantize to 6 bits: shift right by (8 - 6) = 2 bits.
+        => (byte)(a >> 2);
+
+    public struct AlphaEntry
+    {
+        // Store the alpha value quantized to 6 bits (0..63)
+        public byte QuantizedAlpha;
+        public short PaletteIndex;
+    }
+
+    public struct AlphaBucket
+    {
+        // Fixed capacity for alpha entries in this bucket.
+        // We choose a capacity of 4 for several reasons:
+        //
+        // 1. The alpha channel is quantized to 6 bits, so there are 64 possible distinct values.
+        //    In the worst-case, a given RGB bucket might encounter up to 64 different alpha values.
+        //
+        // 2. However, in practice (based on probability theory and typical image data),
+        //    the number of unique alpha values that actually occur for a given quantized RGB
+        //    bucket is usually very small. If you randomly sample 4 values out of 64,
+        //    the probability that these 4 samples are all unique is high if the distribution
+        //    of alpha values is skewed or if only a few alpha values are used.
+        //
+        // 3. Statistically, for many real-world images, most RGB buckets will have only a couple
+        //    of unique alpha values. Allocating 4 slots per bucket provides a good trade-off:
+        //    it captures the common-case scenario while keeping overall memory usage low.
+        //
+        // 4. Even if more than 4 unique alpha values occur in a bucket,
+        //    our design overwrites the first entry. This behavior gives us some "wriggle room"
+        //    while preserving the most frequently encountered or most recent values.
+        public const int Capacity = 4;
+        public byte Count;
+        private InlineArray4<AlphaEntry> entries;
+
+        [MethodImpl(InliningOptions.ShortMethod)]
+        public bool TryGetValue(byte quantizedAlpha, out short paletteIndex)
+        {
+            for (int i = 0; i < this.Count; i++)
+            {
+                ref AlphaEntry entry = ref this.entries[i];
+                if (entry.QuantizedAlpha == quantizedAlpha)
+                {
+                    paletteIndex = entry.PaletteIndex;
+                    return true;
+                }
+            }
+
+            paletteIndex = -1;
+            return false;
+        }
+
+        [MethodImpl(InliningOptions.ShortMethod)]
+        public void Add(byte quantizedAlpha, short paletteIndex)
+        {
+            // Check for an existing entry with the same quantized alpha.
+            for (int i = 0; i < this.Count; i++)
+            {
+                ref AlphaEntry entry = ref this.entries[i];
+                if (entry.QuantizedAlpha == quantizedAlpha)
+                {
+                    // Update palette index if found.
+                    entry.PaletteIndex = paletteIndex;
+                    return;
+                }
+            }
+
+            // If there's room, add a new entry.
+            if (this.Count < Capacity)
+            {
+                ref AlphaEntry newEntry = ref this.entries[this.Count];
+                newEntry.QuantizedAlpha = quantizedAlpha;
+                newEntry.PaletteIndex = paletteIndex;
+                this.Count++;
+            }
+            else
+            {
+                // Bucket is full. Overwrite the first entry to give us some wriggle room.
+                this.entries[0].QuantizedAlpha = quantizedAlpha;
+                this.entries[0].PaletteIndex = paletteIndex;
+            }
+        }
+    }
+}
+
+/// <summary>
+/// A fixed-capacity dictionary with exactly 512 entries mapping a <see cref="uint"/> key
+/// to a <see cref="short"/> value.
+/// </summary>
+/// <remarks>
+/// The dictionary is implemented using a fixed array of 512 buckets and an entries array
+/// of the same size. The bucket for a key is computed as (key &amp; 0x1FF), and collisions are
+/// resolved through a linked chain stored in the <see cref="Entry.Next"/> field.
+/// The overall memory usage is approximately 4–5 KB. Both lookup and insertion operations are,
+/// on average, O(1) since the bucket is determined via a simple bitmask and collision chains are
+/// typically very short; in the worst-case, the number of iterations is bounded by 256.
+/// This guarantees highly efficient and predictable performance for small, fixed-size color palettes.
+/// </remarks>
+internal unsafe struct ExactCache : IColorIndexCache<ExactCache>
+{
+    // Buckets array: each bucket holds the index (0-based) into the entries array
+    // of the first entry in the chain, or -1 if empty.
+    private readonly IMemoryOwner<short> bucketsOwner;
+    private MemoryHandle bucketsHandle;
+    private short* buckets;
+
+    // Entries array: stores up to 256 entries.
+    private readonly IMemoryOwner<Entry> entriesOwner;
+    private MemoryHandle entriesHandle;
+    private Entry* entries;
+
+    public const int Capacity = 512;
+
+    private ExactCache(MemoryAllocator allocator)
+    {
+        this.Count = 0;
+
+        // Allocate exactly 512 indexes for buckets.
+        this.bucketsOwner = allocator.Allocate<short>(Capacity, AllocationOptions.Clean);
+        Span<short> bucketSpan = this.bucketsOwner.GetSpan();
+        bucketSpan.Fill(-1);
+        this.bucketsHandle = this.bucketsOwner.Memory.Pin();
+        this.buckets = (short*)this.bucketsHandle.Pointer;
+
+        // Allocate exactly 512 entries.
+        this.entriesOwner = allocator.Allocate<Entry>(Capacity, AllocationOptions.Clean);
+        this.entriesHandle = this.entriesOwner.Memory.Pin();
+        this.entries = (Entry*)this.entriesHandle.Pointer;
+    }
+
+    public int Count { get; private set; }
+
+    /// <inheritdoc/>
+    public static ExactCache Create(MemoryAllocator allocator) => new(allocator);
+
+    /// <inheritdoc/>
+    [MethodImpl(InliningOptions.ShortMethod)]
+    public bool TryAdd(Rgba32 color, short value)
+    {
+        if (this.Count == Capacity)
+        {
+            return false; // Dictionary is full.
+        }
+
+        uint key = color.PackedValue;
+
+        // The key is a 32-bit unsigned integer representing an RGBA color, where the bytes are laid out as R|G|B|A
+        // (with R in the most significant byte and A in the least significant).
+        // To compute the bucket index:
+        // 1. (key >> 16) extracts the top 16 bits, effectively giving us the R and G channels.
+        // 2. (key >> 8) shifts the key right by 8 bits, bringing R, G, and B into the lower 24 bits (dropping A).
+        // 3. XORing these two values with the original key mixes bits from all four channels (R, G, B, and A),
+        //    which helps to counteract situations where one or more channels have a limited range.
+        // 4. Finally, we apply a bitmask of 0x1FF to keep only the lowest 9 bits, ensuring the result is between 0 and 511,
+        //    which corresponds to our fixed bucket count of 512.
+        int bucket = (int)(((key >> 16) ^ (key >> 8) ^ key) & 0x1FF);
+        int i = this.buckets[bucket];
+
+        // Traverse the collision chain.
+        Entry* entries = this.entries;
+        while (i != -1)
+        {
+            Entry e = entries[i];
+            if (e.Key == key)
+            {
+                // Key already exists; do not overwrite.
+                return false;
+            }
+
+            i = e.Next;
+        }
+
+        short index = (short)this.Count;
+        this.Count++;
+
+        // Insert the new entry:
+        entries[index].Key = key;
+        entries[index].Value = value;
+
+        // Link this new entry into the bucket chain.
+        entries[index].Next = this.buckets[bucket];
+        this.buckets[bucket] = index;
+        return true;
+    }
+
+    /// <inheritdoc/>
+    [MethodImpl(InliningOptions.ShortMethod)]
+    public bool TryGetValue(Rgba32 color, out short value)
+    {
+        uint key = color.PackedValue;
+        int bucket = (int)(((key >> 16) ^ (key >> 8) ^ key) & 0x1FF);
+        int i = this.buckets[bucket];
+
+        // If the bucket is empty, return immediately.
+        if (i == -1)
+        {
+            value = -1;
+            return false;
+        }
+
+        // Traverse the chain.
+        Entry* entries = this.entries;
+        do
+        {
+            Entry e = entries[i];
+            if (e.Key == key)
+            {
+                value = e.Value;
+                return true;
+            }
+
+            i = e.Next;
+        }
+        while (i != -1);
+
+        value = -1;
+        return false;
+    }
+
+    /// <summary>
+    /// Clears the dictionary.
+    /// </summary>
+    public void Clear()
+    {
+        Span<short> bucketSpan = this.bucketsOwner.GetSpan();
+        bucketSpan.Fill(-1);
+        this.Count = 0;
+    }
+
+    public void Dispose()
+    {
+        this.bucketsHandle.Dispose();
+        this.bucketsOwner.Dispose();
+        this.entriesHandle.Dispose();
+        this.entriesOwner.Dispose();
+        this.buckets = null;
+        this.entries = null;
+    }
+
+    private struct Entry
+    {
+        public uint Key;     // The key (packed RGBA)
+        public short Value;  // The value; -1 means unused.
+        public short Next;     // Index of the next entry in the chain, or -1 if none.
+    }
+}
+
+/// <summary>
+/// Represents a cache that does not store any values.
+/// It allows adding colors, but always returns false when trying to retrieve them.
+/// </summary>
+internal readonly struct NullCache : IColorIndexCache<NullCache>
+{
+    /// <inheritdoc/>
+    public static NullCache Create(MemoryAllocator allocator) => default;
+
+    /// <inheritdoc/>
+    public bool TryAdd(Rgba32 color, short value) => true;
+
+    /// <inheritdoc/>
+    public bool TryGetValue(Rgba32 color, out short value)
+    {
+        value = -1;
+        return false;
+    }
+
+    /// <inheritdoc/>
+    public void Clear()
+    {
+    }
+
+    /// <inheritdoc/>
+    public void Dispose()
+    {
+    }
+}
diff --git a/src/ImageSharp/Processing/Processors/Quantization/IQuantizer.cs b/src/ImageSharp/Processing/Processors/Quantization/IQuantizer.cs
index 9d5b606040..02dce8ca48 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/IQuantizer.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/IQuantizer.cs
@@ -13,7 +13,7 @@ public interface IQuantizer
     /// <summary>
     /// Gets the quantizer options defining quantization rules.
     /// </summary>
-    QuantizerOptions Options { get; }
+    public QuantizerOptions Options { get; }
 
     /// <summary>
     /// Creates the generic frame quantizer.
@@ -21,7 +21,7 @@ public interface IQuantizer
     /// <param name="configuration">The <see cref="Configuration"/> to configure internal operations.</param>
     /// <typeparam name="TPixel">The pixel format.</typeparam>
     /// <returns>The <see cref="IQuantizer{TPixel}"/>.</returns>
-    IQuantizer<TPixel> CreatePixelSpecificQuantizer<TPixel>(Configuration configuration)
+    public IQuantizer<TPixel> CreatePixelSpecificQuantizer<TPixel>(Configuration configuration)
         where TPixel : unmanaged, IPixel<TPixel>;
 
     /// <summary>
@@ -31,6 +31,6 @@ IQuantizer<TPixel> CreatePixelSpecificQuantizer<TPixel>(Configuration configurat
     /// <param name="configuration">The <see cref="Configuration"/> to configure internal operations.</param>
     /// <param name="options">The options to create the quantizer with.</param>
     /// <returns>The <see cref="IQuantizer{TPixel}"/>.</returns>
-    IQuantizer<TPixel> CreatePixelSpecificQuantizer<TPixel>(Configuration configuration, QuantizerOptions options)
+    public IQuantizer<TPixel> CreatePixelSpecificQuantizer<TPixel>(Configuration configuration, QuantizerOptions options)
         where TPixel : unmanaged, IPixel<TPixel>;
 }
diff --git a/src/ImageSharp/Processing/Processors/Quantization/IQuantizer{TPixel}.cs b/src/ImageSharp/Processing/Processors/Quantization/IQuantizer{TPixel}.cs
index dc5bdbd627..02c2052fef 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/IQuantizer{TPixel}.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/IQuantizer{TPixel}.cs
@@ -1,6 +1,7 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
+using SixLabors.ImageSharp.Formats;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;
 
@@ -27,7 +28,7 @@ public interface IQuantizer<TPixel> : IDisposable
     /// Gets the quantized color palette.
     /// </summary>
     /// <exception cref="InvalidOperationException">
-    /// The palette has not been built via <see cref="AddPaletteColors"/>.
+    /// The palette has not been built via <see cref="AddPaletteColors(in Buffer2DRegion{TPixel})"/>.
     /// </exception>
     public ReadOnlyMemory<TPixel> Palette { get; }
 
@@ -35,21 +36,45 @@ public interface IQuantizer<TPixel> : IDisposable
     /// Adds colors to the quantized palette from the given pixel source.
     /// </summary>
     /// <param name="pixelRegion">The <see cref="Buffer2DRegion{T}"/> of source pixels to register.</param>
-    public void AddPaletteColors(in Buffer2DRegion<TPixel> pixelRegion);
+    public void AddPaletteColors(in Buffer2DRegion<TPixel> pixelRegion)
+        => this.AddPaletteColors(pixelRegion, TransparentColorMode.Preserve);
+
+    /// <summary>
+    /// Adds colors to the quantized palette from the given pixel source.
+    /// </summary>
+    /// <param name="pixelRegion">The <see cref="Buffer2DRegion{T}"/> of source pixels to register.</param>
+    /// <param name="mode">The <see cref="TransparentColorMode"/> to use when adding colors to the palette.</param>
+    public void AddPaletteColors(in Buffer2DRegion<TPixel> pixelRegion, TransparentColorMode mode);
+
+    /// <summary>
+    /// Quantizes an image frame and return the resulting output pixels.
+    /// </summary>
+    /// <param name="source">The source image frame to quantize.</param>
+    /// <param name="bounds">The bounds within the frame to quantize.</param>
+    /// <returns>
+    /// A <see cref="IndexedImageFrame{TPixel}"/> representing a quantized version of the source frame pixels.
+    /// </returns>
+    /// <remarks>
+    /// Only executes the second (quantization) step. The palette has to be built by calling <see cref="AddPaletteColors(in Buffer2DRegion{TPixel})"/>.
+    /// To run both steps, use <see cref="QuantizerUtilities.BuildPaletteAndQuantizeFrame{TPixel}(IQuantizer{TPixel}, ImageFrame{TPixel}, Rectangle)"/>.
+    /// </remarks>
+    public IndexedImageFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> source, Rectangle bounds)
+        => this.QuantizeFrame(source, bounds, TransparentColorMode.Preserve);
 
     /// <summary>
     /// Quantizes an image frame and return the resulting output pixels.
     /// </summary>
     /// <param name="source">The source image frame to quantize.</param>
     /// <param name="bounds">The bounds within the frame to quantize.</param>
+    /// <param name="mode">The <see cref="TransparentColorMode"/> to use when quantizing the frame.</param>
     /// <returns>
     /// A <see cref="IndexedImageFrame{TPixel}"/> representing a quantized version of the source frame pixels.
     /// </returns>
     /// <remarks>
-    /// Only executes the second (quantization) step. The palette has to be built by calling <see cref="AddPaletteColors"/>.
-    /// To run both steps, use <see cref="QuantizerUtilities.BuildPaletteAndQuantizeFrame{TPixel}"/>.
+    /// Only executes the second (quantization) step. The palette has to be built by calling <see cref="AddPaletteColors(in Buffer2DRegion{TPixel})"/>.
+    /// To run both steps, use <see cref="QuantizerUtilities.BuildPaletteAndQuantizeFrame{TPixel}(IQuantizer{TPixel}, ImageFrame{TPixel}, Rectangle)"/>.
     /// </remarks>
-    public IndexedImageFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> source, Rectangle bounds);
+    public IndexedImageFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> source, Rectangle bounds, TransparentColorMode mode);
 
     /// <summary>
     /// Returns the index and color from the quantized palette corresponding to the given color.
diff --git a/src/ImageSharp/Processing/Processors/Quantization/IQuantizingPixelRowDelegate{TPixel}.cs b/src/ImageSharp/Processing/Processors/Quantization/IQuantizingPixelRowDelegate{TPixel}.cs
new file mode 100644
index 0000000000..ce06adf455
--- /dev/null
+++ b/src/ImageSharp/Processing/Processors/Quantization/IQuantizingPixelRowDelegate{TPixel}.cs
@@ -0,0 +1,27 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using SixLabors.ImageSharp.Formats;
+using SixLabors.ImageSharp.PixelFormats;
+
+namespace SixLabors.ImageSharp.Processing.Processors.Quantization;
+
+/// <summary>
+/// Defines a delegate for processing a row of pixels in an image for quantization.
+/// </summary>
+/// <typeparam name="TPixel">Represents a pixel type that can be processed in a quantizing operation.</typeparam>
+internal interface IQuantizingPixelRowDelegate<TPixel>
+    where TPixel : unmanaged, IPixel<TPixel>
+{
+    /// <summary>
+    /// Gets the transparent color mode to use when adding colors to the palette.
+    /// </summary>
+    public TransparentColorMode TransparentColorMode { get; }
+
+    /// <summary>
+    /// Processes a row of pixels for quantization.
+    /// </summary>
+    /// <param name="row">The row of pixels to process.</param>
+    /// <param name="rowIndex">The index of the row being processed.</param>
+    public void Invoke(ReadOnlySpan<TPixel> row, int rowIndex);
+}
diff --git a/src/ImageSharp/Processing/Processors/Quantization/OctreeQuantizer{TPixel}.cs b/src/ImageSharp/Processing/Processors/Quantization/OctreeQuantizer{TPixel}.cs
index 65e814e620..e094b18964 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/OctreeQuantizer{TPixel}.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/OctreeQuantizer{TPixel}.cs
@@ -6,6 +6,7 @@
 using System.Numerics;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
+using SixLabors.ImageSharp.Formats;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;
 
@@ -16,11 +17,10 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization;
 /// <see href="http://msdn.microsoft.com/en-us/library/aa479306.aspx"/>
 /// </summary>
 /// <typeparam name="TPixel">The pixel format.</typeparam>
-[SuppressMessage(
-    "Design",
-    "CA1001:Types that own disposable fields should be disposable",
-    Justification = "https://github.com/dotnet/roslyn-analyzers/issues/6151")]
+#pragma warning disable CA1001 // Types that own disposable fields should be disposable
+// See https://github.com/dotnet/roslyn-analyzers/issues/6151
 public struct OctreeQuantizer<TPixel> : IQuantizer<TPixel>
+#pragma warning restore CA1001 // Types that own disposable fields should be disposable
     where TPixel : unmanaged, IPixel<TPixel>
 {
     private readonly int maxColors;
@@ -28,15 +28,14 @@ public struct OctreeQuantizer<TPixel> : IQuantizer<TPixel>
     private readonly Octree octree;
     private readonly IMemoryOwner<TPixel> paletteOwner;
     private ReadOnlyMemory<TPixel> palette;
-    private EuclideanPixelMap<TPixel>? pixelMap;
+    private PixelMap<TPixel>? pixelMap;
     private readonly bool isDithering;
-    private readonly short transparencyThreshold;
     private bool isDisposed;
 
     /// <summary>
     /// Initializes a new instance of the <see cref="OctreeQuantizer{TPixel}"/> struct.
     /// </summary>
-    /// <param name="configuration">The configuration which allows altering default behaviour or extending the library.</param>
+    /// <param name="configuration">The configuration which allows altering default behavior or extending the library.</param>
     /// <param name="options">The quantizer options defining quantization rules.</param>
     [MethodImpl(InliningOptions.ShortMethod)]
     public OctreeQuantizer(Configuration configuration, QuantizerOptions options)
@@ -45,9 +44,8 @@ public OctreeQuantizer(Configuration configuration, QuantizerOptions options)
         this.Options = options;
 
         this.maxColors = this.Options.MaxColors;
-        this.transparencyThreshold = (short)(this.Options.TransparencyThreshold * 255);
         this.bitDepth = Numerics.Clamp(ColorNumerics.GetBitsNeededForColorDepth(this.maxColors), 1, 8);
-        this.octree = new Octree(this.bitDepth, this.maxColors, this.transparencyThreshold, configuration.MemoryAllocator);
+        this.octree = new Octree(configuration, this.bitDepth, this.maxColors, this.Options.TransparencyThreshold, this.Options.ThresholdReplacementColor);
         this.paletteOwner = configuration.MemoryAllocator.Allocate<TPixel>(this.maxColors, AllocationOptions.Clean);
         this.pixelMap = default;
         this.palette = default;
@@ -77,25 +75,13 @@ public ReadOnlyMemory<TPixel> Palette
     }
 
     /// <inheritdoc/>
-    public readonly void AddPaletteColors(in Buffer2DRegion<TPixel> pixelRegion)
+    public readonly void AddPaletteColors(in Buffer2DRegion<TPixel> pixelRegion, TransparentColorMode mode)
     {
-        using IMemoryOwner<Rgba32> buffer = this.Configuration.MemoryAllocator.Allocate<Rgba32>(pixelRegion.Width);
-        Span<Rgba32> bufferSpan = buffer.GetSpan();
-
-        // Loop through each row
-        for (int y = 0; y < pixelRegion.Height; y++)
-        {
-            Span<TPixel> row = pixelRegion.DangerousGetRowSpan(y);
-            PixelOperations<TPixel>.Instance.ToRgba32(this.Configuration, row, bufferSpan);
-
-            Octree octree = this.octree;
-            int transparencyThreshold = this.transparencyThreshold;
-            for (int x = 0; x < bufferSpan.Length; x++)
-            {
-                // Add the color to the Octree
-                octree.AddColor(bufferSpan[x]);
-            }
-        }
+        PixelRowDelegate pixelRowDelegate = new(this.octree, mode);
+        QuantizerUtilities.AddPaletteColors<OctreeQuantizer<TPixel>, TPixel, Rgba32, PixelRowDelegate>(
+            ref Unsafe.AsRef(in this),
+            in pixelRegion,
+            in pixelRowDelegate);
     }
 
     private void ResolvePalette()
@@ -108,7 +94,7 @@ private void ResolvePalette()
 
         if (this.isDithering)
         {
-            this.pixelMap = new EuclideanPixelMap<TPixel>(this.Configuration, result);
+            this.pixelMap = PixelMapFactory.Create(this.Configuration, result, this.Options.ColorMatchingMode);
         }
 
         this.palette = result;
@@ -117,7 +103,12 @@ private void ResolvePalette()
     /// <inheritdoc/>
     [MethodImpl(InliningOptions.ShortMethod)]
     public readonly IndexedImageFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> source, Rectangle bounds)
-        => QuantizerUtilities.QuantizeFrame(ref Unsafe.AsRef(in this), source, bounds);
+        => this.QuantizeFrame(source, bounds, TransparentColorMode.Preserve);
+
+    /// <inheritdoc/>
+    [MethodImpl(InliningOptions.ShortMethod)]
+    public readonly IndexedImageFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> source, Rectangle bounds, TransparentColorMode mode)
+        => QuantizerUtilities.QuantizeFrame(ref Unsafe.AsRef(in this), source, bounds, mode);
 
     /// <inheritdoc/>
     [MethodImpl(InliningOptions.ShortMethod)]
@@ -128,7 +119,7 @@ public readonly byte GetQuantizedColor(TPixel color, out TPixel match)
         // In this case, we must use the pixel map to get the closest color.
         if (this.isDithering)
         {
-            return (byte)this.pixelMap!.GetClosestColor(color, out match, this.transparencyThreshold);
+            return (byte)this.pixelMap!.GetClosestColor(color, out match);
         }
 
         ref TPixel paletteRef = ref MemoryMarshal.GetReference(this.palette.Span);
@@ -151,6 +142,21 @@ public void Dispose()
         }
     }
 
+    private readonly struct PixelRowDelegate : IQuantizingPixelRowDelegate<Rgba32>
+    {
+        private readonly Octree octree;
+
+        public PixelRowDelegate(Octree octree, TransparentColorMode mode)
+        {
+            this.octree = octree;
+            this.TransparentColorMode = mode;
+        }
+
+        public TransparentColorMode TransparentColorMode { get; }
+
+        public void Invoke(ReadOnlySpan<Rgba32> row, int rowIndex) => this.octree.AddColors(row);
+    }
+
     /// <summary>
     /// A hexadecatree-based color quantization structure used for fast color distance lookups and palette generation.
     /// This tree maintains a fixed pool of nodes (capacity 4096) where each node can have up to 16 children, stores
@@ -159,6 +165,9 @@ public void Dispose()
     /// </summary>
     internal sealed class Octree : IDisposable
     {
+        // The memory allocator.
+        private readonly MemoryAllocator allocator;
+
         // Pooled buffer for OctreeNodes.
         private readonly IMemoryOwner<OctreeNode> nodesOwner;
 
@@ -172,7 +181,7 @@ internal sealed class Octree : IDisposable
         private readonly int maxColorBits;
 
         // The threshold for transparent colors.
-        private readonly short transparencyThreshold;
+        private readonly int transparencyThreshold255;
 
         // Instead of a reference to the root, we store the index of the root node.
         // Index 0 is reserved for the root.
@@ -185,28 +194,43 @@ internal sealed class Octree : IDisposable
         private int previousNode;
         private Rgba32 previousColor;
 
+        // The color to use for pixels below the transparency threshold.
+        private Vector4 thresholdReplacementColor;
+        private Vector4 thresholdReplacementColorV4;
+        private readonly Rgba32 thresholdReplacementColorRgba;
+
         // Free list for reclaimed node indices.
         private readonly Stack<short> freeIndices = new();
 
         /// <summary>
         /// Initializes a new instance of the <see cref="Octree"/> class.
         /// </summary>
+        /// <param name="configuration">The configuration which allows altering default behavior or extending the library.</param>
         /// <param name="maxColorBits">The maximum number of significant bits in the image.</param>
         /// <param name="maxColors">The maximum number of colors to allow in the palette.</param>
         /// <param name="transparencyThreshold">The threshold for transparent colors.</param>
-        /// <param name="allocator">The memory allocator.</param>
-        public Octree(int maxColorBits, int maxColors, short transparencyThreshold, MemoryAllocator allocator)
+        /// <param name="thresholdReplacementColor">The color to use for pixels below the transparency threshold.</param>
+        public Octree(
+            Configuration configuration,
+            int maxColorBits,
+            int maxColors,
+            float transparencyThreshold,
+            Color thresholdReplacementColor)
         {
             this.maxColorBits = maxColorBits;
             this.maxColors = maxColors;
-            this.transparencyThreshold = transparencyThreshold;
+            this.transparencyThreshold255 = (int)(transparencyThreshold * 255F);
+            this.thresholdReplacementColor = thresholdReplacementColor.ToScaledVector4();
+            this.thresholdReplacementColorV4 = this.thresholdReplacementColor * 255F;
+            this.thresholdReplacementColorRgba = thresholdReplacementColor.ToPixel<Rgba32>();
             this.Leaves = 0;
             this.previousNode = -1;
             this.previousColor = default;
 
             // Allocate a conservative buffer for nodes.
             const int capacity = 4096;
-            this.nodesOwner = allocator.Allocate<OctreeNode>(capacity, AllocationOptions.Clean);
+            this.allocator = configuration.MemoryAllocator;
+            this.nodesOwner = this.allocator.Allocate<OctreeNode>(capacity, AllocationOptions.Clean);
 
             // Create the reducible nodes array (one per level 0 .. maxColorBits-1).
             this.reducibleNodes = new short[this.maxColorBits];
@@ -228,11 +252,23 @@ public Octree(int maxColorBits, int maxColors, short transparencyThreshold, Memo
         /// </summary>
         internal Span<OctreeNode> Nodes => this.nodesOwner.Memory.Span;
 
+        /// <summary>
+        /// Adds a span of colors to the octree.
+        /// </summary>
+        /// <param name="row">A span of color values to be added.</param>
+        public void AddColors(ReadOnlySpan<Rgba32> row)
+        {
+            for (int x = 0; x < row.Length; x++)
+            {
+                this.AddColor(row[x]);
+            }
+        }
+
         /// <summary>
         /// Add a color to the Octree.
         /// </summary>
         /// <param name="color">The color to add.</param>
-        public void AddColor(Rgba32 color)
+        private void AddColor(Rgba32 color)
         {
             // Ensure that the tree is not already full.
             if (this.nextNode >= this.Nodes.Length && this.freeIndices.Count == 0)
@@ -243,11 +279,6 @@ public void AddColor(Rgba32 color)
                 }
             }
 
-            if (color.A < this.transparencyThreshold)
-            {
-                color = default;
-            }
-
             // If the color is the same as the previous color, increment the node.
             // Otherwise, add a new node.
             if (this.previousColor.Equals(color))
@@ -540,9 +571,9 @@ public void ConstructPalette(Octree octree, Span<TPixel> palette, ref short pale
                         Vector4.Zero,
                         new Vector4(255));
 
-                    if (vector.W < octree.transparencyThreshold)
+                    if (vector.W < octree.transparencyThreshold255)
                     {
-                        vector = default;
+                        vector = octree.thresholdReplacementColorV4;
                     }
 
                     palette[paletteIndex] = TPixel.FromRgba32(new Rgba32((byte)vector.X, (byte)vector.Y, (byte)vector.Z, (byte)vector.W));
@@ -571,9 +602,9 @@ public void ConstructPalette(Octree octree, Span<TPixel> palette, ref short pale
             /// <param name="octree">The parent octree.</param>
             public int GetPaletteIndex(Rgba32 color, int level, Octree octree)
             {
-                if (color.A < octree.transparencyThreshold)
+                if (color.A < octree.transparencyThreshold255)
                 {
-                    color = default;
+                    color = octree.thresholdReplacementColorRgba;
                 }
 
                 if (this.Leaf)
diff --git a/src/ImageSharp/Processing/Processors/Quantization/PaletteQuantizer{TPixel}.cs b/src/ImageSharp/Processing/Processors/Quantization/PaletteQuantizer{TPixel}.cs
index d734b36c30..712204bbfe 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/PaletteQuantizer{TPixel}.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/PaletteQuantizer{TPixel}.cs
@@ -3,6 +3,7 @@
 
 using System.Diagnostics.CodeAnalysis;
 using System.Runtime.CompilerServices;
+using SixLabors.ImageSharp.Formats;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;
 
@@ -20,7 +21,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization;
 internal struct PaletteQuantizer<TPixel> : IQuantizer<TPixel>
     where TPixel : unmanaged, IPixel<TPixel>
 {
-    private readonly EuclideanPixelMap<TPixel> pixelMap;
+    private readonly PixelMap<TPixel> pixelMap;
     private int transparencyIndex;
     private TPixel transparentColor;
 
@@ -58,7 +59,7 @@ public PaletteQuantizer(
 
         this.Configuration = configuration;
         this.Options = options;
-        this.pixelMap = new EuclideanPixelMap<TPixel>(configuration, palette);
+        this.pixelMap = PixelMapFactory.Create(this.Configuration, palette, options.ColorMatchingMode);
         this.transparencyIndex = transparencyIndex;
         this.transparentColor = transparentColor;
     }
@@ -74,15 +75,25 @@ public PaletteQuantizer(
 
     /// <inheritdoc/>
     [MethodImpl(InliningOptions.ShortMethod)]
-    public readonly IndexedImageFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> source, Rectangle bounds)
-        => QuantizerUtilities.QuantizeFrame(ref Unsafe.AsRef(in this), source, bounds);
+    public readonly void AddPaletteColors(in Buffer2DRegion<TPixel> pixelRegion)
+        => this.AddPaletteColors(in pixelRegion, TransparentColorMode.Preserve);
 
     /// <inheritdoc/>
     [MethodImpl(InliningOptions.ShortMethod)]
-    public readonly void AddPaletteColors(in Buffer2DRegion<TPixel> pixelRegion)
+    public readonly void AddPaletteColors(in Buffer2DRegion<TPixel> pixelRegion, TransparentColorMode mode)
     {
     }
 
+    /// <inheritdoc/>
+    [MethodImpl(InliningOptions.ShortMethod)]
+    public readonly IndexedImageFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> source, Rectangle bounds)
+        => this.QuantizeFrame(source, bounds, TransparentColorMode.Preserve);
+
+    /// <inheritdoc/>
+    [MethodImpl(InliningOptions.ShortMethod)]
+    public readonly IndexedImageFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> source, Rectangle bounds, TransparentColorMode mode)
+        => QuantizerUtilities.QuantizeFrame(ref Unsafe.AsRef(in this), source, bounds, mode);
+
     /// <inheritdoc/>
     [MethodImpl(InliningOptions.ShortMethod)]
     public readonly byte GetQuantizedColor(TPixel color, out TPixel match)
diff --git a/src/ImageSharp/Processing/Processors/Quantization/QuantizerOptions.cs b/src/ImageSharp/Processing/Processors/Quantization/QuantizerOptions.cs
index 4f4104a8a3..7a66204c64 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/QuantizerOptions.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/QuantizerOptions.cs
@@ -49,4 +49,15 @@ public float TransparencyThreshold
         get => this.threshold;
         set => this.threshold = Numerics.Clamp(value, QuantizerConstants.MinTransparencyThreshold, QuantizerConstants.MaxTransparencyThreshold);
     }
+
+    /// <summary>
+    /// Gets or sets the color used for replacing colors with an alpha component below the threshold.
+    /// Defaults to <see cref="Color.Transparent"/>.
+    /// </summary>
+    public Color ThresholdReplacementColor { get; set; } = Color.Transparent;
+
+    /// <summary>
+    /// Gets or sets the color matching mode used for matching pixel values to palette colors.
+    /// </summary>
+    public ColorMatchingMode ColorMatchingMode { get; set; } = ColorMatchingMode.Hybrid;
 }
diff --git a/src/ImageSharp/Processing/Processors/Quantization/QuantizerUtilities.cs b/src/ImageSharp/Processing/Processors/Quantization/QuantizerUtilities.cs
index 49eaa79abb..d2d9d68b4f 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/QuantizerUtilities.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/QuantizerUtilities.cs
@@ -1,7 +1,11 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
+using System.Buffers;
+using System.Numerics;
 using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+using System.Runtime.Intrinsics;
 using SixLabors.ImageSharp.Formats;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;
@@ -14,6 +18,126 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization;
 /// </summary>
 public static class QuantizerUtilities
 {
+    /// <summary>
+    /// Determines if transparent pixels can be replaced based on the specified color mode and pixel type.
+    /// </summary>
+    /// <typeparam name="TPixel">The type of the pixel.</typeparam>
+    /// <param name="threshold">The alpha threshold used to determine if a pixel is transparent.</param>
+    /// <returns>Returns true if transparent pixels can be replaced; otherwise, false.</returns>
+    public static bool ShouldReplacePixelsByAlphaThreshold<TPixel>(float threshold)
+        where TPixel : unmanaged, IPixel<TPixel>
+        => threshold > 0 && TPixel.GetPixelTypeInfo().AlphaRepresentation == PixelAlphaRepresentation.Unassociated;
+
+    /// <summary>
+    /// Replaces transparent pixels in a span with a specified color based on an alpha threshold.
+    /// </summary>
+    /// <param name="source">A span of color vectors that will be checked for transparency and potentially modified.</param>
+    /// <param name="replacement">A color vector that will replace transparent pixels when the alpha value is below the specified threshold.</param>
+    /// <param name="threshold">The alpha threshold used to determine if a pixel is transparent.</param>
+    public static void ReplacePixelsByAlphaThreshold(Span<Vector4> source, Vector4 replacement, float threshold)
+    {
+        if (Vector512.IsHardwareAccelerated && source.Length >= 4)
+        {
+            Vector128<float> replacement128 = replacement.AsVector128();
+            Vector256<float> replacement256 = Vector256.Create(replacement128, replacement128);
+            Vector512<float> replacement512 = Vector512.Create(replacement256, replacement256);
+            Vector512<float> threshold512 = Vector512.Create(threshold);
+
+            Span<Vector512<float>> source512 = MemoryMarshal.Cast<Vector4, Vector512<float>>(source);
+            for (int i = 0; i < source512.Length; i++)
+            {
+                ref Vector512<float> v = ref source512[i];
+
+                // Do `vector < threshold`
+                Vector512<float> mask = Vector512.LessThan(v, threshold512);
+
+                // Replicate the result for W to all elements (is AllBitsSet if the W was less than threshold and Zero otherwise)
+                mask = Vector512.Shuffle(mask, Vector512.Create(3, 3, 3, 3, 7, 7, 7, 7, 11, 11, 11, 11, 15, 15, 15, 15));
+
+                // Use the mask to select the replacement vector
+                // (replacement & mask) | (v512 & ~mask)
+                v = Vector512.ConditionalSelect(mask, replacement512, v);
+            }
+
+            int m = Numerics.Modulo4(source.Length);
+            if (m != 0)
+            {
+                for (int i = source.Length - m; i < source.Length; i++)
+                {
+                    if (source[i].W < threshold)
+                    {
+                        source[i] = replacement;
+                    }
+                }
+            }
+        }
+        else if (Vector256.IsHardwareAccelerated && source.Length >= 2)
+        {
+            Vector128<float> replacement128 = replacement.AsVector128();
+            Vector256<float> replacement256 = Vector256.Create(replacement128, replacement128);
+            Vector256<float> threshold256 = Vector256.Create(threshold);
+
+            Span<Vector256<float>> source256 = MemoryMarshal.Cast<Vector4, Vector256<float>>(source);
+            for (int i = 0; i < source256.Length; i++)
+            {
+                ref Vector256<float> v = ref source256[i];
+
+                // Do `vector < threshold`
+                Vector256<float> mask = Vector256.LessThan(v, threshold256);
+
+                // Replicate the result for W to all elements (is AllBitsSet if the W was less than threshold and Zero otherwise)
+                mask = Vector256.Shuffle(mask, Vector256.Create(3, 3, 3, 3, 7, 7, 7, 7));
+
+                // Use the mask to select the replacement vector
+                // (replacement & mask) | (v256 & ~mask)
+                v = Vector256.ConditionalSelect(mask, replacement256, v);
+            }
+
+            int m = Numerics.Modulo2(source.Length);
+            if (m != 0)
+            {
+                for (int i = source.Length - m; i < source.Length; i++)
+                {
+                    if (source[i].W < threshold)
+                    {
+                        source[i] = replacement;
+                    }
+                }
+            }
+        }
+        else if (Vector128.IsHardwareAccelerated)
+        {
+            Vector128<float> replacement128 = replacement.AsVector128();
+            Vector128<float> threshold128 = Vector128.Create(threshold);
+
+            for (int i = 0; i < source.Length; i++)
+            {
+                ref Vector4 v = ref source[i];
+                Vector128<float> v128 = v.AsVector128();
+
+                // Do `vector < threshold`
+                Vector128<float> mask = Vector128.LessThan(v128, threshold128);
+
+                // Replicate the result for W to all elements (is AllBitsSet if the W was less than threshold and Zero otherwise)
+                mask = Vector128.Shuffle(mask, Vector128.Create(3, 3, 3, 3));
+
+                // Use the mask to select the replacement vector
+                // (replacement & mask) | (v128 & ~mask)
+                v = Vector128.ConditionalSelect(mask, replacement128, v128).AsVector4();
+            }
+        }
+        else
+        {
+            for (int i = 0; i < source.Length; i++)
+            {
+                if (source[i].W < threshold)
+                {
+                    source[i] = replacement;
+                }
+            }
+        }
+    }
+
     /// <summary>
     /// Helper method for throwing an exception when a frame quantizer palette has
     /// been requested but not built yet.
@@ -21,12 +145,13 @@ public static class QuantizerUtilities
     /// <typeparam name="TPixel">The pixel format.</typeparam>
     /// <param name="palette">The frame quantizer palette.</param>
     /// <exception cref="InvalidOperationException">
-    /// The palette has not been built via <see cref="IQuantizer{TPixel}.AddPaletteColors"/>
+    /// The palette has not been built via <see cref="IQuantizer{TPixel}.AddPaletteColors(in Buffer2DRegion{TPixel})"/>
     /// </exception>
+    [MethodImpl(InliningOptions.ColdPath)]
     public static void CheckPaletteState<TPixel>(in ReadOnlyMemory<TPixel> palette)
         where TPixel : unmanaged, IPixel<TPixel>
     {
-        if (palette.Equals(default))
+        if (palette.IsEmpty)
         {
             throw new InvalidOperationException("Frame Quantizer palette has not been built.");
         }
@@ -47,6 +172,29 @@ public static IndexedImageFrame<TPixel> BuildPaletteAndQuantizeFrame<TPixel>(
         ImageFrame<TPixel> source,
         Rectangle bounds)
         where TPixel : unmanaged, IPixel<TPixel>
+        => BuildPaletteAndQuantizeFrame(
+            quantizer,
+            source,
+            bounds,
+            TransparentColorMode.Preserve);
+
+    /// <summary>
+    /// Execute both steps of the quantization.
+    /// </summary>
+    /// <param name="quantizer">The pixel specific quantizer.</param>
+    /// <param name="source">The source image frame to quantize.</param>
+    /// <param name="bounds">The bounds within the frame to quantize.</param>
+    /// <param name="mode">The transparent color mode.</param>
+    /// <typeparam name="TPixel">The pixel type.</typeparam>
+    /// <returns>
+    /// A <see cref="IndexedImageFrame{TPixel}"/> representing a quantized version of the source frame pixels.
+    /// </returns>
+    public static IndexedImageFrame<TPixel> BuildPaletteAndQuantizeFrame<TPixel>(
+        this IQuantizer<TPixel> quantizer,
+        ImageFrame<TPixel> source,
+        Rectangle bounds,
+        TransparentColorMode mode)
+        where TPixel : unmanaged, IPixel<TPixel>
     {
         Guard.NotNull(quantizer, nameof(quantizer));
         Guard.NotNull(source, nameof(source));
@@ -54,8 +202,7 @@ public static IndexedImageFrame<TPixel> BuildPaletteAndQuantizeFrame<TPixel>(
         Rectangle interest = Rectangle.Intersect(source.Bounds, bounds);
         Buffer2DRegion<TPixel> region = source.PixelBuffer.GetRegion(interest);
 
-        // Collect the palette. Required before the second pass runs.
-        quantizer.AddPaletteColors(in region);
+        quantizer.AddPaletteColors(in region, mode);
         return quantizer.QuantizeFrame(source, bounds);
     }
 
@@ -67,13 +214,15 @@ public static IndexedImageFrame<TPixel> BuildPaletteAndQuantizeFrame<TPixel>(
     /// <param name="quantizer">The pixel specific quantizer.</param>
     /// <param name="source">The source image frame to quantize.</param>
     /// <param name="bounds">The bounds within the frame to quantize.</param>
+    /// <param name="mode">The transparent color mode.</param>
     /// <returns>
     /// A <see cref="IndexedImageFrame{TPixel}"/> representing a quantized version of the source frame pixels.
     /// </returns>
     public static IndexedImageFrame<TPixel> QuantizeFrame<TFrameQuantizer, TPixel>(
         ref TFrameQuantizer quantizer,
         ImageFrame<TPixel> source,
-        Rectangle bounds)
+        Rectangle bounds,
+        TransparentColorMode mode)
         where TFrameQuantizer : struct, IQuantizer<TPixel>
         where TPixel : unmanaged, IPixel<TPixel>
     {
@@ -88,13 +237,13 @@ public static IndexedImageFrame<TPixel> QuantizeFrame<TFrameQuantizer, TPixel>(
 
         if (quantizer.Options.Dither is null)
         {
-            SecondPass(ref quantizer, source, destination, interest);
+            SecondPass(ref quantizer, source, destination, interest, mode);
         }
         else
         {
             // We clone the image as we don't want to alter the original via error diffusion based dithering.
             using ImageFrame<TPixel> clone = source.Clone();
-            SecondPass(ref quantizer, clone, destination, interest);
+            SecondPass(ref quantizer, clone, destination, interest, mode);
         }
 
         return destination;
@@ -113,49 +262,28 @@ public static void BuildPalette<TPixel>(
         Image<TPixel> source)
         where TPixel : unmanaged, IPixel<TPixel>
         => quantizer.BuildPalette(
-            source.Configuration,
             TransparentColorMode.Preserve,
             pixelSamplingStrategy,
-            source,
-            Color.Transparent);
+            source);
 
     /// <summary>
     /// Adds colors to the quantized palette from the given pixel regions.
     /// </summary>
     /// <typeparam name="TPixel">The pixel format.</typeparam>
     /// <param name="quantizer">The pixel specific quantizer.</param>
-    /// <param name="configuration">The configuration.</param>
     /// <param name="mode">The transparent color mode.</param>
     /// <param name="pixelSamplingStrategy">The pixel sampling strategy.</param>
     /// <param name="source">The source image to sample from.</param>
-    /// <param name="backgroundColor">The background color to use when clearing transparent pixels.</param>
     public static void BuildPalette<TPixel>(
         this IQuantizer<TPixel> quantizer,
-        Configuration configuration,
         TransparentColorMode mode,
         IPixelSamplingStrategy pixelSamplingStrategy,
-        Image<TPixel> source,
-        Color backgroundColor)
+        Image<TPixel> source)
         where TPixel : unmanaged, IPixel<TPixel>
     {
-        if (EncodingUtilities.ShouldClearTransparentPixels<TPixel>(mode))
+        foreach (Buffer2DRegion<TPixel> region in pixelSamplingStrategy.EnumeratePixelRegions(source))
         {
-            foreach (Buffer2DRegion<TPixel> region in pixelSamplingStrategy.EnumeratePixelRegions(source))
-            {
-                // We need to clone the region to ensure we don't alter the original image.
-                using Buffer2D<TPixel> clone = region.Buffer.CloneRegion(configuration, region.Rectangle);
-                Buffer2DRegion<TPixel> clonedRegion = clone.GetRegion();
-
-                EncodingUtilities.ClearTransparentPixels(configuration, in clonedRegion, backgroundColor);
-                quantizer.AddPaletteColors(in clonedRegion);
-            }
-        }
-        else
-        {
-            foreach (Buffer2DRegion<TPixel> region in pixelSamplingStrategy.EnumeratePixelRegions(source))
-            {
-                quantizer.AddPaletteColors(in region);
-            }
+            quantizer.AddPaletteColors(in region, mode);
         }
     }
 
@@ -172,83 +300,208 @@ public static void BuildPalette<TPixel>(
         ImageFrame<TPixel> source)
         where TPixel : unmanaged, IPixel<TPixel>
         => quantizer.BuildPalette(
-            source.Configuration,
             TransparentColorMode.Preserve,
             pixelSamplingStrategy,
-            source,
-            Color.Transparent);
+            source);
 
     /// <summary>
     /// Adds colors to the quantized palette from the given pixel regions.
     /// </summary>
     /// <typeparam name="TPixel">The pixel format.</typeparam>
     /// <param name="quantizer">The pixel specific quantizer.</param>
-    /// <param name="configuration">The configuration.</param>
     /// <param name="mode">The transparent color mode.</param>
     /// <param name="pixelSamplingStrategy">The pixel sampling strategy.</param>
     /// <param name="source">The source image frame to sample from.</param>
-    /// <param name="backgroundColor">The background color to use when clearing transparent pixels.</param>
     public static void BuildPalette<TPixel>(
         this IQuantizer<TPixel> quantizer,
-        Configuration configuration,
         TransparentColorMode mode,
         IPixelSamplingStrategy pixelSamplingStrategy,
-        ImageFrame<TPixel> source,
-        Color backgroundColor)
+        ImageFrame<TPixel> source)
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        foreach (Buffer2DRegion<TPixel> region in pixelSamplingStrategy.EnumeratePixelRegions(source))
+        {
+            quantizer.AddPaletteColors(in region, mode);
+        }
+    }
+
+    internal static void AddPaletteColors<TFrameQuantizer, TPixel, TPixel2, TDelegate>(
+        ref TFrameQuantizer quantizer,
+        in Buffer2DRegion<TPixel> source,
+        in TDelegate rowDelegate)
+        where TFrameQuantizer : struct, IQuantizer<TPixel>
         where TPixel : unmanaged, IPixel<TPixel>
+        where TPixel2 : unmanaged, IPixel<TPixel2>
+        where TDelegate : struct, IQuantizingPixelRowDelegate<TPixel2>
     {
-        if (EncodingUtilities.ShouldClearTransparentPixels<TPixel>(mode))
+        Configuration configuration = quantizer.Configuration;
+        float threshold = quantizer.Options.TransparencyThreshold;
+        Color replacement = quantizer.Options.ThresholdReplacementColor;
+
+        using IMemoryOwner<TPixel2> delegateRowOwner = configuration.MemoryAllocator.Allocate<TPixel2>(source.Width);
+        Span<TPixel2> delegateRow = delegateRowOwner.Memory.Span;
+
+        bool replaceByThreshold = ShouldReplacePixelsByAlphaThreshold<TPixel>(threshold);
+        bool replaceTransparent = EncodingUtilities.ShouldReplaceTransparentPixels<TPixel>(rowDelegate.TransparentColorMode);
+
+        if (replaceByThreshold || replaceTransparent)
         {
-            // We need to clone the region to ensure we don't alter the original image.
-            foreach (Buffer2DRegion<TPixel> region in pixelSamplingStrategy.EnumeratePixelRegions(source))
+            using IMemoryOwner<Vector4> vectorRowOwner = configuration.MemoryAllocator.Allocate<Vector4>(source.Width);
+            Span<Vector4> vectorRow = vectorRowOwner.Memory.Span;
+            Vector4 replacementV4 = replacement.ToScaledVector4();
+
+            if (replaceByThreshold)
             {
-                using Buffer2D<TPixel> clone = region.Buffer.CloneRegion(configuration, region.Rectangle);
-                Buffer2DRegion<TPixel> clonedRegion = clone.GetRegion();
+                for (int y = 0; y < source.Height; y++)
+                {
+                    Span<TPixel> sourceRow = source.DangerousGetRowSpan(y);
+                    PixelOperations<TPixel>.Instance.ToVector4(configuration, sourceRow, vectorRow, PixelConversionModifiers.Scale);
+
+                    ReplacePixelsByAlphaThreshold(vectorRow, replacementV4, threshold);
 
-                EncodingUtilities.ClearTransparentPixels(configuration, in clonedRegion, backgroundColor);
-                quantizer.AddPaletteColors(in clonedRegion);
+                    PixelOperations<TPixel2>.Instance.FromVector4Destructive(configuration, vectorRow, delegateRow, PixelConversionModifiers.Scale);
+                    rowDelegate.Invoke(delegateRow, y);
+                }
+            }
+            else
+            {
+                for (int y = 0; y < source.Height; y++)
+                {
+                    Span<TPixel> sourceRow = source.DangerousGetRowSpan(y);
+                    PixelOperations<TPixel>.Instance.ToVector4(configuration, sourceRow, vectorRow, PixelConversionModifiers.Scale);
+
+                    EncodingUtilities.ReplaceTransparentPixels(vectorRow, replacementV4);
+
+                    PixelOperations<TPixel2>.Instance.FromVector4Destructive(configuration, vectorRow, delegateRow, PixelConversionModifiers.Scale);
+                    rowDelegate.Invoke(delegateRow, y);
+                }
             }
         }
         else
         {
-            foreach (Buffer2DRegion<TPixel> region in pixelSamplingStrategy.EnumeratePixelRegions(source))
+            for (int y = 0; y < source.Height; y++)
             {
-                quantizer.AddPaletteColors(in region);
+                Span<TPixel> sourceRow = source.DangerousGetRowSpan(y);
+                PixelOperations<TPixel>.Instance.To(configuration, sourceRow, delegateRow);
+                rowDelegate.Invoke(delegateRow, y);
             }
         }
     }
 
-    [MethodImpl(InliningOptions.ShortMethod)]
     private static void SecondPass<TFrameQuantizer, TPixel>(
         ref TFrameQuantizer quantizer,
         ImageFrame<TPixel> source,
         IndexedImageFrame<TPixel> destination,
-        Rectangle bounds)
+        Rectangle bounds,
+        TransparentColorMode mode)
         where TFrameQuantizer : struct, IQuantizer<TPixel>
         where TPixel : unmanaged, IPixel<TPixel>
     {
+        float threshold = quantizer.Options.TransparencyThreshold;
+        Color replacement = quantizer.Options.ThresholdReplacementColor;
+        bool replaceByThreshold = ShouldReplacePixelsByAlphaThreshold<TPixel>(threshold);
+        bool replaceTransparent = EncodingUtilities.ShouldReplaceTransparentPixels<TPixel>(mode);
+        Vector4 replacementV4 = replacement.ToScaledVector4();
+
         IDither? dither = quantizer.Options.Dither;
         Buffer2D<TPixel> sourceBuffer = source.PixelBuffer;
+        Buffer2DRegion<TPixel> region = sourceBuffer.GetRegion(bounds);
+
+        Configuration configuration = quantizer.Configuration;
+        using IMemoryOwner<Vector4> vectorOwner = configuration.MemoryAllocator.Allocate<Vector4>(region.Width);
+        Span<Vector4> vectorRow = vectorOwner.Memory.Span;
 
         if (dither is null)
         {
-            int offsetY = bounds.Top;
-            int offsetX = bounds.Left;
+            using IMemoryOwner<TPixel> quantizingRowOwner = configuration.MemoryAllocator.Allocate<TPixel>(region.Width);
+            Span<TPixel> quantizingRow = quantizingRowOwner.Memory.Span;
 
-            for (int y = 0; y < destination.Height; y++)
+            // This is NOT a clone so we DO NOT write back to the source.
+            if (replaceByThreshold || replaceTransparent)
             {
-                ReadOnlySpan<TPixel> sourceRow = sourceBuffer.DangerousGetRowSpan(y + offsetY);
+                if (replaceByThreshold)
+                {
+                    for (int y = 0; y < region.Height; y++)
+                    {
+                        Span<TPixel> sourceRow = region.DangerousGetRowSpan(y);
+                        PixelOperations<TPixel>.Instance.ToVector4(configuration, sourceRow, vectorRow, PixelConversionModifiers.Scale);
+
+                        ReplacePixelsByAlphaThreshold(vectorRow, replacementV4, threshold);
+
+                        PixelOperations<TPixel>.Instance.FromVector4Destructive(configuration, vectorRow, quantizingRow, PixelConversionModifiers.Scale);
+
+                        Span<byte> destinationRow = destination.GetWritablePixelRowSpanUnsafe(y);
+                        for (int x = 0; x < destinationRow.Length; x++)
+                        {
+                            destinationRow[x] = quantizer.GetQuantizedColor(quantizingRow[x], out TPixel _);
+                        }
+                    }
+                }
+                else
+                {
+                    for (int y = 0; y < region.Height; y++)
+                    {
+                        Span<TPixel> sourceRow = region.DangerousGetRowSpan(y);
+                        PixelOperations<TPixel>.Instance.ToVector4(configuration, sourceRow, vectorRow, PixelConversionModifiers.Scale);
+
+                        EncodingUtilities.ReplaceTransparentPixels(vectorRow, replacementV4);
+
+                        PixelOperations<TPixel>.Instance.FromVector4Destructive(configuration, vectorRow, quantizingRow, PixelConversionModifiers.Scale);
+
+                        Span<byte> destinationRow = destination.GetWritablePixelRowSpanUnsafe(y);
+                        for (int x = 0; x < destinationRow.Length; x++)
+                        {
+                            destinationRow[x] = quantizer.GetQuantizedColor(quantizingRow[x], out TPixel _);
+                        }
+                    }
+                }
+
+                return;
+            }
+
+            for (int y = 0; y < region.Height; y++)
+            {
+                ReadOnlySpan<TPixel> sourceRow = region.DangerousGetRowSpan(y);
                 Span<byte> destinationRow = destination.GetWritablePixelRowSpanUnsafe(y);
 
                 for (int x = 0; x < destinationRow.Length; x++)
                 {
-                    destinationRow[x] = Unsafe.AsRef(in quantizer).GetQuantizedColor(sourceRow[x + offsetX], out TPixel _);
+                    destinationRow[x] = quantizer.GetQuantizedColor(sourceRow[x], out TPixel _);
                 }
             }
 
             return;
         }
 
+        // This is a clone so we write back to the source.
+        if (replaceByThreshold || replaceTransparent)
+        {
+            if (replaceByThreshold)
+            {
+                for (int y = 0; y < region.Height; y++)
+                {
+                    Span<TPixel> sourceRow = region.DangerousGetRowSpan(y);
+                    PixelOperations<TPixel>.Instance.ToVector4(configuration, sourceRow, vectorRow, PixelConversionModifiers.Scale);
+
+                    ReplacePixelsByAlphaThreshold(vectorRow, replacementV4, threshold);
+
+                    PixelOperations<TPixel>.Instance.FromVector4Destructive(configuration, vectorRow, sourceRow, PixelConversionModifiers.Scale);
+                }
+            }
+            else
+            {
+                for (int y = 0; y < region.Height; y++)
+                {
+                    Span<TPixel> sourceRow = region.DangerousGetRowSpan(y);
+                    PixelOperations<TPixel>.Instance.ToVector4(configuration, sourceRow, vectorRow, PixelConversionModifiers.Scale);
+
+                    EncodingUtilities.ReplaceTransparentPixels(vectorRow, replacementV4);
+
+                    PixelOperations<TPixel>.Instance.FromVector4Destructive(configuration, vectorRow, sourceRow, PixelConversionModifiers.Scale);
+                }
+            }
+        }
+
         dither.ApplyQuantizationDither(ref quantizer, source, destination, bounds);
     }
 }
diff --git a/src/ImageSharp/Processing/Processors/Quantization/WuQuantizer{TPixel}.cs b/src/ImageSharp/Processing/Processors/Quantization/WuQuantizer{TPixel}.cs
index db6490259f..a132aa2813 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/WuQuantizer{TPixel}.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/WuQuantizer{TPixel}.cs
@@ -6,6 +6,7 @@
 using System.Numerics;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
+using SixLabors.ImageSharp.Formats;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;
 
@@ -43,30 +44,10 @@ internal struct WuQuantizer<TPixel> : IQuantizer<TPixel>
     // The following two variables determine the amount of bits to preserve when calculating the histogram.
     // Reducing the value of these numbers the granularity of the color maps produced, making it much faster
     // and using much less memory but potentially less accurate. Current results are very good though!
-
-    /// <summary>
-    /// The index bits. 6 in original code.
-    /// </summary>
     private const int IndexBits = 5;
-
-    /// <summary>
-    /// The index alpha bits. 3 in original code.
-    /// </summary>
     private const int IndexAlphaBits = 5;
-
-    /// <summary>
-    /// The index count.
-    /// </summary>
     private const int IndexCount = (1 << IndexBits) + 1;
-
-    /// <summary>
-    /// The index alpha count.
-    /// </summary>
     private const int IndexAlphaCount = (1 << IndexAlphaBits) + 1;
-
-    /// <summary>
-    /// The table length. Now 1185921. originally 2471625.
-    /// </summary>
     private const int TableLength = IndexCount * IndexCount * IndexCount * IndexAlphaCount;
 
     private readonly IMemoryOwner<Moment> momentsOwner;
@@ -74,17 +55,18 @@ internal struct WuQuantizer<TPixel> : IQuantizer<TPixel>
     private readonly IMemoryOwner<TPixel> paletteOwner;
     private ReadOnlyMemory<TPixel> palette;
     private int maxColors;
-    private readonly float transparencyThreshold;
-    private readonly short transparencyThreshold255;
     private readonly Box[] colorCube;
-    private EuclideanPixelMap<TPixel>? pixelMap;
+    private PixelMap<TPixel>? pixelMap;
     private readonly bool isDithering;
+    private readonly int transparencyThreshold255;
+    private Vector4 thresholdReplacementColorV4;
+    private readonly Rgba32 thresholdReplacementColorRgba;
     private bool isDisposed;
 
     /// <summary>
     /// Initializes a new instance of the <see cref="WuQuantizer{TPixel}"/> struct.
     /// </summary>
-    /// <param name="configuration">The configuration which allows altering default behaviour or extending the library.</param>
+    /// <param name="configuration">The configuration which allows altering default behavior or extending the library.</param>
     /// <param name="options">The quantizer options defining quantization rules.</param>
     [MethodImpl(InliningOptions.ShortMethod)]
     public WuQuantizer(Configuration configuration, QuantizerOptions options)
@@ -104,8 +86,9 @@ public WuQuantizer(Configuration configuration, QuantizerOptions options)
         this.pixelMap = default;
         this.palette = default;
         this.isDithering = this.Options.Dither is not null;
-        this.transparencyThreshold = this.Options.TransparencyThreshold;
-        this.transparencyThreshold255 = (short)(this.Options.TransparencyThreshold * 255);
+        this.transparencyThreshold255 = (int)(this.Options.TransparencyThreshold * 255F);
+        this.thresholdReplacementColorV4 = this.Options.ThresholdReplacementColor.ToScaledVector4();
+        this.thresholdReplacementColorRgba = this.Options.ThresholdReplacementColor.ToPixel<Rgba32>();
     }
 
     /// <inheritdoc/>
@@ -130,8 +113,14 @@ public ReadOnlyMemory<TPixel> Palette
     }
 
     /// <inheritdoc/>
-    public readonly void AddPaletteColors(in Buffer2DRegion<TPixel> pixelRegion)
-        => this.Build3DHistogram(pixelRegion);
+    public readonly void AddPaletteColors(in Buffer2DRegion<TPixel> pixelRegion, TransparentColorMode mode)
+    {
+        PixelRowDelegate pixelRowDelegate = new(ref Unsafe.AsRef(in this), mode);
+        QuantizerUtilities.AddPaletteColors<WuQuantizer<TPixel>, TPixel, Rgba32, PixelRowDelegate>(
+            ref Unsafe.AsRef(in this),
+            in pixelRegion,
+            in pixelRowDelegate);
+    }
 
     /// <summary>
     /// Once all histogram data has been accumulated, this method computes the moments,
@@ -148,6 +137,9 @@ private void ResolvePalette()
         // Compute the palette colors from the resolved cubes.
         Span<TPixel> paletteSpan = this.paletteOwner.GetSpan()[..this.maxColors];
         ReadOnlySpan<Moment> momentsSpan = this.momentsOwner.GetSpan();
+
+        float transparencyThreshold = this.Options.TransparencyThreshold;
+        Vector4 thresholdReplacementColor = this.thresholdReplacementColorV4;
         for (int k = 0; k < paletteSpan.Length; k++)
         {
             this.Mark(ref this.colorCube[k], (byte)k);
@@ -155,9 +147,9 @@ private void ResolvePalette()
             if (moment.Weight > 0)
             {
                 Vector4 normalized = moment.Normalize();
-                if (normalized.W < this.transparencyThreshold)
+                if (normalized.W < transparencyThreshold)
                 {
-                    normalized = Vector4.Zero;
+                    normalized = thresholdReplacementColor;
                 }
 
                 paletteSpan[k] = TPixel.FromScaledVector4(normalized);
@@ -170,14 +162,19 @@ private void ResolvePalette()
         // Create the pixel map if dithering is enabled.
         if (this.isDithering && this.pixelMap is null)
         {
-            this.pixelMap = new EuclideanPixelMap<TPixel>(this.Configuration, this.palette);
+            this.pixelMap = PixelMapFactory.Create(this.Configuration, this.palette, this.Options.ColorMatchingMode);
         }
     }
 
     /// <inheritdoc/>
     [MethodImpl(InliningOptions.ShortMethod)]
     public readonly IndexedImageFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> source, Rectangle bounds)
-        => QuantizerUtilities.QuantizeFrame(ref Unsafe.AsRef(in this), source, bounds);
+        => this.QuantizeFrame(source, bounds, TransparentColorMode.Preserve);
+
+    /// <inheritdoc/>
+    [MethodImpl(InliningOptions.ShortMethod)]
+    public readonly IndexedImageFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> source, Rectangle bounds, TransparentColorMode mode)
+        => QuantizerUtilities.QuantizeFrame(ref Unsafe.AsRef(in this), source, bounds, mode);
 
     /// <inheritdoc/>
     public readonly byte GetQuantizedColor(TPixel color, out TPixel match)
@@ -187,13 +184,13 @@ public readonly byte GetQuantizedColor(TPixel color, out TPixel match)
         // In this case, we must use the pixel map to get the closest color.
         if (this.isDithering)
         {
-            return (byte)this.pixelMap!.GetClosestColor(color, out match, this.transparencyThreshold255);
+            return (byte)this.pixelMap!.GetClosestColor(color, out match);
         }
 
         Rgba32 rgba = color.ToRgba32();
         if (rgba.A < this.transparencyThreshold255)
         {
-            rgba = default;
+            rgba = this.thresholdReplacementColorRgba;
         }
 
         const int shift = 8 - IndexBits;
@@ -376,37 +373,19 @@ private static Moment Top(ref Box cube, int direction, int position, ReadOnlySpa
     /// <summary>
     /// Builds a 3-D color histogram of <c>counts, r/g/b, c^2</c>.
     /// </summary>
-    /// <param name="source">The source pixel data.</param>
-    private readonly void Build3DHistogram(in Buffer2DRegion<TPixel> source)
+    /// <param name="pixels">The source pixel data.</param>
+    private readonly void Build3DHistogram(ReadOnlySpan<Rgba32> pixels)
     {
-        Span<Moment> momentSpan = this.momentsOwner.GetSpan();
-
-        // Build up the 3-D color histogram
-        using IMemoryOwner<Rgba32> buffer = this.memoryAllocator.Allocate<Rgba32>(source.Width);
-        Span<Rgba32> bufferSpan = buffer.GetSpan();
-
-        float transparencyThreshold = this.Options.TransparencyThreshold * 255;
-
-        for (int y = 0; y < source.Height; y++)
+        Span<Moment> moments = this.momentsOwner.GetSpan();
+        for (int x = 0; x < pixels.Length; x++)
         {
-            Span<TPixel> row = source.DangerousGetRowSpan(y);
-            PixelOperations<TPixel>.Instance.ToRgba32(this.Configuration, row, bufferSpan);
-
-            for (int x = 0; x < bufferSpan.Length; x++)
-            {
-                Rgba32 rgba = bufferSpan[x];
-                if (rgba.A < transparencyThreshold)
-                {
-                    rgba = default;
-                }
-
-                int r = (rgba.R >> (8 - IndexBits)) + 1;
-                int g = (rgba.G >> (8 - IndexBits)) + 1;
-                int b = (rgba.B >> (8 - IndexBits)) + 1;
-                int a = (rgba.A >> (8 - IndexAlphaBits)) + 1;
+            Rgba32 rgba = pixels[x];
+            int r = (rgba.R >> (8 - IndexBits)) + 1;
+            int g = (rgba.G >> (8 - IndexBits)) + 1;
+            int b = (rgba.B >> (8 - IndexBits)) + 1;
+            int a = (rgba.A >> (8 - IndexAlphaBits)) + 1;
 
-                momentSpan[GetPaletteIndex(r, g, b, a)] += rgba;
-            }
+            moments[GetPaletteIndex(r, g, b, a)] += rgba;
         }
     }
 
@@ -918,4 +897,19 @@ public override readonly int GetHashCode()
             return hash.ToHashCode();
         }
     }
+
+    private readonly struct PixelRowDelegate : IQuantizingPixelRowDelegate<Rgba32>
+    {
+        private readonly WuQuantizer<TPixel> quantizer;
+
+        public PixelRowDelegate(ref WuQuantizer<TPixel> quantizer, TransparentColorMode mode)
+        {
+            this.quantizer = quantizer;
+            this.TransparentColorMode = mode;
+        }
+
+        public TransparentColorMode TransparentColorMode { get; }
+
+        public void Invoke(ReadOnlySpan<Rgba32> row, int rowIndex) => this.quantizer.Build3DHistogram(row);
+    }
 }
diff --git a/tests/ImageSharp.Tests/Formats/Gif/GifEncoderTests.cs b/tests/ImageSharp.Tests/Formats/Gif/GifEncoderTests.cs
index 748f505cce..44ed5e38dd 100644
--- a/tests/ImageSharp.Tests/Formats/Gif/GifEncoderTests.cs
+++ b/tests/ImageSharp.Tests/Formats/Gif/GifEncoderTests.cs
@@ -56,7 +56,7 @@ public void EncodeGeneratedPatterns<TPixel>(TestImageProvider<TPixel> provider,
             {
                 // Use the palette quantizer without dithering to ensure results
                 // are consistent
-                Quantizer = new WebSafePaletteQuantizer(new QuantizerOptions { Dither = null })
+                Quantizer = new WebSafePaletteQuantizer(new QuantizerOptions { Dither = null, TransparencyThreshold = 0 })
             };
 
             // Always save as we need to compare the encoded output.
diff --git a/tests/ImageSharp.Tests/Formats/Png/PngEncoderTests.cs b/tests/ImageSharp.Tests/Formats/Png/PngEncoderTests.cs
index 2a53e4de79..6836b98500 100644
--- a/tests/ImageSharp.Tests/Formats/Png/PngEncoderTests.cs
+++ b/tests/ImageSharp.Tests/Formats/Png/PngEncoderTests.cs
@@ -419,8 +419,8 @@ public void Encode_APng<TPixel>(TestImageProvider<TPixel> provider)
 
         using Image<Rgba32> output = Image.Load<Rgba32>(memStream);
 
-        // some loss from original, due to compositing
-        ImageComparer.TolerantPercentage(0.01f).VerifySimilarity(output, image);
+        // Some loss from original, due to palette matching accuracy.
+        ImageComparer.TolerantPercentage(0.172F).VerifySimilarity(output, image);
 
         Assert.Equal(image.Frames.Count, output.Frames.Count);
 

From 86b99170491f2fea53fdef65fb0046f0421d266e Mon Sep 17 00:00:00 2001
From: James Jackson-South <james_south@hotmail.com>
Date: Thu, 27 Mar 2025 10:00:36 +1000
Subject: [PATCH 08/18] Upstream V3 changes.

---
 src/ImageSharp/Advanced/AotCompilerTools.cs   | 17 +++-
 src/ImageSharp/Formats/Png/PngDecoderCore.cs  | 78 ++++++++++++++++++-
 src/ImageSharp/Formats/Png/PngEncoderCore.cs  | 11 ++-
 .../Quantization/IColorIndexCache.cs          | 18 ++---
 .../Formats/Png/PngEncoderTests.cs            |  1 +
 tests/ImageSharp.Tests/TestImages.cs          |  1 +
 tests/Images/Input/Png/issues/Issue_2882.png  |  3 +
 7 files changed, 114 insertions(+), 15 deletions(-)
 create mode 100644 tests/Images/Input/Png/issues/Issue_2882.png

diff --git a/src/ImageSharp/Advanced/AotCompilerTools.cs b/src/ImageSharp/Advanced/AotCompilerTools.cs
index 0d5faabe18..23bf85cf3d 100644
--- a/src/ImageSharp/Advanced/AotCompilerTools.cs
+++ b/src/ImageSharp/Advanced/AotCompilerTools.cs
@@ -138,10 +138,11 @@ private static void Seed<TPixel>()
         AotCompileResamplers<TPixel>();
         AotCompileQuantizers<TPixel>();
         AotCompilePixelSamplingStrategys<TPixel>();
+        AotCompilePixelMaps<TPixel>();
         AotCompileDithers<TPixel>();
         AotCompileMemoryManagers<TPixel>();
 
-        Unsafe.SizeOf<TPixel>();
+        _ = Unsafe.SizeOf<TPixel>();
 
         // TODO: Do the discovery work to figure out what works and what doesn't.
     }
@@ -514,6 +515,20 @@ private static void AotCompilePixelSamplingStrategys<TPixel>()
         default(ExtensivePixelSamplingStrategy).EnumeratePixelRegions(default(ImageFrame<TPixel>));
     }
 
+    /// <summary>
+    /// This method pre-seeds the all <see cref="IColorIndexCache{T}" /> in the AoT compiler.
+    /// </summary>
+    /// <typeparam name="TPixel">The pixel format.</typeparam>
+    [Preserve]
+    private static void AotCompilePixelMaps<TPixel>()
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        default(EuclideanPixelMap<TPixel, HybridCache>).GetClosestColor(default, out _);
+        default(EuclideanPixelMap<TPixel, AccurateCache>).GetClosestColor(default, out _);
+        default(EuclideanPixelMap<TPixel, CoarseCache>).GetClosestColor(default, out _);
+        default(EuclideanPixelMap<TPixel, NullCache>).GetClosestColor(default, out _);
+    }
+
     /// <summary>
     /// This method pre-seeds the all <see cref="IDither" /> in the AoT compiler.
     /// </summary>
diff --git a/src/ImageSharp/Formats/Png/PngDecoderCore.cs b/src/ImageSharp/Formats/Png/PngDecoderCore.cs
index 484241d52f..9df6f14bf7 100644
--- a/src/ImageSharp/Formats/Png/PngDecoderCore.cs
+++ b/src/ImageSharp/Formats/Png/PngDecoderCore.cs
@@ -1086,7 +1086,7 @@ private void ProcessDefilteredScanline<TPixel>(
             {
                 PixelBlender<TPixel> blender =
                     PixelOperations<TPixel>.Instance.GetPixelBlender(PixelColorBlendingMode.Normal, PixelAlphaCompositionMode.SrcOver);
-                blender.Blend<TPixel>(this.configuration, destination, destination, rowSpan, 1f);
+                blender.Blend(this.configuration, destination, destination, rowSpan, 1f);
             }
         }
         finally
@@ -1208,7 +1208,7 @@ private void ProcessInterlacedDefilteredScanline<TPixel>(
             {
                 PixelBlender<TPixel> blender =
                     PixelOperations<TPixel>.Instance.GetPixelBlender(PixelColorBlendingMode.Normal, PixelAlphaCompositionMode.SrcOver);
-                blender.Blend<TPixel>(this.configuration, destination, destination, rowSpan, 1f);
+                blender.Blend(this.configuration, destination, destination, rowSpan, 1F);
             }
         }
         finally
@@ -1866,6 +1866,9 @@ private bool TryReadChunk(Span<byte> buffer, out PngChunk chunk)
             return false;
         }
 
+        // Capture the current position so we can revert back to it if we fail to read a valid chunk.
+        long position = this.currentStream.Position;
+
         if (!this.TryReadChunkLength(buffer, out int length))
         {
             // IEND
@@ -1884,7 +1887,48 @@ private bool TryReadChunk(Span<byte> buffer, out PngChunk chunk)
             }
         }
 
-        PngChunkType type = this.ReadChunkType(buffer);
+        PngChunkType type;
+
+        // Loop until we get a chunk type that is valid.
+        while (true)
+        {
+            type = this.ReadChunkType(buffer);
+            if (!IsValidChunkType(type))
+            {
+                // The chunk type is invalid.
+                // Revert back to the next byte past the previous position and try again.
+                this.currentStream.Position = ++position;
+
+                // If we are now at the end of the stream, we're done.
+                if (this.currentStream.Position >= this.currentStream.Length)
+                {
+                    chunk = default;
+                    return false;
+                }
+
+                // Read the next chunk’s length.
+                if (!this.TryReadChunkLength(buffer, out length))
+                {
+                    chunk = default;
+                    return false;
+                }
+
+                while (length < 0)
+                {
+                    if (!this.TryReadChunkLength(buffer, out length))
+                    {
+                        chunk = default;
+                        return false;
+                    }
+                }
+
+                // Continue to try reading the next chunk.
+                continue;
+            }
+
+            // We have a valid chunk type.
+            break;
+        }
 
         // If we're reading color metadata only we're only interested in the IHDR and tRNS chunks.
         // We can skip most other chunk data in the stream for better performance.
@@ -1901,7 +1945,7 @@ private bool TryReadChunk(Span<byte> buffer, out PngChunk chunk)
 
         // A chunk might report a length that exceeds the length of the stream.
         // Take the minimum of the two values to ensure we don't read past the end of the stream.
-        long position = this.currentStream.Position;
+        position = this.currentStream.Position;
         chunk = new PngChunk(
             length: (int)Math.Min(length, this.currentStream.Length - position),
             type: type,
@@ -1919,6 +1963,32 @@ private bool TryReadChunk(Span<byte> buffer, out PngChunk chunk)
         return true;
     }
 
+    /// <summary>
+    /// Determines whether the 4-byte chunk type is valid (all ASCII letters).
+    /// </summary>
+    /// <param name="type">The chunk type.</param>
+    [MethodImpl(InliningOptions.ShortMethod)]
+    private static bool IsValidChunkType(PngChunkType type)
+    {
+        uint value = (uint)type;
+        byte b0 = (byte)(value >> 24);
+        byte b1 = (byte)(value >> 16);
+        byte b2 = (byte)(value >> 8);
+        byte b3 = (byte)value;
+        return IsAsciiLetter(b0) && IsAsciiLetter(b1) && IsAsciiLetter(b2) && IsAsciiLetter(b3);
+    }
+
+    /// <summary>
+    /// Returns a value indicating whether the given byte is an ASCII letter.
+    /// </summary>
+    /// <param name="b">The byte to check.</param>
+    /// <returns>
+    /// <see langword="true"/> if the byte is an ASCII letter; otherwise, <see langword="false"/>.
+    /// </returns>
+    [MethodImpl(InliningOptions.ShortMethod)]
+    private static bool IsAsciiLetter(byte b)
+        => (b >= (byte)'A' && b <= (byte)'Z') || (b >= (byte)'a' && b <= (byte)'z');
+
     /// <summary>
     /// Validates the png chunk.
     /// </summary>
diff --git a/src/ImageSharp/Formats/Png/PngEncoderCore.cs b/src/ImageSharp/Formats/Png/PngEncoderCore.cs
index c05c7e8289..6eecff8eda 100644
--- a/src/ImageSharp/Formats/Png/PngEncoderCore.cs
+++ b/src/ImageSharp/Formats/Png/PngEncoderCore.cs
@@ -290,7 +290,16 @@ public void Encode<TPixel>(Image<TPixel> image, Stream stream, CancellationToken
 
                     frameMetadata = currentFrame.Metadata.GetPngMetadata();
 
-                    bool blend = frameMetadata.BlendMode == FrameBlendMode.Over;
+                    // Determine whether to blend the current frame over the existing canvas.
+                    // Blending is applied only when the blend method is 'Over' (source-over blending)
+                    // and when the frame's disposal method is not 'RestoreToPrevious', which indicates that
+                    // the frame should not permanently alter the canvas.
+                    bool blend = frameMetadata.BlendMode == FrameBlendMode.Over
+                                 && frameMetadata.DisposalMode != FrameDisposalMode.RestoreToPrevious;
+
+                    // Establish the background color for the current frame.
+                    // If the disposal method is 'RestoreToBackground', use the predefined background color;
+                    // otherwise, use transparent, as no explicit background restoration is needed.
                     Color background = frameMetadata.DisposalMode == FrameDisposalMode.RestoreToBackground
                         ? this.backgroundColor.Value
                         : Color.Transparent;
diff --git a/src/ImageSharp/Processing/Processors/Quantization/IColorIndexCache.cs b/src/ImageSharp/Processing/Processors/Quantization/IColorIndexCache.cs
index 52efc62b7e..4e4fa5f0ac 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/IColorIndexCache.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/IColorIndexCache.cs
@@ -69,11 +69,11 @@ internal interface IColorIndexCache<T> : IColorIndexCache
 internal unsafe struct HybridCache : IColorIndexCache<HybridCache>
 {
     private CoarseCache coarseCache;
-    private ExactCache exactCache;
+    private AccurateCache accurateCache;
 
     public HybridCache(MemoryAllocator allocator)
     {
-        this.exactCache = ExactCache.Create(allocator);
+        this.accurateCache = AccurateCache.Create(allocator);
         this.coarseCache = CoarseCache.Create(allocator);
     }
 
@@ -84,7 +84,7 @@ public HybridCache(MemoryAllocator allocator)
     [MethodImpl(InliningOptions.ShortMethod)]
     public bool TryAdd(Rgba32 color, short index)
     {
-        if (this.exactCache.TryAdd(color, index))
+        if (this.accurateCache.TryAdd(color, index))
         {
             return true;
         }
@@ -96,7 +96,7 @@ public bool TryAdd(Rgba32 color, short index)
     [MethodImpl(InliningOptions.ShortMethod)]
     public readonly bool TryGetValue(Rgba32 color, out short value)
     {
-        if (this.exactCache.TryGetValue(color, out value))
+        if (this.accurateCache.TryGetValue(color, out value))
         {
             return true;
         }
@@ -107,14 +107,14 @@ public readonly bool TryGetValue(Rgba32 color, out short value)
     /// <inheritdoc/>
     public readonly void Clear()
     {
-        this.exactCache.Clear();
+        this.accurateCache.Clear();
         this.coarseCache.Clear();
     }
 
     /// <inheritdoc/>
     public void Dispose()
     {
-        this.exactCache.Dispose();
+        this.accurateCache.Dispose();
         this.coarseCache.Dispose();
     }
 }
@@ -311,7 +311,7 @@ public void Add(byte quantizedAlpha, short paletteIndex)
 /// typically very short; in the worst-case, the number of iterations is bounded by 256.
 /// This guarantees highly efficient and predictable performance for small, fixed-size color palettes.
 /// </remarks>
-internal unsafe struct ExactCache : IColorIndexCache<ExactCache>
+internal unsafe struct AccurateCache : IColorIndexCache<AccurateCache>
 {
     // Buckets array: each bucket holds the index (0-based) into the entries array
     // of the first entry in the chain, or -1 if empty.
@@ -326,7 +326,7 @@ internal unsafe struct ExactCache : IColorIndexCache<ExactCache>
 
     public const int Capacity = 512;
 
-    private ExactCache(MemoryAllocator allocator)
+    private AccurateCache(MemoryAllocator allocator)
     {
         this.Count = 0;
 
@@ -346,7 +346,7 @@ private ExactCache(MemoryAllocator allocator)
     public int Count { get; private set; }
 
     /// <inheritdoc/>
-    public static ExactCache Create(MemoryAllocator allocator) => new(allocator);
+    public static AccurateCache Create(MemoryAllocator allocator) => new(allocator);
 
     /// <inheritdoc/>
     [MethodImpl(InliningOptions.ShortMethod)]
diff --git a/tests/ImageSharp.Tests/Formats/Png/PngEncoderTests.cs b/tests/ImageSharp.Tests/Formats/Png/PngEncoderTests.cs
index 6836b98500..9d29b3bad5 100644
--- a/tests/ImageSharp.Tests/Formats/Png/PngEncoderTests.cs
+++ b/tests/ImageSharp.Tests/Formats/Png/PngEncoderTests.cs
@@ -407,6 +407,7 @@ public void Encode_WithTransparentColorBehaviorClear_Works(PngColorType colorTyp
     [WithFile(TestImages.Png.APng, PixelTypes.Rgba32)]
     [WithFile(TestImages.Png.DefaultNotAnimated, PixelTypes.Rgba32)]
     [WithFile(TestImages.Png.FrameOffset, PixelTypes.Rgba32)]
+    [WithFile(TestImages.Png.Issue2882, PixelTypes.Rgba32)]
     public void Encode_APng<TPixel>(TestImageProvider<TPixel> provider)
         where TPixel : unmanaged, IPixel<TPixel>
     {
diff --git a/tests/ImageSharp.Tests/TestImages.cs b/tests/ImageSharp.Tests/TestImages.cs
index abaec4997c..71dfe0480e 100644
--- a/tests/ImageSharp.Tests/TestImages.cs
+++ b/tests/ImageSharp.Tests/TestImages.cs
@@ -76,6 +76,7 @@ public static class Png
         public const string FrameOffset = "Png/animated/frame-offset.png";
         public const string DefaultNotAnimated = "Png/animated/default-not-animated.png";
         public const string Issue2666 = "Png/issues/Issue_2666.png";
+        public const string Issue2882 = "Png/issues/Issue_2882.png";
 
         // Filtered test images from http://www.schaik.com/pngsuite/pngsuite_fil_png.html
         public const string Filter0 = "Png/filter0.png";
diff --git a/tests/Images/Input/Png/issues/Issue_2882.png b/tests/Images/Input/Png/issues/Issue_2882.png
new file mode 100644
index 0000000000..2d7a51dacb
--- /dev/null
+++ b/tests/Images/Input/Png/issues/Issue_2882.png
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:cebc98e62bcfe31df73ae7b6980382f4b56bdf7e7e6e9037946f5a84cb51c7d2
+size 1117

From a84160be9f1993bc43d84faa5ec14c567e432212 Mon Sep 17 00:00:00 2001
From: James Jackson-South <james_south@hotmail.com>
Date: Thu, 27 Mar 2025 13:07:08 +1000
Subject: [PATCH 09/18] Add new benchmarks

---
 .../Quantization/QuantizerOptions.cs          |  5 +-
 .../Codecs/Gif/DecodeEncodeGif.cs             | 59 +++++++++++++++++++
 .../Codecs/Gif/EncodeGif.cs                   | 26 +++++---
 3 files changed, 80 insertions(+), 10 deletions(-)
 create mode 100644 tests/ImageSharp.Benchmarks/Codecs/Gif/DecodeEncodeGif.cs

diff --git a/src/ImageSharp/Processing/Processors/Quantization/QuantizerOptions.cs b/src/ImageSharp/Processing/Processors/Quantization/QuantizerOptions.cs
index 7a66204c64..85db2b7c4e 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/QuantizerOptions.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/QuantizerOptions.cs
@@ -10,9 +10,11 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization;
 /// </summary>
 public class QuantizerOptions
 {
+#pragma warning disable IDE0032 // Use auto property
     private float ditherScale = QuantizerConstants.MaxDitherScale;
     private int maxColors = QuantizerConstants.MaxColors;
     private float threshold = QuantizerConstants.DefaultTransparencyThreshold;
+#pragma warning restore IDE0032 // Use auto property
 
     /// <summary>
     /// Gets or sets the  algorithm to apply to the output image.
@@ -58,6 +60,7 @@ public float TransparencyThreshold
 
     /// <summary>
     /// Gets or sets the color matching mode used for matching pixel values to palette colors.
+    /// Defaults to <see cref="ColorMatchingMode.Coarse"/>.
     /// </summary>
-    public ColorMatchingMode ColorMatchingMode { get; set; } = ColorMatchingMode.Hybrid;
+    public ColorMatchingMode ColorMatchingMode { get; set; } = ColorMatchingMode.Coarse;
 }
diff --git a/tests/ImageSharp.Benchmarks/Codecs/Gif/DecodeEncodeGif.cs b/tests/ImageSharp.Benchmarks/Codecs/Gif/DecodeEncodeGif.cs
new file mode 100644
index 0000000000..3238e8dac2
--- /dev/null
+++ b/tests/ImageSharp.Benchmarks/Codecs/Gif/DecodeEncodeGif.cs
@@ -0,0 +1,59 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Drawing.Imaging;
+using BenchmarkDotNet.Attributes;
+using SixLabors.ImageSharp.Formats.Gif;
+using SixLabors.ImageSharp.Processing;
+using SixLabors.ImageSharp.Processing.Processors.Quantization;
+using SixLabors.ImageSharp.Tests;
+using SDImage = System.Drawing.Image;
+
+namespace SixLabors.ImageSharp.Benchmarks.Codecs;
+
+public abstract class DecodeEncodeGif
+{
+    private MemoryStream outputStream;
+
+    protected abstract GifEncoder Encoder { get; }
+
+    [Params(TestImages.Gif.Leo, TestImages.Gif.Cheers)]
+    public string TestImage { get; set; }
+
+    private string TestImageFullPath => Path.Combine(TestEnvironment.InputImagesDirectoryFullPath, this.TestImage);
+
+    [GlobalSetup]
+    public void Setup() => this.outputStream = new MemoryStream();
+
+    [GlobalCleanup]
+    public void Cleanup() => this.outputStream.Close();
+
+    [Benchmark(Baseline = true)]
+    public void SystemDrawing()
+    {
+        this.outputStream.Position = 0;
+        using SDImage image = SDImage.FromFile(this.TestImageFullPath);
+        image.Save(this.outputStream, ImageFormat.Gif);
+    }
+
+    [Benchmark]
+    public void ImageSharp()
+    {
+        this.outputStream.Position = 0;
+        using Image image = Image.Load(this.TestImageFullPath);
+        image.SaveAsGif(this.outputStream, this.Encoder);
+    }
+}
+
+public class DecodeEncodeGif_DefaultEncoder : DecodeEncodeGif
+{
+    protected override GifEncoder Encoder => new();
+}
+
+public class DecodeEncodeGif_CoarsePaletteEncoder : DecodeEncodeGif
+{
+    protected override GifEncoder Encoder => new()
+    {
+        Quantizer = new WebSafePaletteQuantizer(new QuantizerOptions { Dither = KnownDitherings.Bayer4x4, ColorMatchingMode = ColorMatchingMode.Coarse })
+    };
+}
diff --git a/tests/ImageSharp.Benchmarks/Codecs/Gif/EncodeGif.cs b/tests/ImageSharp.Benchmarks/Codecs/Gif/EncodeGif.cs
index beedbbe07c..2b2428210a 100644
--- a/tests/ImageSharp.Benchmarks/Codecs/Gif/EncodeGif.cs
+++ b/tests/ImageSharp.Benchmarks/Codecs/Gif/EncodeGif.cs
@@ -12,21 +12,16 @@
 
 namespace SixLabors.ImageSharp.Benchmarks.Codecs;
 
-[Config(typeof(Config.Short))]
-public class EncodeGif
+public abstract class EncodeGif
 {
     // System.Drawing needs this.
     private FileStream bmpStream;
     private SDImage bmpDrawing;
     private Image<Rgba32> bmpCore;
 
-    // Try to get as close to System.Drawing's output as possible
-    private readonly GifEncoder encoder = new()
-    {
-        Quantizer = new WebSafePaletteQuantizer(new QuantizerOptions { Dither = KnownDitherings.Bayer4x4 })
-    };
+    protected abstract GifEncoder Encoder { get; }
 
-    [Params(TestImages.Bmp.Car, TestImages.Png.Rgb48Bpp)]
+    [Params(TestImages.Gif.Leo, TestImages.Gif.Cheers)]
     public string TestImage { get; set; }
 
     [GlobalSetup]
@@ -61,6 +56,19 @@ public void GifSystemDrawing()
     public void GifImageSharp()
     {
         using MemoryStream memoryStream = new();
-        this.bmpCore.SaveAsGif(memoryStream, this.encoder);
+        this.bmpCore.SaveAsGif(memoryStream, this.Encoder);
     }
 }
+
+public class EncodeGif_DefaultEncoder : EncodeGif
+{
+    protected override GifEncoder Encoder => new();
+}
+
+public class EncodeGif_CoarsePaletteEncoder : EncodeGif
+{
+    protected override GifEncoder Encoder => new()
+    {
+        Quantizer = new WebSafePaletteQuantizer(new QuantizerOptions { Dither = KnownDitherings.Bayer4x4, ColorMatchingMode = ColorMatchingMode.Coarse })
+    };
+}

From dca98af177aa9da5e96a5c131360e53a3a7de141 Mon Sep 17 00:00:00 2001
From: James Jackson-South <james_south@hotmail.com>
Date: Thu, 27 Mar 2025 14:14:31 +1000
Subject: [PATCH 10/18] Update test ref images to match caching

---
 .../Processors/Dithering/PaletteDitherProcessor{TPixel}.cs  | 2 +-
 tests/ImageSharp.Tests/Formats/Png/PngEncoderTests.cs       | 6 +++++-
 .../Encode_8BitColor_WithOctreeQuantizer_rgb32.bmp          | 2 +-
 .../Encode_8BitColor_WithWuQuantizer_rgb32.bmp              | 2 +-
 .../ApplyDiffusionFilterInBox_Rgba32_CalliphoraPartial.png  | 4 ++--
 ...usionFilter_WorksWithAllErrorDiffusers_Bike_Atkinson.png | 4 ++--
 ...iffusionFilter_WorksWithAllErrorDiffusers_Bike_Burks.png | 4 ++--
 ...ilter_WorksWithAllErrorDiffusers_Bike_FloydSteinberg.png | 4 ++--
 ...er_WorksWithAllErrorDiffusers_Bike_JarvisJudiceNinke.png | 4 ++--
 ...fusionFilter_WorksWithAllErrorDiffusers_Bike_Sierra2.png | 4 ++--
 ...fusionFilter_WorksWithAllErrorDiffusers_Bike_Sierra3.png | 4 ++--
 ...ionFilter_WorksWithAllErrorDiffusers_Bike_SierraLite.png | 4 ++--
 ...Filter_WorksWithAllErrorDiffusers_Bike_StevensonArce.png | 4 ++--
 ...ffusionFilter_WorksWithAllErrorDiffusers_Bike_Stucki.png | 4 ++--
 ...orksWithAllErrorDiffusers_CalliphoraPartial_Atkinson.png | 4 ++--
 ...r_WorksWithAllErrorDiffusers_CalliphoraPartial_Burks.png | 4 ++--
 ...thAllErrorDiffusers_CalliphoraPartial_FloydSteinberg.png | 4 ++--
 ...llErrorDiffusers_CalliphoraPartial_JarvisJudiceNinke.png | 4 ++--
 ...WorksWithAllErrorDiffusers_CalliphoraPartial_Sierra2.png | 4 ++--
 ...WorksWithAllErrorDiffusers_CalliphoraPartial_Sierra3.png | 4 ++--
 ...ksWithAllErrorDiffusers_CalliphoraPartial_SierraLite.png | 4 ++--
 ...ithAllErrorDiffusers_CalliphoraPartial_StevensonArce.png | 4 ++--
 ..._WorksWithAllErrorDiffusers_CalliphoraPartial_Stucki.png | 4 ++--
 ...lter_ShouldNotDependOnSinglePixelType_Bgra32_filter0.png | 4 ++--
 ...ilter_ShouldNotDependOnSinglePixelType_Rgb24_filter0.png | 4 ++--
 ...lter_ShouldNotDependOnSinglePixelType_Rgba32_filter0.png | 4 ++--
 ..._ShouldNotDependOnSinglePixelType_RgbaVector_filter0.png | 4 ++--
 .../DitherFilter_WorksWithAllDitherers_Bike_Bayer16x16.png  | 4 ++--
 .../DitherFilter_WorksWithAllDitherers_Bike_Bayer2x2.png    | 4 ++--
 .../DitherFilter_WorksWithAllDitherers_Bike_Bayer4x4.png    | 4 ++--
 .../DitherFilter_WorksWithAllDitherers_Bike_Bayer8x8.png    | 4 ++--
 .../DitherFilter_WorksWithAllDitherers_Bike_Ordered3x3.png  | 4 ++--
 ...r_WorksWithAllDitherers_CalliphoraPartial_Bayer16x16.png | 4 ++--
 ...ter_WorksWithAllDitherers_CalliphoraPartial_Bayer2x2.png | 4 ++--
 ...ter_WorksWithAllDitherers_CalliphoraPartial_Bayer4x4.png | 4 ++--
 ...ter_WorksWithAllDitherers_CalliphoraPartial_Bayer8x8.png | 4 ++--
 ...r_WorksWithAllDitherers_CalliphoraPartial_Ordered3x3.png | 4 ++--
 .../00.gif                                                  | 4 ++--
 .../08.gif                                                  | 4 ++--
 .../104.gif                                                 | 4 ++--
 .../112.gif                                                 | 4 ++--
 .../16.gif                                                  | 4 ++--
 .../24.gif                                                  | 4 ++--
 .../32.gif                                                  | 4 ++--
 .../40.gif                                                  | 4 ++--
 .../48.gif                                                  | 4 ++--
 .../56.gif                                                  | 4 ++--
 .../64.gif                                                  | 4 ++--
 .../72.gif                                                  | 4 ++--
 .../80.gif                                                  | 4 ++--
 .../88.gif                                                  | 4 ++--
 .../96.gif                                                  | 4 ++--
 .../00.png                                                  | 4 ++--
 .../08.png                                                  | 4 ++--
 .../104.png                                                 | 4 ++--
 .../112.png                                                 | 4 ++--
 .../16.png                                                  | 4 ++--
 .../24.png                                                  | 4 ++--
 .../32.png                                                  | 4 ++--
 .../40.png                                                  | 4 ++--
 .../48.png                                                  | 4 ++--
 .../56.png                                                  | 4 ++--
 .../64.png                                                  | 4 ++--
 .../72.png                                                  | 4 ++--
 .../80.png                                                  | 4 ++--
 .../88.png                                                  | 4 ++--
 .../96.png                                                  | 4 ++--
 .../00.png                                                  | 4 ++--
 .../08.png                                                  | 4 ++--
 ...sue2469_Quantized_Encode_Artifacts_Rgba32_issue_2469.png | 4 ++--
 .../Issue2668_Quantized_Encode_Alpha_Rgba32_Issue_2668.png  | 4 ++--
 ...lyQuantizationInBox_Bike_OctreeQuantizer_ErrorDither.png | 4 ++--
 ...QuantizationInBox_Bike_OctreeQuantizer_OrderedDither.png | 4 ++--
 ...zationInBox_Bike_WebSafePaletteQuantizer_ErrorDither.png | 4 ++--
 ...ntizationInBox_Bike_WebSafePaletteQuantizer_NoDither.png | 4 ++--
 ...tionInBox_Bike_WebSafePaletteQuantizer_OrderedDither.png | 4 ++--
 ...izationInBox_Bike_WernerPaletteQuantizer_ErrorDither.png | 4 ++--
 ...antizationInBox_Bike_WernerPaletteQuantizer_NoDither.png | 4 ++--
 ...ationInBox_Bike_WernerPaletteQuantizer_OrderedDither.png | 4 ++--
 .../ApplyQuantizationInBox_Bike_WuQuantizer_ErrorDither.png | 4 ++--
 ...pplyQuantizationInBox_Bike_WuQuantizer_OrderedDither.png | 4 ++--
 ...nInBox_CalliphoraPartial_OctreeQuantizer_ErrorDither.png | 4 ++--
 ...nBox_CalliphoraPartial_OctreeQuantizer_OrderedDither.png | 4 ++--
 ...alliphoraPartial_WebSafePaletteQuantizer_ErrorDither.png | 4 ++--
 ...x_CalliphoraPartial_WebSafePaletteQuantizer_NoDither.png | 4 ++--
 ...liphoraPartial_WebSafePaletteQuantizer_OrderedDither.png | 4 ++--
 ...CalliphoraPartial_WernerPaletteQuantizer_ErrorDither.png | 4 ++--
 ...ox_CalliphoraPartial_WernerPaletteQuantizer_NoDither.png | 4 ++--
 ...lliphoraPartial_WernerPaletteQuantizer_OrderedDither.png | 4 ++--
 ...ationInBox_CalliphoraPartial_WuQuantizer_ErrorDither.png | 4 ++--
 ...ionInBox_CalliphoraPartial_WuQuantizer_OrderedDither.png | 4 ++--
 ...itheringScale_david_OctreeQuantizer_ErrorDither_0.25.png | 4 ++--
 ...DitheringScale_david_OctreeQuantizer_ErrorDither_0.5.png | 4 ++--
 ...itheringScale_david_OctreeQuantizer_ErrorDither_0.75.png | 4 ++--
 ...thDitheringScale_david_OctreeQuantizer_ErrorDither_0.png | 4 ++--
 ...thDitheringScale_david_OctreeQuantizer_ErrorDither_1.png | 4 ++--
 ...heringScale_david_OctreeQuantizer_OrderedDither_0.25.png | 4 ++--
 ...theringScale_david_OctreeQuantizer_OrderedDither_0.5.png | 4 ++--
 ...heringScale_david_OctreeQuantizer_OrderedDither_0.75.png | 4 ++--
 ...DitheringScale_david_OctreeQuantizer_OrderedDither_0.png | 4 ++--
 ...DitheringScale_david_OctreeQuantizer_OrderedDither_1.png | 4 ++--
 ...Scale_david_WebSafePaletteQuantizer_ErrorDither_0.25.png | 4 ++--
 ...gScale_david_WebSafePaletteQuantizer_ErrorDither_0.5.png | 4 ++--
 ...Scale_david_WebSafePaletteQuantizer_ErrorDither_0.75.png | 4 ++--
 ...ingScale_david_WebSafePaletteQuantizer_ErrorDither_0.png | 4 ++--
 ...ingScale_david_WebSafePaletteQuantizer_ErrorDither_1.png | 4 ++--
 ...ale_david_WebSafePaletteQuantizer_OrderedDither_0.25.png | 4 ++--
 ...cale_david_WebSafePaletteQuantizer_OrderedDither_0.5.png | 4 ++--
 ...ale_david_WebSafePaletteQuantizer_OrderedDither_0.75.png | 4 ++--
 ...gScale_david_WebSafePaletteQuantizer_OrderedDither_0.png | 4 ++--
 ...gScale_david_WebSafePaletteQuantizer_OrderedDither_1.png | 4 ++--
 ...gScale_david_WernerPaletteQuantizer_ErrorDither_0.25.png | 4 ++--
 ...ngScale_david_WernerPaletteQuantizer_ErrorDither_0.5.png | 4 ++--
 ...gScale_david_WernerPaletteQuantizer_ErrorDither_0.75.png | 4 ++--
 ...ringScale_david_WernerPaletteQuantizer_ErrorDither_0.png | 4 ++--
 ...ringScale_david_WernerPaletteQuantizer_ErrorDither_1.png | 4 ++--
 ...cale_david_WernerPaletteQuantizer_OrderedDither_0.25.png | 4 ++--
 ...Scale_david_WernerPaletteQuantizer_OrderedDither_0.5.png | 4 ++--
 ...cale_david_WernerPaletteQuantizer_OrderedDither_0.75.png | 4 ++--
 ...ngScale_david_WernerPaletteQuantizer_OrderedDither_0.png | 4 ++--
 ...ngScale_david_WernerPaletteQuantizer_OrderedDither_1.png | 4 ++--
 ...WithDitheringScale_david_WuQuantizer_ErrorDither_0.5.png | 4 ++--
 ...ithDitheringScale_david_WuQuantizer_ErrorDither_0.75.png | 4 ++--
 ...onWithDitheringScale_david_WuQuantizer_ErrorDither_1.png | 4 ++--
 ...hDitheringScale_david_WuQuantizer_OrderedDither_0.25.png | 4 ++--
 ...thDitheringScale_david_WuQuantizer_OrderedDither_0.5.png | 4 ++--
 ...hDitheringScale_david_WuQuantizer_OrderedDither_0.75.png | 4 ++--
 ...WithDitheringScale_david_WuQuantizer_OrderedDither_1.png | 4 ++--
 .../ApplyQuantization_Bike_OctreeQuantizer_ErrorDither.png  | 4 ++--
 ...ApplyQuantization_Bike_OctreeQuantizer_OrderedDither.png | 4 ++--
 ...uantization_Bike_WebSafePaletteQuantizer_ErrorDither.png | 4 ++--
 ...lyQuantization_Bike_WebSafePaletteQuantizer_NoDither.png | 4 ++--
 ...ntization_Bike_WebSafePaletteQuantizer_OrderedDither.png | 4 ++--
 ...Quantization_Bike_WernerPaletteQuantizer_ErrorDither.png | 4 ++--
 ...plyQuantization_Bike_WernerPaletteQuantizer_NoDither.png | 4 ++--
 ...antization_Bike_WernerPaletteQuantizer_OrderedDither.png | 4 ++--
 .../ApplyQuantization_Bike_WuQuantizer_ErrorDither.png      | 4 ++--
 .../ApplyQuantization_Bike_WuQuantizer_OrderedDither.png    | 4 ++--
 ...zation_CalliphoraPartial_OctreeQuantizer_ErrorDither.png | 4 ++--
 ...tion_CalliphoraPartial_OctreeQuantizer_OrderedDither.png | 4 ++--
 ...alliphoraPartial_WebSafePaletteQuantizer_ErrorDither.png | 4 ++--
 ...n_CalliphoraPartial_WebSafePaletteQuantizer_NoDither.png | 4 ++--
 ...liphoraPartial_WebSafePaletteQuantizer_OrderedDither.png | 4 ++--
 ...CalliphoraPartial_WernerPaletteQuantizer_ErrorDither.png | 4 ++--
 ...on_CalliphoraPartial_WernerPaletteQuantizer_NoDither.png | 4 ++--
 ...lliphoraPartial_WernerPaletteQuantizer_OrderedDither.png | 4 ++--
 ...antization_CalliphoraPartial_WuQuantizer_ErrorDither.png | 4 ++--
 ...tization_CalliphoraPartial_WuQuantizer_OrderedDither.png | 4 ++--
 148 files changed, 296 insertions(+), 292 deletions(-)

diff --git a/src/ImageSharp/Processing/Processors/Dithering/PaletteDitherProcessor{TPixel}.cs b/src/ImageSharp/Processing/Processors/Dithering/PaletteDitherProcessor{TPixel}.cs
index bb9b4d8c8f..0d4680e21f 100644
--- a/src/ImageSharp/Processing/Processors/Dithering/PaletteDitherProcessor{TPixel}.cs
+++ b/src/ImageSharp/Processing/Processors/Dithering/PaletteDitherProcessor{TPixel}.cs
@@ -89,7 +89,7 @@ public DitherProcessor(
             float ditherScale)
         {
             this.Configuration = configuration;
-            this.pixelMap = PixelMapFactory.Create(configuration, palette, ColorMatchingMode.Hybrid);
+            this.pixelMap = PixelMapFactory.Create(configuration, palette, ColorMatchingMode.Coarse);
             this.Palette = palette;
             this.DitherScale = ditherScale;
         }
diff --git a/tests/ImageSharp.Tests/Formats/Png/PngEncoderTests.cs b/tests/ImageSharp.Tests/Formats/Png/PngEncoderTests.cs
index 9d29b3bad5..b0d0563ccb 100644
--- a/tests/ImageSharp.Tests/Formats/Png/PngEncoderTests.cs
+++ b/tests/ImageSharp.Tests/Formats/Png/PngEncoderTests.cs
@@ -678,12 +678,16 @@ public void Issue_2862()
             }
         }
 
+        PaletteQuantizer quantizer = new(
+            palette.Select(Color.FromPixel).ToArray(),
+            new QuantizerOptions() { ColorMatchingMode = ColorMatchingMode.Hybrid });
+
         using MemoryStream ms = new();
         image.Save(ms, new PngEncoder
         {
             ColorType = PngColorType.Palette,
             BitDepth = PngBitDepth.Bit8,
-            Quantizer = new PaletteQuantizer(palette.Select(Color.FromPixel).ToArray())
+            Quantizer = quantizer
         });
 
         ms.Position = 0;
diff --git a/tests/Images/External/ReferenceOutput/BmpEncoderTests/Encode_8BitColor_WithOctreeQuantizer_rgb32.bmp b/tests/Images/External/ReferenceOutput/BmpEncoderTests/Encode_8BitColor_WithOctreeQuantizer_rgb32.bmp
index 291739dfa9..f4ae3b9b68 100644
--- a/tests/Images/External/ReferenceOutput/BmpEncoderTests/Encode_8BitColor_WithOctreeQuantizer_rgb32.bmp
+++ b/tests/Images/External/ReferenceOutput/BmpEncoderTests/Encode_8BitColor_WithOctreeQuantizer_rgb32.bmp
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:9d7441b03c24acb887b2d9a6e2346bb23e2d38293c3df3ff489d48593f87b29a
+oid sha256:a98b1ec707af066f77fad7d1a64b858d460986beb6d27682717dd5e221310fd4
 size 9270
diff --git a/tests/Images/External/ReferenceOutput/BmpEncoderTests/Encode_8BitColor_WithWuQuantizer_rgb32.bmp b/tests/Images/External/ReferenceOutput/BmpEncoderTests/Encode_8BitColor_WithWuQuantizer_rgb32.bmp
index c69ed3130c..f7eb06c558 100644
--- a/tests/Images/External/ReferenceOutput/BmpEncoderTests/Encode_8BitColor_WithWuQuantizer_rgb32.bmp
+++ b/tests/Images/External/ReferenceOutput/BmpEncoderTests/Encode_8BitColor_WithWuQuantizer_rgb32.bmp
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:5d9f2745de2b6e7fc3b1403fe651f3bbba835c67a6fb410fc8a9d91a15b44328
+oid sha256:e063e97cd8a000de6830adcc3961a7dc41785d40cd4d83af10ca38d96e071362
 size 9270
diff --git a/tests/Images/External/ReferenceOutput/DitherTests/ApplyDiffusionFilterInBox_Rgba32_CalliphoraPartial.png b/tests/Images/External/ReferenceOutput/DitherTests/ApplyDiffusionFilterInBox_Rgba32_CalliphoraPartial.png
index 401ceaa36c..de42d1bfc2 100644
--- a/tests/Images/External/ReferenceOutput/DitherTests/ApplyDiffusionFilterInBox_Rgba32_CalliphoraPartial.png
+++ b/tests/Images/External/ReferenceOutput/DitherTests/ApplyDiffusionFilterInBox_Rgba32_CalliphoraPartial.png
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:596472e74050d968479b672c1d2436b179e41a7b99fcefb53286ad47e5a4fe13
-size 273115
+oid sha256:681b0e36298cb702683fb9ffb2a82f7dfd9080b268db19a03f413809f69d0e07
+size 273269
diff --git a/tests/Images/External/ReferenceOutput/DitherTests/DiffusionFilter_WorksWithAllErrorDiffusers_Bike_Atkinson.png b/tests/Images/External/ReferenceOutput/DitherTests/DiffusionFilter_WorksWithAllErrorDiffusers_Bike_Atkinson.png
index 0b03e4e185..1656b2e9cb 100644
--- a/tests/Images/External/ReferenceOutput/DitherTests/DiffusionFilter_WorksWithAllErrorDiffusers_Bike_Atkinson.png
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diff --git a/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_Bike_WebSafePaletteQuantizer_OrderedDither.png b/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_Bike_WebSafePaletteQuantizer_OrderedDither.png
index c9ad188dc1..2a3e95c169 100644
--- a/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_Bike_WebSafePaletteQuantizer_OrderedDither.png
+++ b/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_Bike_WebSafePaletteQuantizer_OrderedDither.png
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diff --git a/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_Bike_WernerPaletteQuantizer_ErrorDither.png b/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_Bike_WernerPaletteQuantizer_ErrorDither.png
index 7cfe595a16..96c66aad72 100644
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+++ b/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_Bike_WernerPaletteQuantizer_ErrorDither.png
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diff --git a/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_Bike_WernerPaletteQuantizer_NoDither.png b/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_Bike_WernerPaletteQuantizer_NoDither.png
index ff91ab181f..3ff151f6d0 100644
--- a/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_Bike_WernerPaletteQuantizer_NoDither.png
+++ b/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_Bike_WernerPaletteQuantizer_NoDither.png
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diff --git a/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_Bike_WernerPaletteQuantizer_OrderedDither.png b/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_Bike_WernerPaletteQuantizer_OrderedDither.png
index 987f01d0a3..ddb32d1f1f 100644
--- a/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_Bike_WernerPaletteQuantizer_OrderedDither.png
+++ b/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_Bike_WernerPaletteQuantizer_OrderedDither.png
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diff --git a/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_Bike_WuQuantizer_ErrorDither.png b/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_Bike_WuQuantizer_ErrorDither.png
index 5860c0eacc..37e5035d86 100644
--- a/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_Bike_WuQuantizer_ErrorDither.png
+++ b/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_Bike_WuQuantizer_ErrorDither.png
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diff --git a/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_Bike_WuQuantizer_OrderedDither.png b/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_Bike_WuQuantizer_OrderedDither.png
index deda6d6db8..6004ca95f0 100644
--- a/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_Bike_WuQuantizer_OrderedDither.png
+++ b/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_Bike_WuQuantizer_OrderedDither.png
@@ -1,3 +1,3 @@
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diff --git a/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_OctreeQuantizer_ErrorDither.png b/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_OctreeQuantizer_ErrorDither.png
index 34a6c57902..314a056060 100644
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+++ b/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_OctreeQuantizer_ErrorDither.png
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diff --git a/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_OctreeQuantizer_OrderedDither.png b/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_OctreeQuantizer_OrderedDither.png
index 0f56d5156c..1ba333247c 100644
--- a/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_OctreeQuantizer_OrderedDither.png
+++ b/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_OctreeQuantizer_OrderedDither.png
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diff --git a/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_WebSafePaletteQuantizer_ErrorDither.png b/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_WebSafePaletteQuantizer_ErrorDither.png
index 2d6226d096..a14c2cb1f6 100644
--- a/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_WebSafePaletteQuantizer_ErrorDither.png
+++ b/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_WebSafePaletteQuantizer_ErrorDither.png
@@ -1,3 +1,3 @@
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+size 60688
diff --git a/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_WebSafePaletteQuantizer_NoDither.png b/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_WebSafePaletteQuantizer_NoDither.png
index 7b842e1f78..e40a91cbc4 100644
--- a/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_WebSafePaletteQuantizer_NoDither.png
+++ b/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_WebSafePaletteQuantizer_NoDither.png
@@ -1,3 +1,3 @@
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diff --git a/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_WebSafePaletteQuantizer_OrderedDither.png b/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_WebSafePaletteQuantizer_OrderedDither.png
index bf0604356f..84d641f271 100644
--- a/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_WebSafePaletteQuantizer_OrderedDither.png
+++ b/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_WebSafePaletteQuantizer_OrderedDither.png
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diff --git a/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_WernerPaletteQuantizer_ErrorDither.png b/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_WernerPaletteQuantizer_ErrorDither.png
index fd27271129..0d548ca79d 100644
--- a/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_WernerPaletteQuantizer_ErrorDither.png
+++ b/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_WernerPaletteQuantizer_ErrorDither.png
@@ -1,3 +1,3 @@
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diff --git a/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_WernerPaletteQuantizer_NoDither.png b/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_WernerPaletteQuantizer_NoDither.png
index 2bad1f1f25..8d0d2b60db 100644
--- a/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_WernerPaletteQuantizer_NoDither.png
+++ b/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_WernerPaletteQuantizer_NoDither.png
@@ -1,3 +1,3 @@
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diff --git a/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_WernerPaletteQuantizer_OrderedDither.png b/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_WernerPaletteQuantizer_OrderedDither.png
index f8962d9907..53699affb6 100644
--- a/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_WernerPaletteQuantizer_OrderedDither.png
+++ b/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_WernerPaletteQuantizer_OrderedDither.png
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diff --git a/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_WuQuantizer_ErrorDither.png b/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_WuQuantizer_ErrorDither.png
index d8a04a055d..7204abff47 100644
--- a/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_WuQuantizer_ErrorDither.png
+++ b/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_WuQuantizer_ErrorDither.png
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diff --git a/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_WuQuantizer_OrderedDither.png b/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_WuQuantizer_OrderedDither.png
index 6b11fd3ead..c1056c0ce8 100644
--- a/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_WuQuantizer_OrderedDither.png
+++ b/tests/Images/External/ReferenceOutput/QuantizerTests/ApplyQuantization_CalliphoraPartial_WuQuantizer_OrderedDither.png
@@ -1,3 +1,3 @@
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From 32da5cdd8263566ed7139213032e43fa6868e7b9 Mon Sep 17 00:00:00 2001
From: James Jackson-South <james_south@hotmail.com>
Date: Thu, 27 Mar 2025 23:04:24 +1000
Subject: [PATCH 11/18] Fix build, simplify utilities

---
 Directory.Build.props                         |  5 +-
 src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs  |  2 +-
 src/ImageSharp/Formats/EncodingUtilities.cs   | 52 ++++++-------------
 src/ImageSharp/Formats/Gif/GifEncoderCore.cs  |  8 ++-
 src/ImageSharp/Formats/Png/PngDecoderCore.cs  |  4 +-
 src/ImageSharp/Formats/Png/PngEncoderCore.cs  |  4 +-
 src/ImageSharp/Formats/Qoi/QoiEncoderCore.cs  |  4 +-
 src/ImageSharp/Formats/Tga/TgaEncoderCore.cs  |  4 +-
 .../Formats/Tiff/TiffEncoderCore.cs           |  4 +-
 .../Formats/TransparentColorMode.cs           |  2 +-
 src/ImageSharp/IDeepCloneable.cs              |  6 +--
 .../Quantization/OctreeQuantizer{TPixel}.cs   | 21 ++------
 .../Quantization/PaletteQuantizer{TPixel}.cs  |  1 +
 .../Quantization/QuantizerOptions.cs          | 43 +++++++++++----
 .../Quantization/QuantizerUtilities.cs        | 49 ++++++++---------
 .../Quantization/WuQuantizer{TPixel}.cs       | 13 +----
 16 files changed, 104 insertions(+), 118 deletions(-)

diff --git a/Directory.Build.props b/Directory.Build.props
index 26b3cc5afc..1191e848ef 100644
--- a/Directory.Build.props
+++ b/Directory.Build.props
@@ -21,9 +21,8 @@
   <!-- Import the shared global .props file -->
   <Import Project="$(MSBuildThisFileDirectory)shared-infrastructure\msbuild\props\SixLabors.Global.props" />
 
-  <PropertyGroup Condition="$(SIXLABORS_TESTING_PREVIEW) == true">
-    <!-- Workaround various issues bound to implicit language features. -->
-    <LangVersion>preview</LangVersion>
+  <PropertyGroup>
+    <LangVersion>13.0</LangVersion>
   </PropertyGroup>
 
   <!--
diff --git a/src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs b/src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs
index 6a88f080d9..46da463455 100644
--- a/src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs
+++ b/src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs
@@ -368,7 +368,7 @@ private void WriteImage<TPixel>(
             if (bpp > 8 && EncodingUtilities.ShouldReplaceTransparentPixels<TPixel>(this.transparentColorMode))
             {
                 clonedFrame = image.Frames.RootFrame.Clone();
-                EncodingUtilities.ReplaceTransparentPixels(clonedFrame, Color.Transparent);
+                EncodingUtilities.ReplaceTransparentPixels(clonedFrame);
             }
 
             ImageFrame<TPixel> encodingFrame = clonedFrame ?? image.Frames.RootFrame;
diff --git a/src/ImageSharp/Formats/EncodingUtilities.cs b/src/ImageSharp/Formats/EncodingUtilities.cs
index 130dd567eb..3994743933 100644
--- a/src/ImageSharp/Formats/EncodingUtilities.cs
+++ b/src/ImageSharp/Formats/EncodingUtilities.cs
@@ -27,71 +27,58 @@ public static bool ShouldReplaceTransparentPixels<TPixel>(TransparentColorMode m
         => mode == TransparentColorMode.Clear && TPixel.GetPixelTypeInfo().AlphaRepresentation == PixelAlphaRepresentation.Unassociated;
 
     /// <summary>
-    /// Replaces transparent pixels with pixels represented by <paramref name="color"/>.
+    /// Replaces pixels with a transparent alpha component with fully transparent pixels.
     /// </summary>
     /// <typeparam name="TPixel">The type of the pixel.</typeparam>
     /// <param name="frame">The <see cref="ImageFrame{TPixel}"/> where the transparent pixels will be changed.</param>
-    /// <param name="color">The color to replace transparent pixels with.</param>
-    public static void ReplaceTransparentPixels<TPixel>(ImageFrame<TPixel> frame, Color color)
+    public static void ReplaceTransparentPixels<TPixel>(ImageFrame<TPixel> frame)
         where TPixel : unmanaged, IPixel<TPixel>
-        => ReplaceTransparentPixels(frame.Configuration, frame.PixelBuffer, color);
+        => ReplaceTransparentPixels(frame.Configuration, frame.PixelBuffer);
 
     /// <summary>
-    /// Replaces transparent pixels with pixels represented by <paramref name="color"/>.
+    /// Replaces pixels with a transparent alpha component with fully transparent pixels.
     /// </summary>
     /// <typeparam name="TPixel">The type of the pixel.</typeparam>
     /// <param name="configuration">The configuration.</param>
     /// <param name="buffer">The  <see cref="Buffer2D{TPixel}"/> where the transparent pixels will be changed.</param>
-    /// <param name="color">The color to replace transparent pixels with.</param>
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public static void ReplaceTransparentPixels<TPixel>(
-        Configuration configuration,
-        Buffer2D<TPixel> buffer,
-        Color color)
+    public static void ReplaceTransparentPixels<TPixel>(Configuration configuration, Buffer2D<TPixel> buffer)
         where TPixel : unmanaged, IPixel<TPixel>
     {
         Buffer2DRegion<TPixel> region = buffer.GetRegion();
-        ReplaceTransparentPixels(configuration, in region, color);
+        ReplaceTransparentPixels(configuration, in region);
     }
 
     /// <summary>
-    /// Replaces transparent pixels with pixels represented by <paramref name="color"/>.
+    /// Replaces pixels with a transparent alpha component with fully transparent pixels.
     /// </summary>
     /// <typeparam name="TPixel">The type of the pixel.</typeparam>
     /// <param name="configuration">The configuration.</param>
     /// <param name="region">The <see cref="Buffer2DRegion{T}"/> where the transparent pixels will be changed.</param>
-    /// <param name="color">The color to replace transparent pixels with.</param>
     public static void ReplaceTransparentPixels<TPixel>(
         Configuration configuration,
-        in Buffer2DRegion<TPixel> region,
-        Color color)
+        in Buffer2DRegion<TPixel> region)
         where TPixel : unmanaged, IPixel<TPixel>
     {
         using IMemoryOwner<Vector4> vectors = configuration.MemoryAllocator.Allocate<Vector4>(region.Width);
         Span<Vector4> vectorsSpan = vectors.GetSpan();
-        Vector4 replacement = color.ToScaledVector4();
         for (int y = 0; y < region.Height; y++)
         {
             Span<TPixel> span = region.DangerousGetRowSpan(y);
             PixelOperations<TPixel>.Instance.ToVector4(configuration, span, vectorsSpan, PixelConversionModifiers.Scale);
-            ReplaceTransparentPixels(vectorsSpan, replacement);
+            ReplaceTransparentPixels(vectorsSpan);
             PixelOperations<TPixel>.Instance.FromVector4Destructive(configuration, vectorsSpan, span, PixelConversionModifiers.Scale);
         }
     }
 
     /// <summary>
-    /// Replaces transparent pixels with pixels represented by <paramref name="replacement"/>.
+    /// Replaces pixels with a transparent alpha component with fully transparent pixels.
     /// </summary>
     /// <param name="source">A span of color vectors that will be checked for transparency and potentially modified.</param>
-    /// <param name="replacement">A color vector that will replace transparent pixels when the alpha value is below the specified threshold.</param>
-    public static void ReplaceTransparentPixels(Span<Vector4> source, Vector4 replacement)
+    public static void ReplaceTransparentPixels(Span<Vector4> source)
     {
         if (Vector512.IsHardwareAccelerated && source.Length >= 4)
         {
-            Vector128<float> replacement128 = replacement.AsVector128();
-            Vector256<float> replacement256 = Vector256.Create(replacement128, replacement128);
-            Vector512<float> replacement512 = Vector512.Create(replacement256, replacement256);
-
             Span<Vector512<float>> source512 = MemoryMarshal.Cast<Vector4, Vector512<float>>(source);
             for (int i = 0; i < source512.Length; i++)
             {
@@ -105,7 +92,7 @@ public static void ReplaceTransparentPixels(Span<Vector4> source, Vector4 replac
 
                 // Use the mask to select the replacement vector
                 // (replacement & mask) | (v512 & ~mask)
-                v = Vector512.ConditionalSelect(mask, replacement512, v);
+                v = Vector512.ConditionalSelect(mask, Vector512<float>.Zero, v);
             }
 
             int m = Numerics.Modulo4(source.Length);
@@ -115,16 +102,13 @@ public static void ReplaceTransparentPixels(Span<Vector4> source, Vector4 replac
                 {
                     if (source[i].W == 0)
                     {
-                        source[i] = replacement;
+                        source[i] = Vector4.Zero;
                     }
                 }
             }
         }
         else if (Vector256.IsHardwareAccelerated && source.Length >= 2)
         {
-            Vector128<float> replacement128 = replacement.AsVector128();
-            Vector256<float> replacement256 = Vector256.Create(replacement128, replacement128);
-
             Span<Vector256<float>> source256 = MemoryMarshal.Cast<Vector4, Vector256<float>>(source);
             for (int i = 0; i < source256.Length; i++)
             {
@@ -138,7 +122,7 @@ public static void ReplaceTransparentPixels(Span<Vector4> source, Vector4 replac
 
                 // Use the mask to select the replacement vector
                 // (replacement & mask) | (v256 & ~mask)
-                v = Vector256.ConditionalSelect(mask, replacement256, v);
+                v = Vector256.ConditionalSelect(mask, Vector256<float>.Zero, v);
             }
 
             int m = Numerics.Modulo2(source.Length);
@@ -148,15 +132,13 @@ public static void ReplaceTransparentPixels(Span<Vector4> source, Vector4 replac
                 {
                     if (source[i].W == 0)
                     {
-                        source[i] = replacement;
+                        source[i] = Vector4.Zero;
                     }
                 }
             }
         }
         else if (Vector128.IsHardwareAccelerated)
         {
-            Vector128<float> replacement128 = replacement.AsVector128();
-
             for (int i = 0; i < source.Length; i++)
             {
                 ref Vector4 v = ref source[i];
@@ -170,7 +152,7 @@ public static void ReplaceTransparentPixels(Span<Vector4> source, Vector4 replac
 
                 // Use the mask to select the replacement vector
                 // (replacement & mask) | (v128 & ~mask)
-                v = Vector128.ConditionalSelect(mask, replacement128, v128).AsVector4();
+                v = Vector128.ConditionalSelect(mask, Vector128<float>.Zero, v128).AsVector4();
             }
         }
         else
@@ -179,7 +161,7 @@ public static void ReplaceTransparentPixels(Span<Vector4> source, Vector4 replac
             {
                 if (source[i].W == 0F)
                 {
-                    source[i] = replacement;
+                    source[i] = Vector4.Zero;
                 }
             }
         }
diff --git a/src/ImageSharp/Formats/Gif/GifEncoderCore.cs b/src/ImageSharp/Formats/Gif/GifEncoderCore.cs
index eff33f2d1c..114cb4347f 100644
--- a/src/ImageSharp/Formats/Gif/GifEncoderCore.cs
+++ b/src/ImageSharp/Formats/Gif/GifEncoderCore.cs
@@ -146,12 +146,16 @@ public void Encode<TPixel>(Image<TPixel> image, Stream stream, CancellationToken
             }
         }
 
+        // Create a new quantizer options instance augmenting the transparent color mode to match the encoder.
+        TransparentColorMode mode = this.transparentColorMode;
+        QuantizerOptions options = this.quantizer.Options.DeepClone(o => o.TransparentColorMode = mode);
+
         // Quantize the first frame. Checking to see whether we can clear the transparent pixels
         // to allow for a smaller color palette and encoded result.
+        // TODO: What should we use as the background color here?
         Color background = Color.Transparent;
-        using (IQuantizer<TPixel> frameQuantizer = this.quantizer.CreatePixelSpecificQuantizer<TPixel>(this.configuration))
+        using (IQuantizer<TPixel> frameQuantizer = this.quantizer.CreatePixelSpecificQuantizer<TPixel>(this.configuration, options))
         {
-            TransparentColorMode mode = this.transparentColorMode;
             IPixelSamplingStrategy strategy = this.pixelSamplingStrategy;
 
             ImageFrame<TPixel> encodingFrame = image.Frames.RootFrame;
diff --git a/src/ImageSharp/Formats/Png/PngDecoderCore.cs b/src/ImageSharp/Formats/Png/PngDecoderCore.cs
index 9df6f14bf7..b0ec73d2a1 100644
--- a/src/ImageSharp/Formats/Png/PngDecoderCore.cs
+++ b/src/ImageSharp/Formats/Png/PngDecoderCore.cs
@@ -1086,7 +1086,7 @@ private void ProcessDefilteredScanline<TPixel>(
             {
                 PixelBlender<TPixel> blender =
                     PixelOperations<TPixel>.Instance.GetPixelBlender(PixelColorBlendingMode.Normal, PixelAlphaCompositionMode.SrcOver);
-                blender.Blend(this.configuration, destination, destination, rowSpan, 1f);
+                blender.Blend<TPixel>(this.configuration, destination, destination, rowSpan, 1F);
             }
         }
         finally
@@ -1208,7 +1208,7 @@ private void ProcessInterlacedDefilteredScanline<TPixel>(
             {
                 PixelBlender<TPixel> blender =
                     PixelOperations<TPixel>.Instance.GetPixelBlender(PixelColorBlendingMode.Normal, PixelAlphaCompositionMode.SrcOver);
-                blender.Blend(this.configuration, destination, destination, rowSpan, 1F);
+                blender.Blend<TPixel>(this.configuration, destination, destination, rowSpan, 1F);
             }
         }
         finally
diff --git a/src/ImageSharp/Formats/Png/PngEncoderCore.cs b/src/ImageSharp/Formats/Png/PngEncoderCore.cs
index 6eecff8eda..07be36ae27 100644
--- a/src/ImageSharp/Formats/Png/PngEncoderCore.cs
+++ b/src/ImageSharp/Formats/Png/PngEncoderCore.cs
@@ -197,7 +197,7 @@ public void Encode<TPixel>(Image<TPixel> image, Stream stream, CancellationToken
             {
                 currentFrame = clonedFrame = currentFrame.Clone();
                 currentFrameRegion = currentFrame.PixelBuffer.GetRegion();
-                EncodingUtilities.ReplaceTransparentPixels(this.configuration, in currentFrameRegion, this.backgroundColor.Value);
+                EncodingUtilities.ReplaceTransparentPixels(this.configuration, in currentFrameRegion);
             }
 
             // Do not move this. We require an accurate bit depth for the header chunk.
@@ -316,7 +316,7 @@ public void Encode<TPixel>(Image<TPixel> image, Stream stream, CancellationToken
 
                     if (clearTransparency && this.colorType is not PngColorType.Palette)
                     {
-                        EncodingUtilities.ReplaceTransparentPixels(encodingFrame, background);
+                        EncodingUtilities.ReplaceTransparentPixels(encodingFrame);
                     }
 
                     // Each frame control sequence number must be incremented by the number of frame data chunks that follow.
diff --git a/src/ImageSharp/Formats/Qoi/QoiEncoderCore.cs b/src/ImageSharp/Formats/Qoi/QoiEncoderCore.cs
index 916830273a..a5e1596b37 100644
--- a/src/ImageSharp/Formats/Qoi/QoiEncoderCore.cs
+++ b/src/ImageSharp/Formats/Qoi/QoiEncoderCore.cs
@@ -90,10 +90,12 @@ private void WritePixels<TPixel>(Image<TPixel> image, Stream stream, Cancellatio
         ImageFrame<TPixel>? clonedFrame = null;
         try
         {
+            // TODO: Try to avoid cloning the frame if possible.
+            // We should be cloning individual scanlines instead.
             if (EncodingUtilities.ShouldReplaceTransparentPixels<TPixel>(this.encoder.TransparentColorMode))
             {
                 clonedFrame = image.Frames.RootFrame.Clone();
-                EncodingUtilities.ReplaceTransparentPixels(clonedFrame, Color.Transparent);
+                EncodingUtilities.ReplaceTransparentPixels(clonedFrame);
             }
 
             ImageFrame<TPixel> encodingFrame = clonedFrame ?? image.Frames.RootFrame;
diff --git a/src/ImageSharp/Formats/Tga/TgaEncoderCore.cs b/src/ImageSharp/Formats/Tga/TgaEncoderCore.cs
index 17259629ae..a587e19608 100644
--- a/src/ImageSharp/Formats/Tga/TgaEncoderCore.cs
+++ b/src/ImageSharp/Formats/Tga/TgaEncoderCore.cs
@@ -110,10 +110,12 @@ public void Encode<TPixel>(Image<TPixel> image, Stream stream, CancellationToken
         ImageFrame<TPixel>? clonedFrame = null;
         try
         {
+            // TODO: Try to avoid cloning the frame if possible.
+            // We should be cloning individual scanlines instead.
             if (EncodingUtilities.ShouldReplaceTransparentPixels<TPixel>(this.transparentColorMode))
             {
                 clonedFrame = image.Frames.RootFrame.Clone();
-                EncodingUtilities.ReplaceTransparentPixels(clonedFrame, Color.Transparent);
+                EncodingUtilities.ReplaceTransparentPixels(clonedFrame);
             }
 
             ImageFrame<TPixel> encodingFrame = clonedFrame ?? image.Frames.RootFrame;
diff --git a/src/ImageSharp/Formats/Tiff/TiffEncoderCore.cs b/src/ImageSharp/Formats/Tiff/TiffEncoderCore.cs
index 1e12781a99..04cbea34da 100644
--- a/src/ImageSharp/Formats/Tiff/TiffEncoderCore.cs
+++ b/src/ImageSharp/Formats/Tiff/TiffEncoderCore.cs
@@ -146,10 +146,12 @@ public void Encode<TPixel>(Image<TPixel> image, Stream stream, CancellationToken
             {
                 cancellationToken.ThrowIfCancellationRequested();
 
+                // TODO: Try to avoid cloning the frame if possible.
+                // We should be cloning individual scanlines instead.
                 if (EncodingUtilities.ShouldReplaceTransparentPixels<TPixel>(this.transparentColorMode))
                 {
                     clonedFrame = frame.Clone();
-                    EncodingUtilities.ReplaceTransparentPixels(clonedFrame, Color.Transparent);
+                    EncodingUtilities.ReplaceTransparentPixels(clonedFrame);
                 }
 
                 ImageFrame<TPixel> encodingFrame = clonedFrame ?? frame;
diff --git a/src/ImageSharp/Formats/TransparentColorMode.cs b/src/ImageSharp/Formats/TransparentColorMode.cs
index 5b52e5fa76..c4d9c927e6 100644
--- a/src/ImageSharp/Formats/TransparentColorMode.cs
+++ b/src/ImageSharp/Formats/TransparentColorMode.cs
@@ -4,7 +4,7 @@
 namespace SixLabors.ImageSharp.Formats;
 
 /// <summary>
-/// Specifies how transparent pixels should be handled during encoding.
+/// Specifies how transparent pixels should be handled during encoding and quantization.
 /// </summary>
 public enum TransparentColorMode
 {
diff --git a/src/ImageSharp/IDeepCloneable.cs b/src/ImageSharp/IDeepCloneable.cs
index 3d00d627e0..8b225da0c7 100644
--- a/src/ImageSharp/IDeepCloneable.cs
+++ b/src/ImageSharp/IDeepCloneable.cs
@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors.
+// Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
 namespace SixLabors.ImageSharp;
@@ -14,7 +14,7 @@ public interface IDeepCloneable<out T>
     /// Creates a new <typeparamref name="T"/> that is a deep copy of the current instance.
     /// </summary>
     /// <returns>The <typeparamref name="T"/>.</returns>
-    T DeepClone();
+    public T DeepClone();
 }
 
 /// <summary>
@@ -26,5 +26,5 @@ public interface IDeepCloneable
     /// Creates a new object that is a deep copy of the current instance.
     /// </summary>
     /// <returns>The <see cref="IDeepCloneable"/>.</returns>
-    IDeepCloneable DeepClone();
+    public IDeepCloneable DeepClone();
 }
diff --git a/src/ImageSharp/Processing/Processors/Quantization/OctreeQuantizer{TPixel}.cs b/src/ImageSharp/Processing/Processors/Quantization/OctreeQuantizer{TPixel}.cs
index e094b18964..5f55a4410f 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/OctreeQuantizer{TPixel}.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/OctreeQuantizer{TPixel}.cs
@@ -45,7 +45,7 @@ public OctreeQuantizer(Configuration configuration, QuantizerOptions options)
 
         this.maxColors = this.Options.MaxColors;
         this.bitDepth = Numerics.Clamp(ColorNumerics.GetBitsNeededForColorDepth(this.maxColors), 1, 8);
-        this.octree = new Octree(configuration, this.bitDepth, this.maxColors, this.Options.TransparencyThreshold, this.Options.ThresholdReplacementColor);
+        this.octree = new Octree(configuration, this.bitDepth, this.maxColors, this.Options.TransparencyThreshold);
         this.paletteOwner = configuration.MemoryAllocator.Allocate<TPixel>(this.maxColors, AllocationOptions.Clean);
         this.pixelMap = default;
         this.palette = default;
@@ -194,11 +194,6 @@ internal sealed class Octree : IDisposable
         private int previousNode;
         private Rgba32 previousColor;
 
-        // The color to use for pixels below the transparency threshold.
-        private Vector4 thresholdReplacementColor;
-        private Vector4 thresholdReplacementColorV4;
-        private readonly Rgba32 thresholdReplacementColorRgba;
-
         // Free list for reclaimed node indices.
         private readonly Stack<short> freeIndices = new();
 
@@ -209,20 +204,15 @@ internal sealed class Octree : IDisposable
         /// <param name="maxColorBits">The maximum number of significant bits in the image.</param>
         /// <param name="maxColors">The maximum number of colors to allow in the palette.</param>
         /// <param name="transparencyThreshold">The threshold for transparent colors.</param>
-        /// <param name="thresholdReplacementColor">The color to use for pixels below the transparency threshold.</param>
         public Octree(
             Configuration configuration,
             int maxColorBits,
             int maxColors,
-            float transparencyThreshold,
-            Color thresholdReplacementColor)
+            float transparencyThreshold)
         {
             this.maxColorBits = maxColorBits;
             this.maxColors = maxColors;
             this.transparencyThreshold255 = (int)(transparencyThreshold * 255F);
-            this.thresholdReplacementColor = thresholdReplacementColor.ToScaledVector4();
-            this.thresholdReplacementColorV4 = this.thresholdReplacementColor * 255F;
-            this.thresholdReplacementColorRgba = thresholdReplacementColor.ToPixel<Rgba32>();
             this.Leaves = 0;
             this.previousNode = -1;
             this.previousColor = default;
@@ -573,7 +563,7 @@ public void ConstructPalette(Octree octree, Span<TPixel> palette, ref short pale
 
                     if (vector.W < octree.transparencyThreshold255)
                     {
-                        vector = octree.thresholdReplacementColorV4;
+                        vector = Vector4.Zero;
                     }
 
                     palette[paletteIndex] = TPixel.FromRgba32(new Rgba32((byte)vector.X, (byte)vector.Y, (byte)vector.Z, (byte)vector.W));
@@ -602,11 +592,6 @@ public void ConstructPalette(Octree octree, Span<TPixel> palette, ref short pale
             /// <param name="octree">The parent octree.</param>
             public int GetPaletteIndex(Rgba32 color, int level, Octree octree)
             {
-                if (color.A < octree.transparencyThreshold255)
-                {
-                    color = octree.thresholdReplacementColorRgba;
-                }
-
                 if (this.Leaf)
                 {
                     return this.PaletteIndex;
diff --git a/src/ImageSharp/Processing/Processors/Quantization/PaletteQuantizer{TPixel}.cs b/src/ImageSharp/Processing/Processors/Quantization/PaletteQuantizer{TPixel}.cs
index 712204bbfe..c29a361592 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/PaletteQuantizer{TPixel}.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/PaletteQuantizer{TPixel}.cs
@@ -98,6 +98,7 @@ public readonly IndexedImageFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> sourc
     [MethodImpl(InliningOptions.ShortMethod)]
     public readonly byte GetQuantizedColor(TPixel color, out TPixel match)
     {
+        // TODO: We need to use thesholding here.
         if (this.transparencyIndex >= 0 && color.Equals(this.transparentColor))
         {
             match = this.transparentColor;
diff --git a/src/ImageSharp/Processing/Processors/Quantization/QuantizerOptions.cs b/src/ImageSharp/Processing/Processors/Quantization/QuantizerOptions.cs
index 85db2b7c4e..9d32f737e5 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/QuantizerOptions.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/QuantizerOptions.cs
@@ -1,6 +1,7 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
+using SixLabors.ImageSharp.Formats;
 using SixLabors.ImageSharp.Processing.Processors.Dithering;
 
 namespace SixLabors.ImageSharp.Processing.Processors.Quantization;
@@ -8,7 +9,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization;
 /// <summary>
 /// Defines options for quantization.
 /// </summary>
-public class QuantizerOptions
+public class QuantizerOptions : IDeepCloneable<QuantizerOptions>
 {
 #pragma warning disable IDE0032 // Use auto property
     private float ditherScale = QuantizerConstants.MaxDitherScale;
@@ -16,6 +17,27 @@ public class QuantizerOptions
     private float threshold = QuantizerConstants.DefaultTransparencyThreshold;
 #pragma warning restore IDE0032 // Use auto property
 
+    /// <summary>
+    /// Initializes a new instance of the <see cref="QuantizerOptions"/> class.
+    /// </summary>
+    public QuantizerOptions()
+    {
+    }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="QuantizerOptions"/> class.
+    /// </summary>
+    /// <param name="options">The options to clone.</param>
+    private QuantizerOptions(QuantizerOptions options)
+    {
+        this.Dither = options.Dither;
+        this.DitherScale = options.DitherScale;
+        this.MaxColors = options.MaxColors;
+        this.TransparencyThreshold = options.TransparencyThreshold;
+        this.ColorMatchingMode = options.ColorMatchingMode;
+        this.TransparentColorMode = options.TransparentColorMode;
+    }
+
     /// <summary>
     /// Gets or sets the  algorithm to apply to the output image.
     /// Defaults to <see cref="QuantizerConstants.DefaultDither"/>; set to <see langword="null"/> for no dithering.
@@ -42,6 +64,12 @@ public int MaxColors
         set => this.maxColors = Numerics.Clamp(value, QuantizerConstants.MinColors, QuantizerConstants.MaxColors);
     }
 
+    /// <summary>
+    /// Gets or sets the color matching mode used for matching pixel values to palette colors.
+    /// Defaults to <see cref="ColorMatchingMode.Coarse"/>.
+    /// </summary>
+    public ColorMatchingMode ColorMatchingMode { get; set; } = ColorMatchingMode.Coarse;
+
     /// <summary>
     /// Gets or sets the threshold at which to consider a pixel transparent. Range 0..1.
     /// Defaults to <see cref="QuantizerConstants.DefaultTransparencyThreshold"/>.
@@ -53,14 +81,11 @@ public float TransparencyThreshold
     }
 
     /// <summary>
-    /// Gets or sets the color used for replacing colors with an alpha component below the threshold.
-    /// Defaults to <see cref="Color.Transparent"/>.
+    /// Gets or sets the transparent color mode used for handling transparent colors.
+    /// Defaults to <see cref="TransparentColorMode.Preserve"/>.
     /// </summary>
-    public Color ThresholdReplacementColor { get; set; } = Color.Transparent;
+    public TransparentColorMode TransparentColorMode { get; set; } = TransparentColorMode.Preserve;
 
-    /// <summary>
-    /// Gets or sets the color matching mode used for matching pixel values to palette colors.
-    /// Defaults to <see cref="ColorMatchingMode.Coarse"/>.
-    /// </summary>
-    public ColorMatchingMode ColorMatchingMode { get; set; } = ColorMatchingMode.Coarse;
+    /// <inheritdoc/>
+    public QuantizerOptions DeepClone() => new(this);
 }
diff --git a/src/ImageSharp/Processing/Processors/Quantization/QuantizerUtilities.cs b/src/ImageSharp/Processing/Processors/Quantization/QuantizerUtilities.cs
index d2d9d68b4f..bf9ae2af00 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/QuantizerUtilities.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/QuantizerUtilities.cs
@@ -18,6 +18,13 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization;
 /// </summary>
 public static class QuantizerUtilities
 {
+    internal static QuantizerOptions DeepClone(this QuantizerOptions options, Action<QuantizerOptions>? mutate)
+    {
+        QuantizerOptions clone = options.DeepClone();
+        mutate?.Invoke(clone);
+        return clone;
+    }
+
     /// <summary>
     /// Determines if transparent pixels can be replaced based on the specified color mode and pixel type.
     /// </summary>
@@ -29,20 +36,15 @@ public static bool ShouldReplacePixelsByAlphaThreshold<TPixel>(float threshold)
         => threshold > 0 && TPixel.GetPixelTypeInfo().AlphaRepresentation == PixelAlphaRepresentation.Unassociated;
 
     /// <summary>
-    /// Replaces transparent pixels in a span with a specified color based on an alpha threshold.
+    /// Replaces pixels in a span with fully transparent pixels based on an alpha threshold.
     /// </summary>
     /// <param name="source">A span of color vectors that will be checked for transparency and potentially modified.</param>
-    /// <param name="replacement">A color vector that will replace transparent pixels when the alpha value is below the specified threshold.</param>
     /// <param name="threshold">The alpha threshold used to determine if a pixel is transparent.</param>
-    public static void ReplacePixelsByAlphaThreshold(Span<Vector4> source, Vector4 replacement, float threshold)
+    public static void ReplacePixelsByAlphaThreshold(Span<Vector4> source, float threshold)
     {
         if (Vector512.IsHardwareAccelerated && source.Length >= 4)
         {
-            Vector128<float> replacement128 = replacement.AsVector128();
-            Vector256<float> replacement256 = Vector256.Create(replacement128, replacement128);
-            Vector512<float> replacement512 = Vector512.Create(replacement256, replacement256);
             Vector512<float> threshold512 = Vector512.Create(threshold);
-
             Span<Vector512<float>> source512 = MemoryMarshal.Cast<Vector4, Vector512<float>>(source);
             for (int i = 0; i < source512.Length; i++)
             {
@@ -56,7 +58,7 @@ public static void ReplacePixelsByAlphaThreshold(Span<Vector4> source, Vector4 r
 
                 // Use the mask to select the replacement vector
                 // (replacement & mask) | (v512 & ~mask)
-                v = Vector512.ConditionalSelect(mask, replacement512, v);
+                v = Vector512.ConditionalSelect(mask, Vector512<float>.Zero, v);
             }
 
             int m = Numerics.Modulo4(source.Length);
@@ -66,17 +68,14 @@ public static void ReplacePixelsByAlphaThreshold(Span<Vector4> source, Vector4 r
                 {
                     if (source[i].W < threshold)
                     {
-                        source[i] = replacement;
+                        source[i] = Vector4.Zero;
                     }
                 }
             }
         }
         else if (Vector256.IsHardwareAccelerated && source.Length >= 2)
         {
-            Vector128<float> replacement128 = replacement.AsVector128();
-            Vector256<float> replacement256 = Vector256.Create(replacement128, replacement128);
             Vector256<float> threshold256 = Vector256.Create(threshold);
-
             Span<Vector256<float>> source256 = MemoryMarshal.Cast<Vector4, Vector256<float>>(source);
             for (int i = 0; i < source256.Length; i++)
             {
@@ -90,7 +89,7 @@ public static void ReplacePixelsByAlphaThreshold(Span<Vector4> source, Vector4 r
 
                 // Use the mask to select the replacement vector
                 // (replacement & mask) | (v256 & ~mask)
-                v = Vector256.ConditionalSelect(mask, replacement256, v);
+                v = Vector256.ConditionalSelect(mask, Vector256<float>.Zero, v);
             }
 
             int m = Numerics.Modulo2(source.Length);
@@ -100,14 +99,13 @@ public static void ReplacePixelsByAlphaThreshold(Span<Vector4> source, Vector4 r
                 {
                     if (source[i].W < threshold)
                     {
-                        source[i] = replacement;
+                        source[i] = Vector4.Zero;
                     }
                 }
             }
         }
         else if (Vector128.IsHardwareAccelerated)
         {
-            Vector128<float> replacement128 = replacement.AsVector128();
             Vector128<float> threshold128 = Vector128.Create(threshold);
 
             for (int i = 0; i < source.Length; i++)
@@ -123,7 +121,7 @@ public static void ReplacePixelsByAlphaThreshold(Span<Vector4> source, Vector4 r
 
                 // Use the mask to select the replacement vector
                 // (replacement & mask) | (v128 & ~mask)
-                v = Vector128.ConditionalSelect(mask, replacement128, v128).AsVector4();
+                v = Vector128.ConditionalSelect(mask, Vector128<float>.Zero, v128).AsVector4();
             }
         }
         else
@@ -132,7 +130,7 @@ public static void ReplacePixelsByAlphaThreshold(Span<Vector4> source, Vector4 r
             {
                 if (source[i].W < threshold)
                 {
-                    source[i] = replacement;
+                    source[i] = Vector4.Zero;
                 }
             }
         }
@@ -336,7 +334,7 @@ internal static void AddPaletteColors<TFrameQuantizer, TPixel, TPixel2, TDelegat
     {
         Configuration configuration = quantizer.Configuration;
         float threshold = quantizer.Options.TransparencyThreshold;
-        Color replacement = quantizer.Options.ThresholdReplacementColor;
+        TransparentColorMode mode = quantizer.Options.TransparentColorMode;
 
         using IMemoryOwner<TPixel2> delegateRowOwner = configuration.MemoryAllocator.Allocate<TPixel2>(source.Width);
         Span<TPixel2> delegateRow = delegateRowOwner.Memory.Span;
@@ -348,7 +346,6 @@ internal static void AddPaletteColors<TFrameQuantizer, TPixel, TPixel2, TDelegat
         {
             using IMemoryOwner<Vector4> vectorRowOwner = configuration.MemoryAllocator.Allocate<Vector4>(source.Width);
             Span<Vector4> vectorRow = vectorRowOwner.Memory.Span;
-            Vector4 replacementV4 = replacement.ToScaledVector4();
 
             if (replaceByThreshold)
             {
@@ -357,7 +354,7 @@ internal static void AddPaletteColors<TFrameQuantizer, TPixel, TPixel2, TDelegat
                     Span<TPixel> sourceRow = source.DangerousGetRowSpan(y);
                     PixelOperations<TPixel>.Instance.ToVector4(configuration, sourceRow, vectorRow, PixelConversionModifiers.Scale);
 
-                    ReplacePixelsByAlphaThreshold(vectorRow, replacementV4, threshold);
+                    ReplacePixelsByAlphaThreshold(vectorRow, threshold);
 
                     PixelOperations<TPixel2>.Instance.FromVector4Destructive(configuration, vectorRow, delegateRow, PixelConversionModifiers.Scale);
                     rowDelegate.Invoke(delegateRow, y);
@@ -370,7 +367,7 @@ internal static void AddPaletteColors<TFrameQuantizer, TPixel, TPixel2, TDelegat
                     Span<TPixel> sourceRow = source.DangerousGetRowSpan(y);
                     PixelOperations<TPixel>.Instance.ToVector4(configuration, sourceRow, vectorRow, PixelConversionModifiers.Scale);
 
-                    EncodingUtilities.ReplaceTransparentPixels(vectorRow, replacementV4);
+                    EncodingUtilities.ReplaceTransparentPixels(vectorRow);
 
                     PixelOperations<TPixel2>.Instance.FromVector4Destructive(configuration, vectorRow, delegateRow, PixelConversionModifiers.Scale);
                     rowDelegate.Invoke(delegateRow, y);
@@ -398,10 +395,8 @@ private static void SecondPass<TFrameQuantizer, TPixel>(
         where TPixel : unmanaged, IPixel<TPixel>
     {
         float threshold = quantizer.Options.TransparencyThreshold;
-        Color replacement = quantizer.Options.ThresholdReplacementColor;
         bool replaceByThreshold = ShouldReplacePixelsByAlphaThreshold<TPixel>(threshold);
         bool replaceTransparent = EncodingUtilities.ShouldReplaceTransparentPixels<TPixel>(mode);
-        Vector4 replacementV4 = replacement.ToScaledVector4();
 
         IDither? dither = quantizer.Options.Dither;
         Buffer2D<TPixel> sourceBuffer = source.PixelBuffer;
@@ -426,7 +421,7 @@ private static void SecondPass<TFrameQuantizer, TPixel>(
                         Span<TPixel> sourceRow = region.DangerousGetRowSpan(y);
                         PixelOperations<TPixel>.Instance.ToVector4(configuration, sourceRow, vectorRow, PixelConversionModifiers.Scale);
 
-                        ReplacePixelsByAlphaThreshold(vectorRow, replacementV4, threshold);
+                        ReplacePixelsByAlphaThreshold(vectorRow, threshold);
 
                         PixelOperations<TPixel>.Instance.FromVector4Destructive(configuration, vectorRow, quantizingRow, PixelConversionModifiers.Scale);
 
@@ -444,7 +439,7 @@ private static void SecondPass<TFrameQuantizer, TPixel>(
                         Span<TPixel> sourceRow = region.DangerousGetRowSpan(y);
                         PixelOperations<TPixel>.Instance.ToVector4(configuration, sourceRow, vectorRow, PixelConversionModifiers.Scale);
 
-                        EncodingUtilities.ReplaceTransparentPixels(vectorRow, replacementV4);
+                        EncodingUtilities.ReplaceTransparentPixels(vectorRow);
 
                         PixelOperations<TPixel>.Instance.FromVector4Destructive(configuration, vectorRow, quantizingRow, PixelConversionModifiers.Scale);
 
@@ -483,7 +478,7 @@ private static void SecondPass<TFrameQuantizer, TPixel>(
                     Span<TPixel> sourceRow = region.DangerousGetRowSpan(y);
                     PixelOperations<TPixel>.Instance.ToVector4(configuration, sourceRow, vectorRow, PixelConversionModifiers.Scale);
 
-                    ReplacePixelsByAlphaThreshold(vectorRow, replacementV4, threshold);
+                    ReplacePixelsByAlphaThreshold(vectorRow, threshold);
 
                     PixelOperations<TPixel>.Instance.FromVector4Destructive(configuration, vectorRow, sourceRow, PixelConversionModifiers.Scale);
                 }
@@ -495,7 +490,7 @@ private static void SecondPass<TFrameQuantizer, TPixel>(
                     Span<TPixel> sourceRow = region.DangerousGetRowSpan(y);
                     PixelOperations<TPixel>.Instance.ToVector4(configuration, sourceRow, vectorRow, PixelConversionModifiers.Scale);
 
-                    EncodingUtilities.ReplaceTransparentPixels(vectorRow, replacementV4);
+                    EncodingUtilities.ReplaceTransparentPixels(vectorRow);
 
                     PixelOperations<TPixel>.Instance.FromVector4Destructive(configuration, vectorRow, sourceRow, PixelConversionModifiers.Scale);
                 }
diff --git a/src/ImageSharp/Processing/Processors/Quantization/WuQuantizer{TPixel}.cs b/src/ImageSharp/Processing/Processors/Quantization/WuQuantizer{TPixel}.cs
index a132aa2813..4b709838ef 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/WuQuantizer{TPixel}.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/WuQuantizer{TPixel}.cs
@@ -58,9 +58,6 @@ internal struct WuQuantizer<TPixel> : IQuantizer<TPixel>
     private readonly Box[] colorCube;
     private PixelMap<TPixel>? pixelMap;
     private readonly bool isDithering;
-    private readonly int transparencyThreshold255;
-    private Vector4 thresholdReplacementColorV4;
-    private readonly Rgba32 thresholdReplacementColorRgba;
     private bool isDisposed;
 
     /// <summary>
@@ -86,9 +83,6 @@ public WuQuantizer(Configuration configuration, QuantizerOptions options)
         this.pixelMap = default;
         this.palette = default;
         this.isDithering = this.Options.Dither is not null;
-        this.transparencyThreshold255 = (int)(this.Options.TransparencyThreshold * 255F);
-        this.thresholdReplacementColorV4 = this.Options.ThresholdReplacementColor.ToScaledVector4();
-        this.thresholdReplacementColorRgba = this.Options.ThresholdReplacementColor.ToPixel<Rgba32>();
     }
 
     /// <inheritdoc/>
@@ -139,7 +133,6 @@ private void ResolvePalette()
         ReadOnlySpan<Moment> momentsSpan = this.momentsOwner.GetSpan();
 
         float transparencyThreshold = this.Options.TransparencyThreshold;
-        Vector4 thresholdReplacementColor = this.thresholdReplacementColorV4;
         for (int k = 0; k < paletteSpan.Length; k++)
         {
             this.Mark(ref this.colorCube[k], (byte)k);
@@ -149,7 +142,7 @@ private void ResolvePalette()
                 Vector4 normalized = moment.Normalize();
                 if (normalized.W < transparencyThreshold)
                 {
-                    normalized = thresholdReplacementColor;
+                    normalized = Vector4.Zero;
                 }
 
                 paletteSpan[k] = TPixel.FromScaledVector4(normalized);
@@ -188,10 +181,6 @@ public readonly byte GetQuantizedColor(TPixel color, out TPixel match)
         }
 
         Rgba32 rgba = color.ToRgba32();
-        if (rgba.A < this.transparencyThreshold255)
-        {
-            rgba = this.thresholdReplacementColorRgba;
-        }
 
         const int shift = 8 - IndexBits;
         int r = rgba.R >> shift;

From 2c6aceaeacf63a98a27588615e83d19b4e4db788 Mon Sep 17 00:00:00 2001
From: James Jackson-South <james_south@hotmail.com>
Date: Thu, 27 Mar 2025 23:19:16 +1000
Subject: [PATCH 12/18] Set langversion to 12

---
 Directory.Build.props | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Directory.Build.props b/Directory.Build.props
index 1191e848ef..755cbe3b30 100644
--- a/Directory.Build.props
+++ b/Directory.Build.props
@@ -22,7 +22,7 @@
   <Import Project="$(MSBuildThisFileDirectory)shared-infrastructure\msbuild\props\SixLabors.Global.props" />
 
   <PropertyGroup>
-    <LangVersion>13.0</LangVersion>
+    <LangVersion>12.0</LangVersion>
   </PropertyGroup>
 
   <!--

From 16b4eb6c814fe033b46d3674c8a6eca8e83a3c59 Mon Sep 17 00:00:00 2001
From: James Jackson-South <james_south@hotmail.com>
Date: Fri, 28 Mar 2025 21:14:03 +1000
Subject: [PATCH 13/18] Simplify API and clone options.

---
 .../Formats/AlphaAwareImageEncoder.cs         |  4 +
 src/ImageSharp/Formats/Gif/GifEncoderCore.cs  | 39 +++++---
 src/ImageSharp/Formats/Png/PngEncoderCore.cs  | 13 ++-
 .../Formats/TransparentColorMode.cs           |  2 +-
 .../Quantization/IQuantizer{TPixel}.cs        | 29 +-----
 .../IQuantizingPixelRowDelegate{TPixel}.cs    |  6 --
 .../Quantization/OctreeQuantizer{TPixel}.cs   | 20 +----
 .../Quantization/PaletteQuantizer{TPixel}.cs  | 14 +--
 .../Quantization/QuantizerOptions.cs          |  3 +-
 .../Quantization/QuantizerUtilities.cs        | 90 ++++---------------
 .../Quantization/WuQuantizer{TPixel}.cs       | 20 +----
 11 files changed, 72 insertions(+), 168 deletions(-)

diff --git a/src/ImageSharp/Formats/AlphaAwareImageEncoder.cs b/src/ImageSharp/Formats/AlphaAwareImageEncoder.cs
index f753e7282b..1c1a8b2910 100644
--- a/src/ImageSharp/Formats/AlphaAwareImageEncoder.cs
+++ b/src/ImageSharp/Formats/AlphaAwareImageEncoder.cs
@@ -1,6 +1,8 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
+using SixLabors.ImageSharp.Processing.Processors.Quantization;
+
 namespace SixLabors.ImageSharp.Formats;
 
 /// <summary>
@@ -10,6 +12,8 @@ public abstract class AlphaAwareImageEncoder : ImageEncoder
 {
     /// <summary>
     /// Gets or initializes the mode that determines how transparent pixels are handled during encoding.
+    /// This overrides any other settings that may affect the encoding of transparent pixels
+    /// including those passed via <see cref="QuantizerOptions"/>.
     /// </summary>
     public TransparentColorMode TransparentColorMode { get; init; }
 }
diff --git a/src/ImageSharp/Formats/Gif/GifEncoderCore.cs b/src/ImageSharp/Formats/Gif/GifEncoderCore.cs
index 114cb4347f..c0d74e03e6 100644
--- a/src/ImageSharp/Formats/Gif/GifEncoderCore.cs
+++ b/src/ImageSharp/Formats/Gif/GifEncoderCore.cs
@@ -150,10 +150,7 @@ public void Encode<TPixel>(Image<TPixel> image, Stream stream, CancellationToken
         TransparentColorMode mode = this.transparentColorMode;
         QuantizerOptions options = this.quantizer.Options.DeepClone(o => o.TransparentColorMode = mode);
 
-        // Quantize the first frame. Checking to see whether we can clear the transparent pixels
-        // to allow for a smaller color palette and encoded result.
-        // TODO: What should we use as the background color here?
-        Color background = Color.Transparent;
+        // Quantize the first frame.
         using (IQuantizer<TPixel> frameQuantizer = this.quantizer.CreatePixelSpecificQuantizer<TPixel>(this.configuration, options))
         {
             IPixelSamplingStrategy strategy = this.pixelSamplingStrategy;
@@ -163,12 +160,12 @@ public void Encode<TPixel>(Image<TPixel> image, Stream stream, CancellationToken
             {
                 if (useGlobalTable)
                 {
-                    frameQuantizer.BuildPalette(mode, strategy, image);
+                    frameQuantizer.BuildPalette(strategy, image);
                     quantized = frameQuantizer.QuantizeFrame(encodingFrame, image.Bounds);
                 }
                 else
                 {
-                    frameQuantizer.BuildPalette(mode, strategy, encodingFrame);
+                    frameQuantizer.BuildPalette(strategy, encodingFrame);
                     quantized = frameQuantizer.QuantizeFrame(encodingFrame, encodingFrame.Bounds);
                 }
             }
@@ -176,13 +173,14 @@ public void Encode<TPixel>(Image<TPixel> image, Stream stream, CancellationToken
             {
                 quantized = this.QuantizeAdditionalFrameAndUpdateMetadata(
                     encodingFrame,
+                    options,
                     encodingFrame.Bounds,
                     frameMetadata,
                     true,
                     default,
                     false,
                     frameMetadata.HasTransparency ? frameMetadata.TransparencyIndex : -1,
-                    background);
+                    Color.Transparent);
             }
         }
 
@@ -197,6 +195,7 @@ public void Encode<TPixel>(Image<TPixel> image, Stream stream, CancellationToken
             frameMetadata.TransparencyIndex = ClampIndex(derivedTransparencyIndex);
         }
 
+        // TODO: We should be checking the metadata here also I think?
         if (!TryGetBackgroundIndex(quantized, this.backgroundColor, out byte backgroundIndex))
         {
             backgroundIndex = derivedTransparencyIndex >= 0
@@ -235,6 +234,7 @@ public void Encode<TPixel>(Image<TPixel> image, Stream stream, CancellationToken
             this.EncodeAdditionalFrames(
                 stream,
                 image,
+                options,
                 globalPalette,
                 derivedTransparencyIndex,
                 frameMetadata.DisposalMode,
@@ -264,6 +264,7 @@ private static GifFrameMetadata GetGifFrameMetadata<TPixel>(ImageFrame<TPixel> f
     private void EncodeAdditionalFrames<TPixel>(
         Stream stream,
         Image<TPixel> image,
+        QuantizerOptions options,
         ReadOnlyMemory<TPixel> globalPalette,
         int globalTransparencyIndex,
         FrameDisposalMode previousDisposalMode,
@@ -301,7 +302,7 @@ private void EncodeAdditionalFrames<TPixel>(
                     // The palette quantizer can reuse the same global pixel map across multiple frames since the palette is unchanging.
                     // This allows a reduction of memory usage across multi-frame gifs using a global palette
                     // and also allows use to reuse the cache from previous runs.
-                    globalPaletteQuantizer = new(this.configuration, this.quantizer!.Options, globalPalette);
+                    globalPaletteQuantizer = new(this.configuration, options, globalPalette);
                     hasGlobalPaletteQuantizer = true;
                 }
 
@@ -311,6 +312,7 @@ private void EncodeAdditionalFrames<TPixel>(
                     currentFrame,
                     nextFrame,
                     encodingFrame,
+                    options,
                     useLocal,
                     gifMetadata,
                     globalPaletteQuantizer,
@@ -361,6 +363,7 @@ private void EncodeAdditionalFrame<TPixel>(
         ImageFrame<TPixel> currentFrame,
         ImageFrame<TPixel>? nextFrame,
         ImageFrame<TPixel> encodingFrame,
+        QuantizerOptions options,
         bool useLocal,
         GifFrameMetadata metadata,
         PaletteQuantizer<TPixel> globalPaletteQuantizer,
@@ -392,6 +395,7 @@ private void EncodeAdditionalFrame<TPixel>(
 
         using IndexedImageFrame<TPixel> quantized = this.QuantizeAdditionalFrameAndUpdateMetadata(
                 encodingFrame,
+                options,
                 bounds,
                 metadata,
                 useLocal,
@@ -416,6 +420,7 @@ private void EncodeAdditionalFrame<TPixel>(
 
     private IndexedImageFrame<TPixel> QuantizeAdditionalFrameAndUpdateMetadata<TPixel>(
         ImageFrame<TPixel> encodingFrame,
+        QuantizerOptions options,
         Rectangle bounds,
         GifFrameMetadata metadata,
         bool useLocal,
@@ -446,7 +451,12 @@ private IndexedImageFrame<TPixel> QuantizeAdditionalFrameAndUpdateMetadata<TPixe
                         transparencyIndex = palette.Length;
                         metadata.TransparencyIndex = ClampIndex(transparencyIndex);
 
-                        PaletteQuantizer quantizer = new(palette, new() { Dither = null }, transparencyIndex, transparentColor);
+                        QuantizerOptions paletteOptions = options.DeepClone(o =>
+                        {
+                            o.MaxColors = palette.Length;
+                            o.Dither = null;
+                        });
+                        PaletteQuantizer quantizer = new(palette, paletteOptions, transparencyIndex, transparentColor);
                         using IQuantizer<TPixel> frameQuantizer = quantizer.CreatePixelSpecificQuantizer<TPixel>(this.configuration, quantizer.Options);
                         quantized = frameQuantizer.BuildPaletteAndQuantizeFrame(encodingFrame, bounds);
                     }
@@ -454,7 +464,7 @@ private IndexedImageFrame<TPixel> QuantizeAdditionalFrameAndUpdateMetadata<TPixe
                     {
                         // We must quantize the frame to generate a local color table.
                         IQuantizer quantizer = this.hasQuantizer ? this.quantizer! : FallbackQuantizer;
-                        using IQuantizer<TPixel> frameQuantizer = quantizer.CreatePixelSpecificQuantizer<TPixel>(this.configuration, quantizer.Options);
+                        using IQuantizer<TPixel> frameQuantizer = quantizer.CreatePixelSpecificQuantizer<TPixel>(this.configuration, options);
                         quantized = frameQuantizer.BuildPaletteAndQuantizeFrame(encodingFrame, bounds);
 
                         // The transparency index derived by the quantizer will differ from the index
@@ -466,7 +476,12 @@ private IndexedImageFrame<TPixel> QuantizeAdditionalFrameAndUpdateMetadata<TPixe
                 else
                 {
                     // Just use the local palette.
-                    PaletteQuantizer quantizer = new(palette, new() { Dither = null }, transparencyIndex, transparentColor);
+                    QuantizerOptions paletteOptions = options.DeepClone(o =>
+                    {
+                        o.MaxColors = palette.Length;
+                        o.Dither = null;
+                    });
+                    PaletteQuantizer quantizer = new(palette, paletteOptions, transparencyIndex, transparentColor);
                     using IQuantizer<TPixel> frameQuantizer = quantizer.CreatePixelSpecificQuantizer<TPixel>(this.configuration, quantizer.Options);
                     quantized = frameQuantizer.BuildPaletteAndQuantizeFrame(encodingFrame, bounds);
                 }
@@ -475,7 +490,7 @@ private IndexedImageFrame<TPixel> QuantizeAdditionalFrameAndUpdateMetadata<TPixe
             {
                 // We must quantize the frame to generate a local color table.
                 IQuantizer quantizer = this.hasQuantizer ? this.quantizer! : FallbackQuantizer;
-                using IQuantizer<TPixel> frameQuantizer = quantizer.CreatePixelSpecificQuantizer<TPixel>(this.configuration, quantizer.Options);
+                using IQuantizer<TPixel> frameQuantizer = quantizer.CreatePixelSpecificQuantizer<TPixel>(this.configuration, options);
                 quantized = frameQuantizer.BuildPaletteAndQuantizeFrame(encodingFrame, bounds);
 
                 // The transparency index derived by the quantizer might differ from the index
diff --git a/src/ImageSharp/Formats/Png/PngEncoderCore.cs b/src/ImageSharp/Formats/Png/PngEncoderCore.cs
index 07be36ae27..e9b76522c9 100644
--- a/src/ImageSharp/Formats/Png/PngEncoderCore.cs
+++ b/src/ImageSharp/Formats/Png/PngEncoderCore.cs
@@ -1574,13 +1574,21 @@ private void SanitizeAndSetEncoderOptions<TPixel>(
             {
                 // We can use the color data from the decoded metadata here.
                 // We avoid dithering by default to preserve the original colors.
-                this.quantizer = new PaletteQuantizer(metadata.ColorTable.Value, new() { Dither = null });
+                QuantizerOptions options = new() { Dither = null, TransparentColorMode = encoder.TransparentColorMode };
+                this.quantizer = new PaletteQuantizer(metadata.ColorTable.Value, options);
             }
             else
             {
                 // Don't use the default transparency threshold for quantization as PNG can handle multiple transparent colors.
                 // We choose a value that is close to zero so that edge cases causes by lower bit depths for the alpha channel are handled correctly.
-                this.quantizer = new WuQuantizer(new QuantizerOptions { TransparencyThreshold = 0, MaxColors = ColorNumerics.GetColorCountForBitDepth(bitDepth) });
+                QuantizerOptions options = new()
+                {
+                    TransparencyThreshold = 0,
+                    MaxColors = ColorNumerics.GetColorCountForBitDepth(bitDepth),
+                    TransparentColorMode = encoder.TransparentColorMode
+                };
+
+                this.quantizer = new WuQuantizer(options);
             }
         }
 
@@ -1604,7 +1612,6 @@ private void SanitizeAndSetEncoderOptions<TPixel>(
         }
 
         frameQuantizer.BuildPalette(
-            encoder.TransparentColorMode,
             encoder.PixelSamplingStrategy,
             image);
 
diff --git a/src/ImageSharp/Formats/TransparentColorMode.cs b/src/ImageSharp/Formats/TransparentColorMode.cs
index c4d9c927e6..fe88c314f2 100644
--- a/src/ImageSharp/Formats/TransparentColorMode.cs
+++ b/src/ImageSharp/Formats/TransparentColorMode.cs
@@ -4,7 +4,7 @@
 namespace SixLabors.ImageSharp.Formats;
 
 /// <summary>
-/// Specifies how transparent pixels should be handled during encoding and quantization.
+/// Specifies how pixels with transparent alpha components should be handled during encoding and quantization.
 /// </summary>
 public enum TransparentColorMode
 {
diff --git a/src/ImageSharp/Processing/Processors/Quantization/IQuantizer{TPixel}.cs b/src/ImageSharp/Processing/Processors/Quantization/IQuantizer{TPixel}.cs
index 02c2052fef..1e6420eaa9 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/IQuantizer{TPixel}.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/IQuantizer{TPixel}.cs
@@ -1,7 +1,6 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
-using SixLabors.ImageSharp.Formats;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;
 
@@ -36,37 +35,13 @@ public interface IQuantizer<TPixel> : IDisposable
     /// Adds colors to the quantized palette from the given pixel source.
     /// </summary>
     /// <param name="pixelRegion">The <see cref="Buffer2DRegion{T}"/> of source pixels to register.</param>
-    public void AddPaletteColors(in Buffer2DRegion<TPixel> pixelRegion)
-        => this.AddPaletteColors(pixelRegion, TransparentColorMode.Preserve);
-
-    /// <summary>
-    /// Adds colors to the quantized palette from the given pixel source.
-    /// </summary>
-    /// <param name="pixelRegion">The <see cref="Buffer2DRegion{T}"/> of source pixels to register.</param>
-    /// <param name="mode">The <see cref="TransparentColorMode"/> to use when adding colors to the palette.</param>
-    public void AddPaletteColors(in Buffer2DRegion<TPixel> pixelRegion, TransparentColorMode mode);
-
-    /// <summary>
-    /// Quantizes an image frame and return the resulting output pixels.
-    /// </summary>
-    /// <param name="source">The source image frame to quantize.</param>
-    /// <param name="bounds">The bounds within the frame to quantize.</param>
-    /// <returns>
-    /// A <see cref="IndexedImageFrame{TPixel}"/> representing a quantized version of the source frame pixels.
-    /// </returns>
-    /// <remarks>
-    /// Only executes the second (quantization) step. The palette has to be built by calling <see cref="AddPaletteColors(in Buffer2DRegion{TPixel})"/>.
-    /// To run both steps, use <see cref="QuantizerUtilities.BuildPaletteAndQuantizeFrame{TPixel}(IQuantizer{TPixel}, ImageFrame{TPixel}, Rectangle)"/>.
-    /// </remarks>
-    public IndexedImageFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> source, Rectangle bounds)
-        => this.QuantizeFrame(source, bounds, TransparentColorMode.Preserve);
+    public void AddPaletteColors(in Buffer2DRegion<TPixel> pixelRegion);
 
     /// <summary>
     /// Quantizes an image frame and return the resulting output pixels.
     /// </summary>
     /// <param name="source">The source image frame to quantize.</param>
     /// <param name="bounds">The bounds within the frame to quantize.</param>
-    /// <param name="mode">The <see cref="TransparentColorMode"/> to use when quantizing the frame.</param>
     /// <returns>
     /// A <see cref="IndexedImageFrame{TPixel}"/> representing a quantized version of the source frame pixels.
     /// </returns>
@@ -74,7 +49,7 @@ public IndexedImageFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> source, Rectan
     /// Only executes the second (quantization) step. The palette has to be built by calling <see cref="AddPaletteColors(in Buffer2DRegion{TPixel})"/>.
     /// To run both steps, use <see cref="QuantizerUtilities.BuildPaletteAndQuantizeFrame{TPixel}(IQuantizer{TPixel}, ImageFrame{TPixel}, Rectangle)"/>.
     /// </remarks>
-    public IndexedImageFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> source, Rectangle bounds, TransparentColorMode mode);
+    public IndexedImageFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> source, Rectangle bounds);
 
     /// <summary>
     /// Returns the index and color from the quantized palette corresponding to the given color.
diff --git a/src/ImageSharp/Processing/Processors/Quantization/IQuantizingPixelRowDelegate{TPixel}.cs b/src/ImageSharp/Processing/Processors/Quantization/IQuantizingPixelRowDelegate{TPixel}.cs
index ce06adf455..3cf4c93d62 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/IQuantizingPixelRowDelegate{TPixel}.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/IQuantizingPixelRowDelegate{TPixel}.cs
@@ -1,7 +1,6 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
-using SixLabors.ImageSharp.Formats;
 using SixLabors.ImageSharp.PixelFormats;
 
 namespace SixLabors.ImageSharp.Processing.Processors.Quantization;
@@ -13,11 +12,6 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization;
 internal interface IQuantizingPixelRowDelegate<TPixel>
     where TPixel : unmanaged, IPixel<TPixel>
 {
-    /// <summary>
-    /// Gets the transparent color mode to use when adding colors to the palette.
-    /// </summary>
-    public TransparentColorMode TransparentColorMode { get; }
-
     /// <summary>
     /// Processes a row of pixels for quantization.
     /// </summary>
diff --git a/src/ImageSharp/Processing/Processors/Quantization/OctreeQuantizer{TPixel}.cs b/src/ImageSharp/Processing/Processors/Quantization/OctreeQuantizer{TPixel}.cs
index 5f55a4410f..07596b68a8 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/OctreeQuantizer{TPixel}.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/OctreeQuantizer{TPixel}.cs
@@ -6,7 +6,6 @@
 using System.Numerics;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
-using SixLabors.ImageSharp.Formats;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;
 
@@ -75,9 +74,9 @@ public ReadOnlyMemory<TPixel> Palette
     }
 
     /// <inheritdoc/>
-    public readonly void AddPaletteColors(in Buffer2DRegion<TPixel> pixelRegion, TransparentColorMode mode)
+    public readonly void AddPaletteColors(in Buffer2DRegion<TPixel> pixelRegion)
     {
-        PixelRowDelegate pixelRowDelegate = new(this.octree, mode);
+        PixelRowDelegate pixelRowDelegate = new(this.octree);
         QuantizerUtilities.AddPaletteColors<OctreeQuantizer<TPixel>, TPixel, Rgba32, PixelRowDelegate>(
             ref Unsafe.AsRef(in this),
             in pixelRegion,
@@ -103,12 +102,7 @@ private void ResolvePalette()
     /// <inheritdoc/>
     [MethodImpl(InliningOptions.ShortMethod)]
     public readonly IndexedImageFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> source, Rectangle bounds)
-        => this.QuantizeFrame(source, bounds, TransparentColorMode.Preserve);
-
-    /// <inheritdoc/>
-    [MethodImpl(InliningOptions.ShortMethod)]
-    public readonly IndexedImageFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> source, Rectangle bounds, TransparentColorMode mode)
-        => QuantizerUtilities.QuantizeFrame(ref Unsafe.AsRef(in this), source, bounds, mode);
+        => QuantizerUtilities.QuantizeFrame(ref Unsafe.AsRef(in this), source, bounds);
 
     /// <inheritdoc/>
     [MethodImpl(InliningOptions.ShortMethod)]
@@ -146,13 +140,7 @@ public void Dispose()
     {
         private readonly Octree octree;
 
-        public PixelRowDelegate(Octree octree, TransparentColorMode mode)
-        {
-            this.octree = octree;
-            this.TransparentColorMode = mode;
-        }
-
-        public TransparentColorMode TransparentColorMode { get; }
+        public PixelRowDelegate(Octree octree) => this.octree = octree;
 
         public void Invoke(ReadOnlySpan<Rgba32> row, int rowIndex) => this.octree.AddColors(row);
     }
diff --git a/src/ImageSharp/Processing/Processors/Quantization/PaletteQuantizer{TPixel}.cs b/src/ImageSharp/Processing/Processors/Quantization/PaletteQuantizer{TPixel}.cs
index c29a361592..4fd044ab40 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/PaletteQuantizer{TPixel}.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/PaletteQuantizer{TPixel}.cs
@@ -3,7 +3,6 @@
 
 using System.Diagnostics.CodeAnalysis;
 using System.Runtime.CompilerServices;
-using SixLabors.ImageSharp.Formats;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;
 
@@ -76,29 +75,18 @@ public PaletteQuantizer(
     /// <inheritdoc/>
     [MethodImpl(InliningOptions.ShortMethod)]
     public readonly void AddPaletteColors(in Buffer2DRegion<TPixel> pixelRegion)
-        => this.AddPaletteColors(in pixelRegion, TransparentColorMode.Preserve);
-
-    /// <inheritdoc/>
-    [MethodImpl(InliningOptions.ShortMethod)]
-    public readonly void AddPaletteColors(in Buffer2DRegion<TPixel> pixelRegion, TransparentColorMode mode)
     {
     }
 
     /// <inheritdoc/>
     [MethodImpl(InliningOptions.ShortMethod)]
     public readonly IndexedImageFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> source, Rectangle bounds)
-        => this.QuantizeFrame(source, bounds, TransparentColorMode.Preserve);
-
-    /// <inheritdoc/>
-    [MethodImpl(InliningOptions.ShortMethod)]
-    public readonly IndexedImageFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> source, Rectangle bounds, TransparentColorMode mode)
-        => QuantizerUtilities.QuantizeFrame(ref Unsafe.AsRef(in this), source, bounds, mode);
+        => QuantizerUtilities.QuantizeFrame(ref Unsafe.AsRef(in this), source, bounds);
 
     /// <inheritdoc/>
     [MethodImpl(InliningOptions.ShortMethod)]
     public readonly byte GetQuantizedColor(TPixel color, out TPixel match)
     {
-        // TODO: We need to use thesholding here.
         if (this.transparencyIndex >= 0 && color.Equals(this.transparentColor))
         {
             match = this.transparentColor;
diff --git a/src/ImageSharp/Processing/Processors/Quantization/QuantizerOptions.cs b/src/ImageSharp/Processing/Processors/Quantization/QuantizerOptions.cs
index 9d32f737e5..16dfd5b330 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/QuantizerOptions.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/QuantizerOptions.cs
@@ -81,7 +81,8 @@ public float TransparencyThreshold
     }
 
     /// <summary>
-    /// Gets or sets the transparent color mode used for handling transparent colors.
+    /// Gets or sets the transparent color mode used for handling transparent colors
+    /// when not using thresholding.
     /// Defaults to <see cref="TransparentColorMode.Preserve"/>.
     /// </summary>
     public TransparentColorMode TransparentColorMode { get; set; } = TransparentColorMode.Preserve;
diff --git a/src/ImageSharp/Processing/Processors/Quantization/QuantizerUtilities.cs b/src/ImageSharp/Processing/Processors/Quantization/QuantizerUtilities.cs
index bf9ae2af00..e121aff90b 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/QuantizerUtilities.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/QuantizerUtilities.cs
@@ -18,7 +18,13 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization;
 /// </summary>
 public static class QuantizerUtilities
 {
-    internal static QuantizerOptions DeepClone(this QuantizerOptions options, Action<QuantizerOptions>? mutate)
+    /// <summary>
+    /// Performs a deep clone the <see cref="QuantizerOptions"/> instance and optionally mutates the clone.
+    /// </summary>
+    /// <param name="options">The <see cref="QuantizerOptions"/> instance to clone.</param>
+    /// <param name="mutate">An optional delegate to mutate the cloned instance.</param>
+    /// <returns>The cloned <see cref="QuantizerOptions"/> instance.</returns>
+    public static QuantizerOptions DeepClone(this QuantizerOptions options, Action<QuantizerOptions>? mutate)
     {
         QuantizerOptions clone = options.DeepClone();
         mutate?.Invoke(clone);
@@ -170,29 +176,6 @@ public static IndexedImageFrame<TPixel> BuildPaletteAndQuantizeFrame<TPixel>(
         ImageFrame<TPixel> source,
         Rectangle bounds)
         where TPixel : unmanaged, IPixel<TPixel>
-        => BuildPaletteAndQuantizeFrame(
-            quantizer,
-            source,
-            bounds,
-            TransparentColorMode.Preserve);
-
-    /// <summary>
-    /// Execute both steps of the quantization.
-    /// </summary>
-    /// <param name="quantizer">The pixel specific quantizer.</param>
-    /// <param name="source">The source image frame to quantize.</param>
-    /// <param name="bounds">The bounds within the frame to quantize.</param>
-    /// <param name="mode">The transparent color mode.</param>
-    /// <typeparam name="TPixel">The pixel type.</typeparam>
-    /// <returns>
-    /// A <see cref="IndexedImageFrame{TPixel}"/> representing a quantized version of the source frame pixels.
-    /// </returns>
-    public static IndexedImageFrame<TPixel> BuildPaletteAndQuantizeFrame<TPixel>(
-        this IQuantizer<TPixel> quantizer,
-        ImageFrame<TPixel> source,
-        Rectangle bounds,
-        TransparentColorMode mode)
-        where TPixel : unmanaged, IPixel<TPixel>
     {
         Guard.NotNull(quantizer, nameof(quantizer));
         Guard.NotNull(source, nameof(source));
@@ -200,7 +183,7 @@ public static IndexedImageFrame<TPixel> BuildPaletteAndQuantizeFrame<TPixel>(
         Rectangle interest = Rectangle.Intersect(source.Bounds, bounds);
         Buffer2DRegion<TPixel> region = source.PixelBuffer.GetRegion(interest);
 
-        quantizer.AddPaletteColors(in region, mode);
+        quantizer.AddPaletteColors(in region);
         return quantizer.QuantizeFrame(source, bounds);
     }
 
@@ -212,15 +195,13 @@ public static IndexedImageFrame<TPixel> BuildPaletteAndQuantizeFrame<TPixel>(
     /// <param name="quantizer">The pixel specific quantizer.</param>
     /// <param name="source">The source image frame to quantize.</param>
     /// <param name="bounds">The bounds within the frame to quantize.</param>
-    /// <param name="mode">The transparent color mode.</param>
     /// <returns>
     /// A <see cref="IndexedImageFrame{TPixel}"/> representing a quantized version of the source frame pixels.
     /// </returns>
     public static IndexedImageFrame<TPixel> QuantizeFrame<TFrameQuantizer, TPixel>(
         ref TFrameQuantizer quantizer,
         ImageFrame<TPixel> source,
-        Rectangle bounds,
-        TransparentColorMode mode)
+        Rectangle bounds)
         where TFrameQuantizer : struct, IQuantizer<TPixel>
         where TPixel : unmanaged, IPixel<TPixel>
     {
@@ -235,13 +216,13 @@ public static IndexedImageFrame<TPixel> QuantizeFrame<TFrameQuantizer, TPixel>(
 
         if (quantizer.Options.Dither is null)
         {
-            SecondPass(ref quantizer, source, destination, interest, mode);
+            SecondPass(ref quantizer, source, destination, interest);
         }
         else
         {
             // We clone the image as we don't want to alter the original via error diffusion based dithering.
             using ImageFrame<TPixel> clone = source.Clone();
-            SecondPass(ref quantizer, clone, destination, interest, mode);
+            SecondPass(ref quantizer, clone, destination, interest);
         }
 
         return destination;
@@ -259,29 +240,10 @@ public static void BuildPalette<TPixel>(
         IPixelSamplingStrategy pixelSamplingStrategy,
         Image<TPixel> source)
         where TPixel : unmanaged, IPixel<TPixel>
-        => quantizer.BuildPalette(
-            TransparentColorMode.Preserve,
-            pixelSamplingStrategy,
-            source);
-
-    /// <summary>
-    /// Adds colors to the quantized palette from the given pixel regions.
-    /// </summary>
-    /// <typeparam name="TPixel">The pixel format.</typeparam>
-    /// <param name="quantizer">The pixel specific quantizer.</param>
-    /// <param name="mode">The transparent color mode.</param>
-    /// <param name="pixelSamplingStrategy">The pixel sampling strategy.</param>
-    /// <param name="source">The source image to sample from.</param>
-    public static void BuildPalette<TPixel>(
-        this IQuantizer<TPixel> quantizer,
-        TransparentColorMode mode,
-        IPixelSamplingStrategy pixelSamplingStrategy,
-        Image<TPixel> source)
-        where TPixel : unmanaged, IPixel<TPixel>
     {
         foreach (Buffer2DRegion<TPixel> region in pixelSamplingStrategy.EnumeratePixelRegions(source))
         {
-            quantizer.AddPaletteColors(in region, mode);
+            quantizer.AddPaletteColors(in region);
         }
     }
 
@@ -297,29 +259,10 @@ public static void BuildPalette<TPixel>(
         IPixelSamplingStrategy pixelSamplingStrategy,
         ImageFrame<TPixel> source)
         where TPixel : unmanaged, IPixel<TPixel>
-        => quantizer.BuildPalette(
-            TransparentColorMode.Preserve,
-            pixelSamplingStrategy,
-            source);
-
-    /// <summary>
-    /// Adds colors to the quantized palette from the given pixel regions.
-    /// </summary>
-    /// <typeparam name="TPixel">The pixel format.</typeparam>
-    /// <param name="quantizer">The pixel specific quantizer.</param>
-    /// <param name="mode">The transparent color mode.</param>
-    /// <param name="pixelSamplingStrategy">The pixel sampling strategy.</param>
-    /// <param name="source">The source image frame to sample from.</param>
-    public static void BuildPalette<TPixel>(
-        this IQuantizer<TPixel> quantizer,
-        TransparentColorMode mode,
-        IPixelSamplingStrategy pixelSamplingStrategy,
-        ImageFrame<TPixel> source)
-        where TPixel : unmanaged, IPixel<TPixel>
     {
         foreach (Buffer2DRegion<TPixel> region in pixelSamplingStrategy.EnumeratePixelRegions(source))
         {
-            quantizer.AddPaletteColors(in region, mode);
+            quantizer.AddPaletteColors(in region);
         }
     }
 
@@ -340,7 +283,7 @@ internal static void AddPaletteColors<TFrameQuantizer, TPixel, TPixel2, TDelegat
         Span<TPixel2> delegateRow = delegateRowOwner.Memory.Span;
 
         bool replaceByThreshold = ShouldReplacePixelsByAlphaThreshold<TPixel>(threshold);
-        bool replaceTransparent = EncodingUtilities.ShouldReplaceTransparentPixels<TPixel>(rowDelegate.TransparentColorMode);
+        bool replaceTransparent = EncodingUtilities.ShouldReplaceTransparentPixels<TPixel>(mode);
 
         if (replaceByThreshold || replaceTransparent)
         {
@@ -389,13 +332,14 @@ private static void SecondPass<TFrameQuantizer, TPixel>(
         ref TFrameQuantizer quantizer,
         ImageFrame<TPixel> source,
         IndexedImageFrame<TPixel> destination,
-        Rectangle bounds,
-        TransparentColorMode mode)
+        Rectangle bounds)
         where TFrameQuantizer : struct, IQuantizer<TPixel>
         where TPixel : unmanaged, IPixel<TPixel>
     {
         float threshold = quantizer.Options.TransparencyThreshold;
         bool replaceByThreshold = ShouldReplacePixelsByAlphaThreshold<TPixel>(threshold);
+
+        TransparentColorMode mode = quantizer.Options.TransparentColorMode;
         bool replaceTransparent = EncodingUtilities.ShouldReplaceTransparentPixels<TPixel>(mode);
 
         IDither? dither = quantizer.Options.Dither;
diff --git a/src/ImageSharp/Processing/Processors/Quantization/WuQuantizer{TPixel}.cs b/src/ImageSharp/Processing/Processors/Quantization/WuQuantizer{TPixel}.cs
index 4b709838ef..03d6ac0da6 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/WuQuantizer{TPixel}.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/WuQuantizer{TPixel}.cs
@@ -6,7 +6,6 @@
 using System.Numerics;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
-using SixLabors.ImageSharp.Formats;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;
 
@@ -107,9 +106,9 @@ public ReadOnlyMemory<TPixel> Palette
     }
 
     /// <inheritdoc/>
-    public readonly void AddPaletteColors(in Buffer2DRegion<TPixel> pixelRegion, TransparentColorMode mode)
+    public readonly void AddPaletteColors(in Buffer2DRegion<TPixel> pixelRegion)
     {
-        PixelRowDelegate pixelRowDelegate = new(ref Unsafe.AsRef(in this), mode);
+        PixelRowDelegate pixelRowDelegate = new(ref Unsafe.AsRef(in this));
         QuantizerUtilities.AddPaletteColors<WuQuantizer<TPixel>, TPixel, Rgba32, PixelRowDelegate>(
             ref Unsafe.AsRef(in this),
             in pixelRegion,
@@ -162,12 +161,7 @@ private void ResolvePalette()
     /// <inheritdoc/>
     [MethodImpl(InliningOptions.ShortMethod)]
     public readonly IndexedImageFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> source, Rectangle bounds)
-        => this.QuantizeFrame(source, bounds, TransparentColorMode.Preserve);
-
-    /// <inheritdoc/>
-    [MethodImpl(InliningOptions.ShortMethod)]
-    public readonly IndexedImageFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> source, Rectangle bounds, TransparentColorMode mode)
-        => QuantizerUtilities.QuantizeFrame(ref Unsafe.AsRef(in this), source, bounds, mode);
+        => QuantizerUtilities.QuantizeFrame(ref Unsafe.AsRef(in this), source, bounds);
 
     /// <inheritdoc/>
     public readonly byte GetQuantizedColor(TPixel color, out TPixel match)
@@ -891,13 +885,7 @@ public override readonly int GetHashCode()
     {
         private readonly WuQuantizer<TPixel> quantizer;
 
-        public PixelRowDelegate(ref WuQuantizer<TPixel> quantizer, TransparentColorMode mode)
-        {
-            this.quantizer = quantizer;
-            this.TransparentColorMode = mode;
-        }
-
-        public TransparentColorMode TransparentColorMode { get; }
+        public PixelRowDelegate(ref WuQuantizer<TPixel> quantizer) => this.quantizer = quantizer;
 
         public void Invoke(ReadOnlySpan<Rgba32> row, int rowIndex) => this.quantizer.Build3DHistogram(row);
     }

From 93f8bdf94f5d4c7d525a1721bb34cddb4c8cdfe4 Mon Sep 17 00:00:00 2001
From: James Jackson-South <james_south@hotmail.com>
Date: Wed, 2 Apr 2025 22:42:47 +1000
Subject: [PATCH 14/18] ImageMagick.NET to GIF encoder benchmark

---
 .../Codecs/Gif/EncodeGif.cs                      | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/tests/ImageSharp.Benchmarks/Codecs/Gif/EncodeGif.cs b/tests/ImageSharp.Benchmarks/Codecs/Gif/EncodeGif.cs
index 2b2428210a..b8f8f78517 100644
--- a/tests/ImageSharp.Benchmarks/Codecs/Gif/EncodeGif.cs
+++ b/tests/ImageSharp.Benchmarks/Codecs/Gif/EncodeGif.cs
@@ -3,6 +3,7 @@
 
 using System.Drawing.Imaging;
 using BenchmarkDotNet.Attributes;
+using ImageMagick;
 using SixLabors.ImageSharp.Formats.Gif;
 using SixLabors.ImageSharp.PixelFormats;
 using SixLabors.ImageSharp.Processing;
@@ -18,6 +19,7 @@ public abstract class EncodeGif
     private FileStream bmpStream;
     private SDImage bmpDrawing;
     private Image<Rgba32> bmpCore;
+    private MagickImageCollection magickImage;
 
     protected abstract GifEncoder Encoder { get; }
 
@@ -29,10 +31,14 @@ public void ReadImages()
     {
         if (this.bmpStream == null)
         {
-            this.bmpStream = File.OpenRead(Path.Combine(TestEnvironment.InputImagesDirectoryFullPath, this.TestImage));
+            string filePath = Path.Combine(TestEnvironment.InputImagesDirectoryFullPath, this.TestImage);
+            this.bmpStream = File.OpenRead(filePath);
             this.bmpCore = Image.Load<Rgba32>(this.bmpStream);
             this.bmpStream.Position = 0;
             this.bmpDrawing = SDImage.FromStream(this.bmpStream);
+
+            this.bmpStream.Position = 0;
+            this.magickImage = new MagickImageCollection(this.bmpStream);
         }
     }
 
@@ -43,6 +49,7 @@ public void Cleanup()
         this.bmpStream = null;
         this.bmpCore.Dispose();
         this.bmpDrawing.Dispose();
+        this.magickImage.Dispose();
     }
 
     [Benchmark(Baseline = true, Description = "System.Drawing Gif")]
@@ -58,6 +65,13 @@ public void GifImageSharp()
         using MemoryStream memoryStream = new();
         this.bmpCore.SaveAsGif(memoryStream, this.Encoder);
     }
+
+    [Benchmark(Description = "Magick.NET Gif")]
+    public void GifMagickNet()
+    {
+        using MemoryStream ms = new();
+        this.magickImage.Write(ms, MagickFormat.Gif);
+    }
 }
 
 public class EncodeGif_DefaultEncoder : EncodeGif

From b989843f181eeae341d28268ebc85aabc352df7d Mon Sep 17 00:00:00 2001
From: James Jackson-South <james_south@hotmail.com>
Date: Sat, 5 Apr 2025 00:40:51 +1000
Subject: [PATCH 15/18] Simplify GifEncoderCore, seal palette quantizers

---
 src/ImageSharp/Formats/Gif/GifEncoderCore.cs  | 216 +++++++-----------
 .../Quantization/WebSafePaletteQuantizer.cs   |   2 +-
 .../Quantization/WernerPaletteQuantizer.cs    |   2 +-
 3 files changed, 90 insertions(+), 130 deletions(-)

diff --git a/src/ImageSharp/Formats/Gif/GifEncoderCore.cs b/src/ImageSharp/Formats/Gif/GifEncoderCore.cs
index c0d74e03e6..43af476f2a 100644
--- a/src/ImageSharp/Formats/Gif/GifEncoderCore.cs
+++ b/src/ImageSharp/Formats/Gif/GifEncoderCore.cs
@@ -9,7 +9,6 @@
 using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.Metadata.Profiles.Xmp;
 using SixLabors.ImageSharp.PixelFormats;
-using SixLabors.ImageSharp.Processing;
 using SixLabors.ImageSharp.Processing.Processors.Quantization;
 
 namespace SixLabors.ImageSharp.Formats.Gif;
@@ -19,6 +18,8 @@ namespace SixLabors.ImageSharp.Formats.Gif;
 /// </summary>
 internal sealed class GifEncoderCore
 {
+    private readonly GifEncoder encoder;
+
     /// <summary>
     /// Used for allocating memory during processing operations.
     /// </summary>
@@ -34,21 +35,6 @@ internal sealed class GifEncoderCore
     /// </summary>
     private readonly bool skipMetadata;
 
-    /// <summary>
-    /// The quantizer used to generate the color palette.
-    /// </summary>
-    private IQuantizer? quantizer;
-
-    /// <summary>
-    /// The fallback quantizer to use when no quantizer is provided.
-    /// </summary>
-    private static readonly IQuantizer FallbackQuantizer = KnownQuantizers.Octree;
-
-    /// <summary>
-    /// Whether the quantizer was supplied via options.
-    /// </summary>
-    private readonly bool hasQuantizer;
-
     /// <summary>
     /// The color table mode: Global or local.
     /// </summary>
@@ -86,9 +72,8 @@ public GifEncoderCore(Configuration configuration, GifEncoder encoder)
     {
         this.configuration = configuration;
         this.memoryAllocator = configuration.MemoryAllocator;
+        this.encoder = encoder;
         this.skipMetadata = encoder.SkipMetadata;
-        this.quantizer = encoder.Quantizer;
-        this.hasQuantizer = encoder.Quantizer is not null;
         this.colorTableMode = encoder.ColorTableMode;
         this.pixelSamplingStrategy = encoder.PixelSamplingStrategy;
         this.backgroundColor = encoder.BackgroundColor;
@@ -124,64 +109,64 @@ public void Encode<TPixel>(Image<TPixel> image, Stream stream, CancellationToken
 
         // Quantize the first image frame returning a palette.
         IndexedImageFrame<TPixel>? quantized = null;
-        if (this.quantizer is null)
+        IQuantizer? globalQuantizer = this.encoder.Quantizer;
+        TransparentColorMode mode = this.transparentColorMode;
+
+        // Create a new quantizer options instance augmenting the transparent color mode to match the encoder.
+        QuantizerOptions options = (this.encoder.Quantizer?.Options ?? new()).DeepClone(o => o.TransparentColorMode = mode);
+
+        if (globalQuantizer is null)
         {
             // Is this a gif with color information. If so use that, otherwise use octree.
             if (gifMetadata.ColorTableMode == FrameColorTableMode.Global && gifMetadata.GlobalColorTable?.Length > 0)
             {
-                // We avoid dithering by default to preserve the original colors.
                 int transparencyIndex = GetTransparentIndex(quantized, frameMetadata);
                 if (transparencyIndex >= 0 || gifMetadata.GlobalColorTable.Value.Length < 256)
                 {
-                    this.quantizer = new PaletteQuantizer(gifMetadata.GlobalColorTable.Value, new() { Dither = null });
+                    // We avoid dithering by default to preserve the original colors.
+                    globalQuantizer = new PaletteQuantizer(gifMetadata.GlobalColorTable.Value, options.DeepClone(o => o.Dither = null));
                 }
                 else
                 {
-                    this.quantizer = FallbackQuantizer;
+                    globalQuantizer = new OctreeQuantizer(options);
                 }
             }
             else
             {
-                this.quantizer = FallbackQuantizer;
+                globalQuantizer = new OctreeQuantizer(options);
             }
         }
 
-        // Create a new quantizer options instance augmenting the transparent color mode to match the encoder.
-        TransparentColorMode mode = this.transparentColorMode;
-        QuantizerOptions options = this.quantizer.Options.DeepClone(o => o.TransparentColorMode = mode);
-
         // Quantize the first frame.
-        using (IQuantizer<TPixel> frameQuantizer = this.quantizer.CreatePixelSpecificQuantizer<TPixel>(this.configuration, options))
-        {
-            IPixelSamplingStrategy strategy = this.pixelSamplingStrategy;
+        IPixelSamplingStrategy strategy = this.pixelSamplingStrategy;
 
-            ImageFrame<TPixel> encodingFrame = image.Frames.RootFrame;
-            if (useGlobalTableForFirstFrame)
+        ImageFrame<TPixel> encodingFrame = image.Frames.RootFrame;
+        if (useGlobalTableForFirstFrame)
+        {
+            using IQuantizer<TPixel> firstFrameQuantizer = globalQuantizer.CreatePixelSpecificQuantizer<TPixel>(this.configuration, options);
+            if (useGlobalTable)
             {
-                if (useGlobalTable)
-                {
-                    frameQuantizer.BuildPalette(strategy, image);
-                    quantized = frameQuantizer.QuantizeFrame(encodingFrame, image.Bounds);
-                }
-                else
-                {
-                    frameQuantizer.BuildPalette(strategy, encodingFrame);
-                    quantized = frameQuantizer.QuantizeFrame(encodingFrame, encodingFrame.Bounds);
-                }
+                firstFrameQuantizer.BuildPalette(strategy, image);
             }
             else
             {
-                quantized = this.QuantizeAdditionalFrameAndUpdateMetadata(
-                    encodingFrame,
-                    options,
-                    encodingFrame.Bounds,
-                    frameMetadata,
-                    true,
-                    default,
-                    false,
-                    frameMetadata.HasTransparency ? frameMetadata.TransparencyIndex : -1,
-                    Color.Transparent);
+                firstFrameQuantizer.BuildPalette(strategy, encodingFrame);
             }
+
+            quantized = firstFrameQuantizer.QuantizeFrame(encodingFrame, encodingFrame.Bounds);
+        }
+        else
+        {
+            quantized = this.QuantizeFrameAndUpdateMetadata(
+                encodingFrame,
+                globalQuantizer,
+                default,
+                encodingFrame.Bounds,
+                frameMetadata,
+                true,
+                false,
+                frameMetadata.HasTransparency ? frameMetadata.TransparencyIndex : -1,
+                Color.Transparent);
         }
 
         // Write the header.
@@ -231,14 +216,18 @@ public void Encode<TPixel>(Image<TPixel> image, Stream stream, CancellationToken
             // Capture the global palette for reuse on subsequent frames and cleanup the quantized frame.
             TPixel[] globalPalette = image.Frames.Count == 1 ? [] : quantized.Palette.ToArray();
 
-            this.EncodeAdditionalFrames(
-                stream,
-                image,
-                options,
-                globalPalette,
-                derivedTransparencyIndex,
-                frameMetadata.DisposalMode,
-                cancellationToken);
+            if (image.Frames.Count > 1)
+            {
+                using PaletteQuantizer<TPixel> globalFrameQuantizer = new(this.configuration, globalQuantizer.Options, quantized.Palette.ToArray());
+                this.EncodeAdditionalFrames(
+                    stream,
+                    image,
+                    globalQuantizer,
+                    globalFrameQuantizer,
+                    derivedTransparencyIndex,
+                    frameMetadata.DisposalMode,
+                    cancellationToken);
+            }
         }
         finally
         {
@@ -264,70 +253,43 @@ private static GifFrameMetadata GetGifFrameMetadata<TPixel>(ImageFrame<TPixel> f
     private void EncodeAdditionalFrames<TPixel>(
         Stream stream,
         Image<TPixel> image,
-        QuantizerOptions options,
-        ReadOnlyMemory<TPixel> globalPalette,
+        IQuantizer globalQuantizer,
+        PaletteQuantizer<TPixel> globalFrameQuantizer,
         int globalTransparencyIndex,
         FrameDisposalMode previousDisposalMode,
         CancellationToken cancellationToken)
         where TPixel : unmanaged, IPixel<TPixel>
     {
-        if (image.Frames.Count == 1)
-        {
-            return;
-        }
-
-        PaletteQuantizer<TPixel> globalPaletteQuantizer = default;
-        bool hasGlobalPaletteQuantizer = false;
-
         // Store the first frame as a reference for de-duplication comparison.
         ImageFrame<TPixel> previousFrame = image.Frames.RootFrame;
 
         // This frame is reused to store de-duplicated pixel buffers.
         using ImageFrame<TPixel> encodingFrame = new(previousFrame.Configuration, previousFrame.Size);
 
-        try
+        for (int i = 1; i < image.Frames.Count; i++)
         {
-            for (int i = 1; i < image.Frames.Count; i++)
-            {
-                cancellationToken.ThrowIfCancellationRequested();
+            cancellationToken.ThrowIfCancellationRequested();
 
-                // Gather the metadata for this frame.
-                ImageFrame<TPixel> currentFrame = image.Frames[i];
-                ImageFrame<TPixel>? nextFrame = i < image.Frames.Count - 1 ? image.Frames[i + 1] : null;
-                GifFrameMetadata gifMetadata = GetGifFrameMetadata(currentFrame, globalTransparencyIndex);
-                bool useLocal = this.colorTableMode == FrameColorTableMode.Local || (gifMetadata.ColorTableMode == FrameColorTableMode.Local);
+            // Gather the metadata for this frame.
+            ImageFrame<TPixel> currentFrame = image.Frames[i];
+            ImageFrame<TPixel>? nextFrame = i < image.Frames.Count - 1 ? image.Frames[i + 1] : null;
+            GifFrameMetadata gifMetadata = GetGifFrameMetadata(currentFrame, globalTransparencyIndex);
+            bool useLocal = this.colorTableMode == FrameColorTableMode.Local || (gifMetadata.ColorTableMode == FrameColorTableMode.Local);
 
-                if (!useLocal && !hasGlobalPaletteQuantizer && i > 0)
-                {
-                    // The palette quantizer can reuse the same global pixel map across multiple frames since the palette is unchanging.
-                    // This allows a reduction of memory usage across multi-frame gifs using a global palette
-                    // and also allows use to reuse the cache from previous runs.
-                    globalPaletteQuantizer = new(this.configuration, options, globalPalette);
-                    hasGlobalPaletteQuantizer = true;
-                }
+            this.EncodeAdditionalFrame(
+                stream,
+                previousFrame,
+                currentFrame,
+                nextFrame,
+                encodingFrame,
+                globalQuantizer,
+                globalFrameQuantizer,
+                useLocal,
+                gifMetadata,
+                previousDisposalMode);
 
-                this.EncodeAdditionalFrame(
-                    stream,
-                    previousFrame,
-                    currentFrame,
-                    nextFrame,
-                    encodingFrame,
-                    options,
-                    useLocal,
-                    gifMetadata,
-                    globalPaletteQuantizer,
-                    previousDisposalMode);
-
-                previousFrame = currentFrame;
-                previousDisposalMode = gifMetadata.DisposalMode;
-            }
-        }
-        finally
-        {
-            if (hasGlobalPaletteQuantizer)
-            {
-                globalPaletteQuantizer.Dispose();
-            }
+            previousFrame = currentFrame;
+            previousDisposalMode = gifMetadata.DisposalMode;
         }
     }
 
@@ -363,10 +325,10 @@ private void EncodeAdditionalFrame<TPixel>(
         ImageFrame<TPixel> currentFrame,
         ImageFrame<TPixel>? nextFrame,
         ImageFrame<TPixel> encodingFrame,
-        QuantizerOptions options,
+        IQuantizer globalQuantizer,
+        PaletteQuantizer<TPixel> globalFrameQuantizer,
         bool useLocal,
         GifFrameMetadata metadata,
-        PaletteQuantizer<TPixel> globalPaletteQuantizer,
         FrameDisposalMode previousDisposalMode)
         where TPixel : unmanaged, IPixel<TPixel>
     {
@@ -393,13 +355,13 @@ private void EncodeAdditionalFrame<TPixel>(
                 background,
                 true);
 
-        using IndexedImageFrame<TPixel> quantized = this.QuantizeAdditionalFrameAndUpdateMetadata(
+        using IndexedImageFrame<TPixel> quantized = this.QuantizeFrameAndUpdateMetadata(
                 encodingFrame,
-                options,
+                globalQuantizer,
+                globalFrameQuantizer,
                 bounds,
                 metadata,
                 useLocal,
-                globalPaletteQuantizer,
                 difference,
                 transparencyIndex,
                 background);
@@ -418,13 +380,13 @@ private void EncodeAdditionalFrame<TPixel>(
         this.WriteImageData(indices, stream, quantized.Palette.Length, metadata.TransparencyIndex);
     }
 
-    private IndexedImageFrame<TPixel> QuantizeAdditionalFrameAndUpdateMetadata<TPixel>(
+    private IndexedImageFrame<TPixel> QuantizeFrameAndUpdateMetadata<TPixel>(
         ImageFrame<TPixel> encodingFrame,
-        QuantizerOptions options,
+        IQuantizer globalQuantizer,
+        PaletteQuantizer<TPixel> globalFrameQuantizer,
         Rectangle bounds,
         GifFrameMetadata metadata,
         bool useLocal,
-        PaletteQuantizer<TPixel> globalPaletteQuantizer,
         bool hasDuplicates,
         int transparencyIndex,
         Color transparentColor)
@@ -451,20 +413,19 @@ private IndexedImageFrame<TPixel> QuantizeAdditionalFrameAndUpdateMetadata<TPixe
                         transparencyIndex = palette.Length;
                         metadata.TransparencyIndex = ClampIndex(transparencyIndex);
 
-                        QuantizerOptions paletteOptions = options.DeepClone(o =>
+                        QuantizerOptions options = globalQuantizer.Options.DeepClone(o =>
                         {
                             o.MaxColors = palette.Length;
                             o.Dither = null;
                         });
-                        PaletteQuantizer quantizer = new(palette, paletteOptions, transparencyIndex, transparentColor);
-                        using IQuantizer<TPixel> frameQuantizer = quantizer.CreatePixelSpecificQuantizer<TPixel>(this.configuration, quantizer.Options);
+                        PaletteQuantizer quantizer = new(palette, options, transparencyIndex, transparentColor);
+                        using IQuantizer<TPixel> frameQuantizer = quantizer.CreatePixelSpecificQuantizer<TPixel>(this.configuration);
                         quantized = frameQuantizer.BuildPaletteAndQuantizeFrame(encodingFrame, bounds);
                     }
                     else
                     {
                         // We must quantize the frame to generate a local color table.
-                        IQuantizer quantizer = this.hasQuantizer ? this.quantizer! : FallbackQuantizer;
-                        using IQuantizer<TPixel> frameQuantizer = quantizer.CreatePixelSpecificQuantizer<TPixel>(this.configuration, options);
+                        using IQuantizer<TPixel> frameQuantizer = globalQuantizer.CreatePixelSpecificQuantizer<TPixel>(this.configuration);
                         quantized = frameQuantizer.BuildPaletteAndQuantizeFrame(encodingFrame, bounds);
 
                         // The transparency index derived by the quantizer will differ from the index
@@ -476,7 +437,7 @@ private IndexedImageFrame<TPixel> QuantizeAdditionalFrameAndUpdateMetadata<TPixe
                 else
                 {
                     // Just use the local palette.
-                    QuantizerOptions paletteOptions = options.DeepClone(o =>
+                    QuantizerOptions paletteOptions = globalQuantizer.Options.DeepClone(o =>
                     {
                         o.MaxColors = palette.Length;
                         o.Dither = null;
@@ -489,8 +450,7 @@ private IndexedImageFrame<TPixel> QuantizeAdditionalFrameAndUpdateMetadata<TPixe
             else
             {
                 // We must quantize the frame to generate a local color table.
-                IQuantizer quantizer = this.hasQuantizer ? this.quantizer! : FallbackQuantizer;
-                using IQuantizer<TPixel> frameQuantizer = quantizer.CreatePixelSpecificQuantizer<TPixel>(this.configuration, options);
+                using IQuantizer<TPixel> frameQuantizer = globalQuantizer.CreatePixelSpecificQuantizer<TPixel>(this.configuration);
                 quantized = frameQuantizer.BuildPaletteAndQuantizeFrame(encodingFrame, bounds);
 
                 // The transparency index derived by the quantizer might differ from the index
@@ -520,12 +480,12 @@ private IndexedImageFrame<TPixel> QuantizeAdditionalFrameAndUpdateMetadata<TPixe
             if (hasDuplicates && !metadata.HasTransparency)
             {
                 metadata.HasTransparency = true;
-                transparencyIndex = globalPaletteQuantizer.Palette.Length;
+                transparencyIndex = globalFrameQuantizer.Palette.Length;
                 metadata.TransparencyIndex = ClampIndex(transparencyIndex);
             }
 
-            globalPaletteQuantizer.SetTransparencyIndex(transparencyIndex, transparentColor.ToPixel<TPixel>());
-            quantized = globalPaletteQuantizer.QuantizeFrame(encodingFrame, bounds);
+            globalFrameQuantizer.SetTransparencyIndex(transparencyIndex, transparentColor.ToPixel<TPixel>());
+            quantized = globalFrameQuantizer.QuantizeFrame(encodingFrame, bounds);
         }
 
         return quantized;
diff --git a/src/ImageSharp/Processing/Processors/Quantization/WebSafePaletteQuantizer.cs b/src/ImageSharp/Processing/Processors/Quantization/WebSafePaletteQuantizer.cs
index 604cae6681..fa1763367c 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/WebSafePaletteQuantizer.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/WebSafePaletteQuantizer.cs
@@ -6,7 +6,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization;
 /// <summary>
 /// A palette quantizer consisting of web safe colors as defined in the CSS Color Module Level 4.
 /// </summary>
-public class WebSafePaletteQuantizer : PaletteQuantizer
+public sealed class WebSafePaletteQuantizer : PaletteQuantizer
 {
     /// <summary>
     /// Initializes a new instance of the <see cref="WebSafePaletteQuantizer" /> class.
diff --git a/src/ImageSharp/Processing/Processors/Quantization/WernerPaletteQuantizer.cs b/src/ImageSharp/Processing/Processors/Quantization/WernerPaletteQuantizer.cs
index 023ee7f2e0..cd7b80e81d 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/WernerPaletteQuantizer.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/WernerPaletteQuantizer.cs
@@ -7,7 +7,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization;
 /// A palette quantizer consisting of colors as defined in the original second edition of Werner’s Nomenclature of Colours 1821.
 /// The hex codes were collected and defined by Nicholas Rougeux <see href="https://www.c82.net/werner"/>
 /// </summary>
-public class WernerPaletteQuantizer : PaletteQuantizer
+public sealed class WernerPaletteQuantizer : PaletteQuantizer
 {
     /// <summary>
     /// Initializes a new instance of the <see cref="WernerPaletteQuantizer" /> class.

From b09ea4104231081d67b267efb95817d4f8aecddb Mon Sep 17 00:00:00 2001
From: James Jackson-South <james_south@hotmail.com>
Date: Mon, 28 Apr 2025 15:43:27 +1000
Subject: [PATCH 16/18] Fix build

---
 src/ImageSharp/ImageSharp.csproj                | 5 -----
 tests/ImageSharp.Tests/Image/ImageFrameTests.cs | 2 +-
 tests/ImageSharp.Tests/Image/ImageTests.cs      | 2 +-
 3 files changed, 2 insertions(+), 7 deletions(-)

diff --git a/src/ImageSharp/ImageSharp.csproj b/src/ImageSharp/ImageSharp.csproj
index 36c9375bd6..71dd4c8fb2 100644
--- a/src/ImageSharp/ImageSharp.csproj
+++ b/src/ImageSharp/ImageSharp.csproj
@@ -44,11 +44,6 @@
     <None Include="..\..\LICENSE" Pack="true" PackagePath="" />
     <None Include="..\..\shared-infrastructure\branding\icons\imagesharp\sixlabors.imagesharp.128.png" Pack="true" PackagePath="" />
     <None Include="..\..\SixLabors.ImageSharp.props" Pack="true" PackagePath="build" />
-    <None Include="Common\InlineArray.cs">
-      <DesignTime>True</DesignTime>
-      <AutoGen>True</AutoGen>
-      <DependentUpon>InlineArray.tt</DependentUpon>
-    </None>
   </ItemGroup>
 
   <ItemGroup>
diff --git a/tests/ImageSharp.Tests/Image/ImageFrameTests.cs b/tests/ImageSharp.Tests/Image/ImageFrameTests.cs
index d46385e0a2..ef5b5f4def 100644
--- a/tests/ImageSharp.Tests/Image/ImageFrameTests.cs
+++ b/tests/ImageSharp.Tests/Image/ImageFrameTests.cs
@@ -119,7 +119,7 @@ public void CopyPixelDataTo_Success(bool disco, bool byteSpan)
             }
             else
             {
-                Span<La16> destination = MemoryMarshal.Cast<byte, La16>(actual.AsSpan());
+                Span<La16> destination = MemoryMarshal.Cast<byte, La16>(actual);
                 image.Frames.RootFrame.CopyPixelDataTo(destination);
             }
 
diff --git a/tests/ImageSharp.Tests/Image/ImageTests.cs b/tests/ImageSharp.Tests/Image/ImageTests.cs
index ff0abd8c2b..16b8962c70 100644
--- a/tests/ImageSharp.Tests/Image/ImageTests.cs
+++ b/tests/ImageSharp.Tests/Image/ImageTests.cs
@@ -197,7 +197,7 @@ public void CopyPixelDataTo_Success(bool disco, bool byteSpan)
             }
             else
             {
-                Span<La16> destination = MemoryMarshal.Cast<byte, La16>(actual.AsSpan());
+                Span<La16> destination = MemoryMarshal.Cast<byte, La16>(actual);
                 image.CopyPixelDataTo(destination);
             }
 

From a99e6cf3800391b2b763b80a09f145c63d8813c5 Mon Sep 17 00:00:00 2001
From: James Jackson-South <james_south@hotmail.com>
Date: Tue, 29 Apr 2025 20:53:33 +1000
Subject: [PATCH 17/18] Revert to original CoarseCache

---
 .../Quantization/IColorIndexCache.cs          | 84 ++++++++++++++++++-
 1 file changed, 81 insertions(+), 3 deletions(-)

diff --git a/src/ImageSharp/Processing/Processors/Quantization/IColorIndexCache.cs b/src/ImageSharp/Processing/Processors/Quantization/IColorIndexCache.cs
index 4e4fa5f0ac..e4f6c87839 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/IColorIndexCache.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/IColorIndexCache.cs
@@ -119,6 +119,84 @@ public void Dispose()
     }
 }
 
+/// <summary>
+/// A coarse cache for color distance lookups that uses a fixed-size lookup table.
+/// </summary>
+/// <remarks>
+/// This cache uses a fixed lookup table with 2,097,152 bins, each storing a 2-byte value,
+/// resulting in a worst-case memory usage of approximately 4 MB. Lookups and insertions are
+/// performed in constant time (O(1)) via direct table indexing. This design is optimized for
+/// speed while maintaining a predictable, fixed memory footprint.
+/// </remarks>
+internal unsafe struct CoarseCache : IColorIndexCache<CoarseCache>
+{
+    private const int IndexRBits = 5;
+    private const int IndexGBits = 5;
+    private const int IndexBBits = 5;
+    private const int IndexABits = 6;
+    private const int IndexRCount = 1 << IndexRBits; // 32 bins for red
+    private const int IndexGCount = 1 << IndexGBits; // 32 bins for green
+    private const int IndexBCount = 1 << IndexBBits; // 32 bins for blue
+    private const int IndexACount = 1 << IndexABits; // 64 bins for alpha
+    private const int TotalBins = IndexRCount * IndexGCount * IndexBCount * IndexACount; // 2,097,152 bins
+
+    private readonly IMemoryOwner<short> binsOwner;
+    private readonly short* binsPointer;
+    private MemoryHandle binsHandle;
+
+    private CoarseCache(MemoryAllocator allocator)
+    {
+        this.binsOwner = allocator.Allocate<short>(TotalBins);
+        this.binsOwner.GetSpan().Fill(-1);
+        this.binsHandle = this.binsOwner.Memory.Pin();
+        this.binsPointer = (short*)this.binsHandle.Pointer;
+    }
+
+    /// <inheritdoc/>
+    public static CoarseCache Create(MemoryAllocator allocator) => new(allocator);
+
+    /// <inheritdoc/>
+    [MethodImpl(InliningOptions.ShortMethod)]
+    public readonly bool TryAdd(Rgba32 color, short value)
+    {
+        this.binsPointer[GetCoarseIndex(color)] = value;
+        return true;
+    }
+
+    /// <inheritdoc/>
+    [MethodImpl(InliningOptions.ShortMethod)]
+    public readonly bool TryGetValue(Rgba32 color, out short value)
+    {
+        value = this.binsPointer[GetCoarseIndex(color)];
+        return value > -1; // Coarse match found
+    }
+
+    [MethodImpl(InliningOptions.ShortMethod)]
+    private static int GetCoarseIndex(Rgba32 color)
+    {
+        int rIndex = color.R >> (8 - IndexRBits);
+        int gIndex = color.G >> (8 - IndexGBits);
+        int bIndex = color.B >> (8 - IndexBBits);
+        int aIndex = color.A >> (8 - IndexABits);
+
+        return (aIndex * IndexRCount * IndexGCount * IndexBCount) +
+               (rIndex * IndexGCount * IndexBCount) +
+               (gIndex * IndexBCount) +
+               bIndex;
+    }
+
+    /// <inheritdoc/>
+    public readonly void Clear()
+        => this.binsOwner.GetSpan().Fill(-1);
+
+    /// <inheritdoc/>
+    public void Dispose()
+    {
+        this.binsHandle.Dispose();
+        this.binsOwner.Dispose();
+    }
+}
+
 /// <summary>
 /// <para>
 /// CoarseCache is a fast, low-memory lookup structure for caching palette indices associated with RGBA values,
@@ -147,7 +225,7 @@ public void Dispose()
 /// making it ideal for applications such as color distance caching in images with a limited palette (up to 256 entries).
 /// </para>
 /// </summary>
-internal unsafe struct CoarseCache : IColorIndexCache<CoarseCache>
+internal unsafe struct CoarseCacheLite : IColorIndexCache<CoarseCacheLite>
 {
     // Use 5 bits per channel for R, G, and B: 32 levels each.
     // Total buckets = 32^3 = 32768.
@@ -158,7 +236,7 @@ internal unsafe struct CoarseCache : IColorIndexCache<CoarseCache>
     private readonly AlphaBucket* buckets;
     private MemoryHandle bucketHandle;
 
-    private CoarseCache(MemoryAllocator allocator)
+    private CoarseCacheLite(MemoryAllocator allocator)
     {
         this.bucketsOwner = allocator.Allocate<AlphaBucket>(BucketCount, AllocationOptions.Clean);
         this.bucketHandle = this.bucketsOwner.Memory.Pin();
@@ -166,7 +244,7 @@ private CoarseCache(MemoryAllocator allocator)
     }
 
     /// <inheritdoc/>
-    public static CoarseCache Create(MemoryAllocator allocator) => new(allocator);
+    public static CoarseCacheLite Create(MemoryAllocator allocator) => new(allocator);
 
     /// <inheritdoc/>
     public readonly bool TryAdd(Rgba32 color, short paletteIndex)

From 583d89e7bdf4e811cf63458c94db68992ba67881 Mon Sep 17 00:00:00 2001
From: James Jackson-South <james_south@hotmail.com>
Date: Wed, 30 Apr 2025 12:21:35 +1000
Subject: [PATCH 18/18] Update ref images, tweak lite cache to match original
 (unused)

---
 src/ImageSharp/Common/InlineArray.cs          |  9 ++++++++
 src/ImageSharp/Common/InlineArray.tt          |  2 +-
 .../Quantization/IColorIndexCache.cs          | 22 +++++++++----------
 ...rInBox_Rgba32_CalliphoraPartial - Copy.png |  3 +++
 ...erFilterInBox_Rgba32_CalliphoraPartial.png |  4 ++--
 ..._WorksWithAllDitherers_Bike_Bayer16x16.png |  4 ++--
 ...er_WorksWithAllDitherers_Bike_Bayer4x4.png |  4 ++--
 ...er_WorksWithAllDitherers_Bike_Bayer8x8.png |  4 ++--
 ..._WorksWithAllDitherers_Bike_Ordered3x3.png |  4 ++--
 ...Ditherers_CalliphoraPartial_Bayer16x16.png |  4 ++--
 ...llDitherers_CalliphoraPartial_Bayer4x4.png |  4 ++--
 ...llDitherers_CalliphoraPartial_Bayer8x8.png |  4 ++--
 ...Ditherers_CalliphoraPartial_Ordered3x3.png |  4 ++--
 ...zed_Encode_Artifacts_Rgba32_issue_2469.png |  4 ++--
 ...antized_Encode_Alpha_Rgba32_Issue_2668.png |  4 ++--
 ...Box_Bike_OctreeQuantizer_OrderedDither.png |  4 ++--
 ..._WebSafePaletteQuantizer_OrderedDither.png |  4 ++--
 ...e_WernerPaletteQuantizer_OrderedDither.png |  4 ++--
 ...onInBox_Bike_WuQuantizer_OrderedDither.png |  4 ++--
 ...aPartial_OctreeQuantizer_OrderedDither.png |  4 ++--
 ..._WebSafePaletteQuantizer_OrderedDither.png |  4 ++--
 ...l_WernerPaletteQuantizer_OrderedDither.png |  4 ++--
 ...phoraPartial_WuQuantizer_OrderedDither.png |  4 ++--
 ...vid_OctreeQuantizer_OrderedDither_0.75.png |  4 ++--
 ..._david_OctreeQuantizer_OrderedDither_1.png |  4 ++--
 ...afePaletteQuantizer_OrderedDither_0.75.png |  4 ++--
 ...ebSafePaletteQuantizer_OrderedDither_1.png |  4 ++--
 ...rnerPaletteQuantizer_OrderedDither_0.5.png |  4 ++--
 ...nerPaletteQuantizer_OrderedDither_0.75.png |  4 ++--
 ...WernerPaletteQuantizer_OrderedDither_1.png |  4 ++--
 ...le_david_WuQuantizer_OrderedDither_0.5.png |  4 ++--
 ...e_david_WuQuantizer_OrderedDither_0.75.png |  4 ++--
 ...cale_david_WuQuantizer_OrderedDither_1.png |  4 ++--
 ...ion_Bike_OctreeQuantizer_OrderedDither.png |  4 ++--
 ..._WebSafePaletteQuantizer_OrderedDither.png |  4 ++--
 ...e_WernerPaletteQuantizer_OrderedDither.png |  4 ++--
 ...ization_Bike_WuQuantizer_OrderedDither.png |  4 ++--
 ...aPartial_OctreeQuantizer_OrderedDither.png |  4 ++--
 ..._WebSafePaletteQuantizer_OrderedDither.png |  4 ++--
 ...l_WernerPaletteQuantizer_OrderedDither.png |  4 ++--
 ...phoraPartial_WuQuantizer_OrderedDither.png |  4 ++--
 41 files changed, 98 insertions(+), 86 deletions(-)
 create mode 100644 tests/Images/External/ReferenceOutput/DitherTests/ApplyDitherFilterInBox_Rgba32_CalliphoraPartial - Copy.png

diff --git a/src/ImageSharp/Common/InlineArray.cs b/src/ImageSharp/Common/InlineArray.cs
index 358121d0a4..c20c0d8750 100644
--- a/src/ImageSharp/Common/InlineArray.cs
+++ b/src/ImageSharp/Common/InlineArray.cs
@@ -17,6 +17,15 @@ internal struct InlineArray4<T>
     private T t;
 }
 
+/// <summary>
+/// Represents a safe, fixed sized buffer of 8 elements.
+/// </summary>
+[InlineArray(8)]
+internal struct InlineArray8<T>
+{
+    private T t;
+}
+
 /// <summary>
 /// Represents a safe, fixed sized buffer of 16 elements.
 /// </summary>
diff --git a/src/ImageSharp/Common/InlineArray.tt b/src/ImageSharp/Common/InlineArray.tt
index fae6ab2279..ab488591a7 100644
--- a/src/ImageSharp/Common/InlineArray.tt
+++ b/src/ImageSharp/Common/InlineArray.tt
@@ -16,7 +16,7 @@ namespace SixLabors.ImageSharp;
 <#GenerateInlineArrays();#>
 
 <#+
-private static int[] Lengths = new int[] {4, 16 };
+private static int[] Lengths = new int[] {4, 8, 16 };
 
 void GenerateInlineArrays()
 {
diff --git a/src/ImageSharp/Processing/Processors/Quantization/IColorIndexCache.cs b/src/ImageSharp/Processing/Processors/Quantization/IColorIndexCache.cs
index e4f6c87839..32d95137bc 100644
--- a/src/ImageSharp/Processing/Processors/Quantization/IColorIndexCache.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/IColorIndexCache.cs
@@ -124,7 +124,7 @@ public void Dispose()
 /// </summary>
 /// <remarks>
 /// This cache uses a fixed lookup table with 2,097,152 bins, each storing a 2-byte value,
-/// resulting in a worst-case memory usage of approximately 4 MB. Lookups and insertions are
+/// resulting in a memory usage of approximately 4 MB. Lookups and insertions are
 /// performed in constant time (O(1)) via direct table indexing. This design is optimized for
 /// speed while maintaining a predictable, fixed memory footprint.
 /// </remarks>
@@ -209,16 +209,16 @@ public void Dispose()
 /// </para>
 /// <para>
 /// Performance Characteristics:
-///   - Lookup: O(1) for computing the bucket index from the RGB channels, plus a small constant time (up to 4 iterations)
+///   - Lookup: O(1) for computing the bucket index from the RGB channels, plus a small constant time (up to 8 iterations)
 ///     to search through the alpha entries in the bucket.
 ///   - Insertion: O(1) for bucket index computation and a quick linear search over a very small (fixed) number of entries.
 /// </para>
 /// <para>
 /// Memory Characteristics:
 ///   - The cache consists of 32,768 buckets.
-///   - Each <see cref="AlphaBucket"/> is implemented using an inline array with a capacity of 4 entries.
-///   - Each bucket occupies approximately 18 bytes.
-///   - Overall, the buckets occupy roughly 32,768 × 18 = 589,824 bytes (576 KB).
+///   - Each <see cref="AlphaBucket"/> is implemented using an inline array with a capacity of 8 entries.
+///   - Each bucket occupies approximately 1 byte (Count) + (8 entries × 3 bytes each) ≈ 25 bytes.
+///   - Overall, the buckets occupy roughly 32,768 × 25 bytes = 819,200 bytes (≈ 800 KB).
 /// </para>
 /// <para>
 /// This design provides nearly constant-time lookup and insertion with minimal memory usage,
@@ -304,27 +304,27 @@ public struct AlphaEntry
     public struct AlphaBucket
     {
         // Fixed capacity for alpha entries in this bucket.
-        // We choose a capacity of 4 for several reasons:
+        // We choose a capacity of 8 for several reasons:
         //
         // 1. The alpha channel is quantized to 6 bits, so there are 64 possible distinct values.
         //    In the worst-case, a given RGB bucket might encounter up to 64 different alpha values.
         //
         // 2. However, in practice (based on probability theory and typical image data),
         //    the number of unique alpha values that actually occur for a given quantized RGB
-        //    bucket is usually very small. If you randomly sample 4 values out of 64,
+        //    bucket is usually very small. If you randomly sample 8 values out of 64,
         //    the probability that these 4 samples are all unique is high if the distribution
         //    of alpha values is skewed or if only a few alpha values are used.
         //
         // 3. Statistically, for many real-world images, most RGB buckets will have only a couple
-        //    of unique alpha values. Allocating 4 slots per bucket provides a good trade-off:
+        //    of unique alpha values. Allocating 8 slots per bucket provides a good trade-off:
         //    it captures the common-case scenario while keeping overall memory usage low.
         //
-        // 4. Even if more than 4 unique alpha values occur in a bucket,
+        // 4. Even if more than 8 unique alpha values occur in a bucket,
         //    our design overwrites the first entry. This behavior gives us some "wriggle room"
         //    while preserving the most frequently encountered or most recent values.
-        public const int Capacity = 4;
+        public const int Capacity = 8;
         public byte Count;
-        private InlineArray4<AlphaEntry> entries;
+        private InlineArray8<AlphaEntry> entries;
 
         [MethodImpl(InliningOptions.ShortMethod)]
         public bool TryGetValue(byte quantizedAlpha, out short paletteIndex)
diff --git a/tests/Images/External/ReferenceOutput/DitherTests/ApplyDitherFilterInBox_Rgba32_CalliphoraPartial - Copy.png b/tests/Images/External/ReferenceOutput/DitherTests/ApplyDitherFilterInBox_Rgba32_CalliphoraPartial - Copy.png
new file mode 100644
index 0000000000..43e414da6d
--- /dev/null
+++ b/tests/Images/External/ReferenceOutput/DitherTests/ApplyDitherFilterInBox_Rgba32_CalliphoraPartial - Copy.png	
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:a899a84c6af24bfad89f9fde75957c7a979d65bcf096ab667cb976efd71cb560
+size 271171
diff --git a/tests/Images/External/ReferenceOutput/DitherTests/ApplyDitherFilterInBox_Rgba32_CalliphoraPartial.png b/tests/Images/External/ReferenceOutput/DitherTests/ApplyDitherFilterInBox_Rgba32_CalliphoraPartial.png
index 35ed6dee46..43e414da6d 100644
--- a/tests/Images/External/ReferenceOutput/DitherTests/ApplyDitherFilterInBox_Rgba32_CalliphoraPartial.png
+++ b/tests/Images/External/ReferenceOutput/DitherTests/ApplyDitherFilterInBox_Rgba32_CalliphoraPartial.png
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:a025a094c285cea8510430b0e3657bc59231b38132781e298d60a74238879912
-size 270699
+oid sha256:a899a84c6af24bfad89f9fde75957c7a979d65bcf096ab667cb976efd71cb560
+size 271171
diff --git a/tests/Images/External/ReferenceOutput/DitherTests/DitherFilter_WorksWithAllDitherers_Bike_Bayer16x16.png b/tests/Images/External/ReferenceOutput/DitherTests/DitherFilter_WorksWithAllDitherers_Bike_Bayer16x16.png
index 53b8e40263..e899ffb42a 100644
--- a/tests/Images/External/ReferenceOutput/DitherTests/DitherFilter_WorksWithAllDitherers_Bike_Bayer16x16.png
+++ b/tests/Images/External/ReferenceOutput/DitherTests/DitherFilter_WorksWithAllDitherers_Bike_Bayer16x16.png
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:abdb8fd09b6925a8922f091ee441eaa0f7f81debba9e303c38b7d40bd9fd8479
-size 44173
+oid sha256:ca70bb0200776efd00c4ef7596d4e1f2f5fbc68e447b395b25ef2b3c732e5156
+size 44189
diff --git a/tests/Images/External/ReferenceOutput/DitherTests/DitherFilter_WorksWithAllDitherers_Bike_Bayer4x4.png b/tests/Images/External/ReferenceOutput/DitherTests/DitherFilter_WorksWithAllDitherers_Bike_Bayer4x4.png
index d3a8eddd84..fec3c9b2b3 100644
--- a/tests/Images/External/ReferenceOutput/DitherTests/DitherFilter_WorksWithAllDitherers_Bike_Bayer4x4.png
+++ b/tests/Images/External/ReferenceOutput/DitherTests/DitherFilter_WorksWithAllDitherers_Bike_Bayer4x4.png
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:22725614ba3367b155ed7745034e84c624ed0d4c9b86a4eaa8bf650cc3e5e68f
-size 44345
+oid sha256:20e80e7d9e68fd85bfbc63c61953327354b0634000ec142e01a42618995fd14c
+size 44391
diff --git a/tests/Images/External/ReferenceOutput/DitherTests/DitherFilter_WorksWithAllDitherers_Bike_Bayer8x8.png b/tests/Images/External/ReferenceOutput/DitherTests/DitherFilter_WorksWithAllDitherers_Bike_Bayer8x8.png
index 2a3e95c169..68a95a0540 100644
--- a/tests/Images/External/ReferenceOutput/DitherTests/DitherFilter_WorksWithAllDitherers_Bike_Bayer8x8.png
+++ b/tests/Images/External/ReferenceOutput/DitherTests/DitherFilter_WorksWithAllDitherers_Bike_Bayer8x8.png
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:05a0c206e13e5ad41410b1ac86720784f13594491b70b15967f761ad1feeb56e
-size 44360
+oid sha256:8af98bfcc5edef3f3ff33ee8f76f33ce2906a6677167e2b29e1dbe63b00a78d8
+size 44202
diff --git a/tests/Images/External/ReferenceOutput/DitherTests/DitherFilter_WorksWithAllDitherers_Bike_Ordered3x3.png b/tests/Images/External/ReferenceOutput/DitherTests/DitherFilter_WorksWithAllDitherers_Bike_Ordered3x3.png
index a09c2faec8..d67f02dca5 100644
--- a/tests/Images/External/ReferenceOutput/DitherTests/DitherFilter_WorksWithAllDitherers_Bike_Ordered3x3.png
+++ b/tests/Images/External/ReferenceOutput/DitherTests/DitherFilter_WorksWithAllDitherers_Bike_Ordered3x3.png
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:87069e28d286edc6edd6b53af8c3c8bc81bdbd6a16e67487c3ea45170fc29805
-size 45060
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