Fix build, simplify utilities

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>
 
   <!--

src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs

@@ -368,7 +368,7 @@ internal sealed class BmpEncoderCore
             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;

src/ImageSharp/Formats/EncodingUtilities.cs

@@ -27,71 +27,58 @@ internal static class EncodingUtilities
         => 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 @@ internal static class EncodingUtilities
 
                 // 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 @@ internal static class EncodingUtilities
                 {
                     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 @@ internal static class EncodingUtilities
 
                 // 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 @@ internal static class EncodingUtilities
                 {
                     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 @@ internal static class EncodingUtilities
 
                 // 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 @@ internal static class EncodingUtilities
             {
                 if (source[i].W == 0F)
                 {
-                    source[i] = replacement;
+                    source[i] = Vector4.Zero;
                 }
             }
         }

src/ImageSharp/Formats/Gif/GifEncoderCore.cs

@@ -146,12 +146,16 @@ internal sealed class GifEncoderCore
             }
         }
 
+        // 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;

src/ImageSharp/Formats/Png/PngDecoderCore.cs

@@ -1086,7 +1086,7 @@ internal sealed class PngDecoderCore : ImageDecoderCore
             {
                 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 @@ internal sealed class PngDecoderCore : ImageDecoderCore
             {
                 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

src/ImageSharp/Formats/Png/PngEncoderCore.cs

@@ -197,7 +197,7 @@ internal sealed class PngEncoderCore : IDisposable
             {
                 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 @@ internal sealed class PngEncoderCore : IDisposable
 
                     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.

src/ImageSharp/Formats/Qoi/QoiEncoderCore.cs

@@ -90,10 +90,12 @@ internal class QoiEncoderCore
         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;

src/ImageSharp/Formats/Tga/TgaEncoderCore.cs

@@ -110,10 +110,12 @@ internal sealed class TgaEncoderCore
         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;

src/ImageSharp/Formats/Tiff/TiffEncoderCore.cs

@@ -146,10 +146,12 @@ internal sealed class TiffEncoderCore
             {
                 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;

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
 {

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();
 }

src/ImageSharp/Processing/Processors/Quantization/OctreeQuantizer{TPixel}.cs

@@ -45,7 +45,7 @@ public struct OctreeQuantizer<TPixel> : IQuantizer<TPixel>
 
         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 @@ public struct OctreeQuantizer<TPixel> : IQuantizer<TPixel>
         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 @@ public struct OctreeQuantizer<TPixel> : IQuantizer<TPixel>
         /// <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 struct OctreeQuantizer<TPixel> : IQuantizer<TPixel>
 
                     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 struct OctreeQuantizer<TPixel> : IQuantizer<TPixel>
             /// <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;

src/ImageSharp/Processing/Processors/Quantization/PaletteQuantizer{TPixel}.cs

@@ -98,6 +98,7 @@ internal struct PaletteQuantizer<TPixel> : IQuantizer<TPixel>
     [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;

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 class QuantizerOptions
         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 class QuantizerOptions
     }
 
     /// <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);
 }

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 class QuantizerUtilities
         => 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 class QuantizerUtilities
 
                 // 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 class QuantizerUtilities
                 {
                     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 class QuantizerUtilities
 
                 // 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 class QuantizerUtilities
                 {
                     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 class QuantizerUtilities
 
                 // 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 class QuantizerUtilities
             {
                 if (source[i].W < threshold)
                 {
-                    source[i] = replacement;
+                    source[i] = Vector4.Zero;
                 }
             }
         }
@@ -336,7 +334,7 @@ public static class QuantizerUtilities
     {
         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 @@ public static class QuantizerUtilities
         {
             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 @@ public static class QuantizerUtilities
                     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 @@ public static class QuantizerUtilities
                     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 @@ public static class QuantizerUtilities
         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 @@ public static class QuantizerUtilities
                         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 @@ public static class QuantizerUtilities
                         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 @@ public static class QuantizerUtilities
                     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 @@ public static class QuantizerUtilities
                     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);
                 }

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 @@ internal struct WuQuantizer<TPixel> : IQuantizer<TPixel>
         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 @@ internal struct WuQuantizer<TPixel> : IQuantizer<TPixel>
         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 @@ internal struct WuQuantizer<TPixel> : IQuantizer<TPixel>
                 Vector4 normalized = moment.Normalize();
                 if (normalized.W < transparencyThreshold)
                 {
-                    normalized = thresholdReplacementColor;
+                    normalized = Vector4.Zero;
                 }
 
                 paletteSpan[k] = TPixel.FromScaledVector4(normalized);
@@ -188,10 +181,6 @@ internal struct WuQuantizer<TPixel> : IQuantizer<TPixel>
         }
 
         Rgba32 rgba = color.ToRgba32();
-        if (rgba.A < this.transparencyThreshold255)
-        {
-            rgba = this.thresholdReplacementColorRgba;
-        }
 
         const int shift = 8 - IndexBits;
         int r = rgba.R >> shift;