Optimize effor diffusion. Fix #757

src/ImageSharp/Advanced/AotCompilerTools.cs

@@ -136,7 +136,7 @@ namespace SixLabors.ImageSharp.Advanced
             TPixel pixel = default;
             using (var image = new ImageFrame<TPixel>(Configuration.Default, 1, 1))
             {
-                test.Dither(image, pixel, pixel, 0, 0, 0, 0, 0, 0);
+                test.Dither(image, pixel, pixel, 0, 0, 0, 0, 0);
             }
         }
 

src/ImageSharp/Processing/Extensions/DiffuseExtensions.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors and contributors.
+// Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
 using System;
@@ -95,4 +95,4 @@ namespace SixLabors.ImageSharp.Processing.Dithering
             Rectangle rectangle) =>
             source.ApplyProcessor(new ErrorDiffusionPaletteProcessor(diffuser, threshold, palette), rectangle);
     }
-}
+}

src/ImageSharp/Processing/Processors/Binarization/BinaryErrorDiffusionProcessor{TPixel}.cs

@@ -14,7 +14,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Binarization
     /// Performs binary threshold filtering against an image using error diffusion.
     /// </summary>
     /// <typeparam name="TPixel">The pixel format.</typeparam>
-    internal class BinaryErrorDiffusionProcessor<TPixel> : ImageProcessor<TPixel>
+    internal sealed class BinaryErrorDiffusionProcessor<TPixel> : ImageProcessor<TPixel>
         where TPixel : struct, IPixel<TPixel>
     {
         private readonly BinaryErrorDiffusionProcessor definition;
@@ -76,7 +76,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Binarization
                     }
 
                     TPixel transformedPixel = luminance >= threshold ? upperColor : lowerColor;
-                    diffuser.Dither(source, sourcePixel, transformedPixel, x, y, startX, startY, endX, endY);
+                    diffuser.Dither(source, sourcePixel, transformedPixel, x, y, startX, endX, endY);
                 }
             }
         }

src/ImageSharp/Processing/Processors/Dithering/AtkinsonDiffuser.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors and contributors.
+// Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
 using SixLabors.ImageSharp.Primitives;
@@ -11,22 +11,24 @@ namespace SixLabors.ImageSharp.Processing.Processors.Dithering
     /// </summary>
     public sealed class AtkinsonDiffuser : ErrorDiffuser
     {
+        private const float Divisor = 8F;
+
         /// <summary>
         /// The diffusion matrix
         /// </summary>
         private static readonly DenseMatrix<float> AtkinsonMatrix =
             new float[,]
             {
-               { 0, 0, 1, 1 },
-               { 1, 1, 1, 0 },
-               { 0, 1, 0, 0 }
+               { 0, 0, 1 / Divisor, 1 / Divisor },
+               { 1 / Divisor, 1 / Divisor, 1 / Divisor, 0 },
+               { 0, 1 / Divisor, 0, 0 }
             };
 
         /// <summary>
         /// Initializes a new instance of the <see cref="AtkinsonDiffuser"/> class.
         /// </summary>
         public AtkinsonDiffuser()
-            : base(AtkinsonMatrix, 8)
+            : base(AtkinsonMatrix)
         {
         }
     }

src/ImageSharp/Processing/Processors/Dithering/BurksDiffuser.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors and contributors.
+// Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
 using SixLabors.ImageSharp.Primitives;
@@ -11,22 +11,24 @@ namespace SixLabors.ImageSharp.Processing.Processors.Dithering
     /// </summary>
     public sealed class BurksDiffuser : ErrorDiffuser
     {
+        private const float Divisor = 32F;
+
         /// <summary>
         /// The diffusion matrix
         /// </summary>
         private static readonly DenseMatrix<float> BurksMatrix =
             new float[,]
             {
-                { 0, 0, 0, 8, 4 },
-                { 2, 4, 8, 4, 2 }
+                { 0, 0, 0, 8 / Divisor, 4 / Divisor },
+                { 2 / Divisor, 4 / Divisor, 8 / Divisor, 4 / Divisor, 2 / Divisor }
             };
 
         /// <summary>
         /// Initializes a new instance of the <see cref="BurksDiffuser"/> class.
         /// </summary>
         public BurksDiffuser()
-            : base(BurksMatrix, 32)
+            : base(BurksMatrix)
         {
         }
     }
-}
+}

src/ImageSharp/Processing/Processors/Dithering/ErrorDiffuser.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors and contributors.
+// Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
 using System;
@@ -15,61 +15,32 @@ namespace SixLabors.ImageSharp.Processing.Processors.Dithering
     /// </summary>
     public abstract class ErrorDiffuser : IErrorDiffuser
     {
-        /// <summary>
-        /// The vector to perform division.
-        /// </summary>
-        private readonly Vector4 divisorVector;
-
-        /// <summary>
-        /// The matrix width.
-        /// </summary>
-        private readonly int matrixHeight;
-
-        /// <summary>
-        /// The matrix height.
-        /// </summary>
-        private readonly int matrixWidth;
-
-        /// <summary>
-        /// The offset at which to start the dithering operation.
-        /// </summary>
         private readonly int startingOffset;
-
-        /// <summary>
-        /// The diffusion matrix.
-        /// </summary>
         private readonly DenseMatrix<float> matrix;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="ErrorDiffuser"/> class.
         /// </summary>
         /// <param name="matrix">The dithering matrix.</param>
-        /// <param name="divisor">The divisor.</param>
-        internal ErrorDiffuser(in DenseMatrix<float> matrix, byte divisor)
+        internal ErrorDiffuser(in DenseMatrix<float> matrix)
         {
-            Guard.MustBeGreaterThan(divisor, 0, nameof(divisor));
-
-            this.matrix = matrix;
-            this.matrixWidth = this.matrix.Columns;
-            this.matrixHeight = this.matrix.Rows;
-            this.divisorVector = new Vector4(divisor);
-
             this.startingOffset = 0;
-            for (int i = 0; i < this.matrixWidth; i++)
+
+            for (int col = 0; col < matrix.Columns; col++)
             {
-                // Good to disable here as we are not comparing mathematical output.
-                // ReSharper disable once CompareOfFloatsByEqualityOperator
-                if (matrix[0, i] != 0)
+                if (matrix[0, col] != 0)
                 {
-                    this.startingOffset = (byte)(i - 1);
+                    this.startingOffset = col - 1;
                     break;
                 }
             }
+
+            this.matrix = matrix;
         }
 
         /// <inheritdoc />
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public void Dither<TPixel>(ImageFrame<TPixel> image, TPixel source, TPixel transformed, int x, int y, int minX, int minY, int maxX, int maxY)
+        [MethodImpl(InliningOptions.ShortMethod)]
+        public void Dither<TPixel>(ImageFrame<TPixel> image, TPixel source, TPixel transformed, int x, int y, int minX, int maxX, int maxY)
             where TPixel : struct, IPixel<TPixel>
         {
             image[x, y] = transformed;
@@ -82,45 +53,40 @@ namespace SixLabors.ImageSharp.Processing.Processors.Dithering
 
             // Calculate the error
             Vector4 error = source.ToVector4() - transformed.ToVector4();
-            this.DoDither(image, x, y, minX, minY, maxX, maxY, error);
+            this.DoDither(image, x, y, minX, maxX, maxY, error);
         }
 
-        [MethodImpl(MethodImplOptions.NoInlining)]
-        private void DoDither<TPixel>(ImageFrame<TPixel> image, int x, int y, int minX, int minY, int maxX, int maxY, Vector4 error)
+        [MethodImpl(InliningOptions.ShortMethod)]
+        private void DoDither<TPixel>(ImageFrame<TPixel> image, int x, int y, int minX, int maxX, int maxY, Vector4 error)
             where TPixel : struct, IPixel<TPixel>
         {
+            int offset = this.startingOffset;
+            DenseMatrix<float> matrix = this.matrix;
+
             // Loop through and distribute the error amongst neighboring pixels.
-            for (int row = 0; row < this.matrixHeight; row++)
+            for (int row = 0, targetY = y + row; row < matrix.Rows && targetY < maxY; row++)
             {
-                int matrixY = y + row;
-                if (matrixY > minY && matrixY < maxY)
-                {
-                    Span<TPixel> rowSpan = image.GetPixelRowSpan(matrixY);
+                Span<TPixel> rowSpan = image.GetPixelRowSpan(targetY);
 
-                    for (int col = 0; col < this.matrixWidth; col++)
+                for (int col = 0; col < matrix.Columns; col++)
+                {
+                    int targetX = x + (col - offset);
+                    if (targetX > minX && targetX < maxX)
                     {
-                        int matrixX = x + (col - this.startingOffset);
-
-                        if (matrixX > minX && matrixX < maxX)
+                        float coefficient = matrix[row, col];
+                        if (coefficient == 0)
                         {
-                            float coefficient = this.matrix[row, col];
-
-                            // Good to disable here as we are not comparing mathematical output.
-                            // ReSharper disable once CompareOfFloatsByEqualityOperator
-                            if (coefficient == 0)
-                            {
-                                continue;
-                            }
+                            continue;
+                        }
 
-                            ref TPixel pixel = ref rowSpan[matrixX];
-                            var offsetColor = pixel.ToVector4();
+                        ref TPixel pixel = ref rowSpan[targetX];
+                        var offsetColor = pixel.ToVector4();
 
-                            Vector4 result = ((error * coefficient) / this.divisorVector) + offsetColor;
-                            pixel.FromVector4(result);
-                        }
+                        Vector4 result = (error * coefficient) + offsetColor;
+                        pixel.FromVector4(result);
                     }
                 }
             }
         }
     }
-}
+}

src/ImageSharp/Processing/Processors/Dithering/ErrorDiffusionPaletteProcessor{TPixel}.cs

@@ -13,7 +13,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Dithering
     /// An <see cref="IImageProcessor{TPixel}"/> that dithers an image using error diffusion.
     /// </summary>
     /// <typeparam name="TPixel">The pixel format.</typeparam>
-    internal class ErrorDiffusionPaletteProcessor<TPixel> : PaletteDitherProcessor<TPixel>
+    internal sealed class ErrorDiffusionPaletteProcessor<TPixel> : PaletteDitherProcessor<TPixel>
         where TPixel : struct, IPixel<TPixel>
     {
         /// <summary>
@@ -79,7 +79,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Dithering
                     }
 
                     TPixel transformedPixel = luminance >= threshold ? pair.Second : pair.First;
-                    this.Definition.Diffuser.Dither(source, sourcePixel, transformedPixel, x, y, startX, startY, endX, endY);
+                    this.Definition.Diffuser.Dither(source, sourcePixel, transformedPixel, x, y, startX, endX, endY);
                 }
             }
         }

src/ImageSharp/Processing/Processors/Dithering/FloydSteinbergDiffuser.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors and contributors.
+// Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
 using SixLabors.ImageSharp.Primitives;
@@ -11,22 +11,24 @@ namespace SixLabors.ImageSharp.Processing.Processors.Dithering
     /// </summary>
     public sealed class FloydSteinbergDiffuser : ErrorDiffuser
     {
+        private const float Divisor = 16F;
+
         /// <summary>
         /// The diffusion matrix
         /// </summary>
         private static readonly DenseMatrix<float> FloydSteinbergMatrix =
             new float[,]
             {
-                { 0, 0, 7 },
-                { 3, 5, 1 }
+                { 0, 0, 7 / Divisor },
+                { 3 / Divisor, 5 / Divisor, 1 / Divisor }
             };
 
         /// <summary>
         /// Initializes a new instance of the <see cref="FloydSteinbergDiffuser"/> class.
         /// </summary>
         public FloydSteinbergDiffuser()
-            : base(FloydSteinbergMatrix, 16)
+            : base(FloydSteinbergMatrix)
         {
         }
     }
-}
+}

src/ImageSharp/Processing/Processors/Dithering/IErrorDiffuser.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors and contributors.
+// Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
 using SixLabors.ImageSharp.PixelFormats;
@@ -19,11 +19,10 @@ namespace SixLabors.ImageSharp.Processing.Processors.Dithering
         /// <param name="x">The column index.</param>
         /// <param name="y">The row index.</param>
         /// <param name="minX">The minimum column value.</param>
-        /// <param name="minY">The minimum row value.</param>
         /// <param name="maxX">The maximum column value.</param>
         /// <param name="maxY">The maximum row value.</param>
         /// <typeparam name="TPixel">The pixel format.</typeparam>
-        void Dither<TPixel>(ImageFrame<TPixel> image, TPixel source, TPixel transformed, int x, int y, int minX, int minY, int maxX, int maxY)
+        void Dither<TPixel>(ImageFrame<TPixel> image, TPixel source, TPixel transformed, int x, int y, int minX, int maxX, int maxY)
             where TPixel : struct, IPixel<TPixel>;
     }
-}
+}

src/ImageSharp/Processing/Processors/Dithering/JarvisJudiceNinkeDiffuser.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors and contributors.
+// Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
 using SixLabors.ImageSharp.Primitives;
@@ -11,23 +11,25 @@ namespace SixLabors.ImageSharp.Processing.Processors.Dithering
     /// </summary>
     public sealed class JarvisJudiceNinkeDiffuser : ErrorDiffuser
     {
+        private const float Divisor = 48F;
+
         /// <summary>
         /// The diffusion matrix
         /// </summary>
         private static readonly DenseMatrix<float> JarvisJudiceNinkeMatrix =
             new float[,]
             {
-                { 0, 0, 0, 7, 5 },
-                { 3, 5, 7, 5, 3 },
-                { 1, 3, 5, 3, 1 }
+                { 0, 0, 0, 7 / Divisor, 5 / Divisor },
+                { 3 / Divisor, 5 / Divisor, 7 / Divisor, 5 / Divisor, 3 / Divisor },
+                { 1 / Divisor, 3 / Divisor, 5 / Divisor, 3 / Divisor, 1 / Divisor }
             };
 
         /// <summary>
         /// Initializes a new instance of the <see cref="JarvisJudiceNinkeDiffuser"/> class.
         /// </summary>
         public JarvisJudiceNinkeDiffuser()
-            : base(JarvisJudiceNinkeMatrix, 48)
+            : base(JarvisJudiceNinkeMatrix)
         {
         }
     }
-}
+}

src/ImageSharp/Processing/Processors/Dithering/Sierra2Diffuser.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors and contributors.
+// Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
 using SixLabors.ImageSharp.Primitives;
@@ -11,22 +11,24 @@ namespace SixLabors.ImageSharp.Processing.Processors.Dithering
     /// </summary>
     public sealed class Sierra2Diffuser : ErrorDiffuser
     {
+        private const float Divisor = 16F;
+
         /// <summary>
         /// The diffusion matrix
         /// </summary>
         private static readonly DenseMatrix<float> Sierra2Matrix =
             new float[,]
             {
-               { 0, 0, 0, 4, 3 },
-               { 1, 2, 3, 2, 1 }
+               { 0, 0, 0, 4 / Divisor, 3 / Divisor },
+               { 1 / Divisor, 2 / Divisor, 3 / Divisor, 2 / Divisor, 1 / Divisor }
             };
 
         /// <summary>
         /// Initializes a new instance of the <see cref="Sierra2Diffuser"/> class.
         /// </summary>
         public Sierra2Diffuser()
-            : base(Sierra2Matrix, 16)
+            : base(Sierra2Matrix)
         {
         }
     }
-}
+}

src/ImageSharp/Processing/Processors/Dithering/Sierra3Diffuser.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors and contributors.
+// Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
 using SixLabors.ImageSharp.Primitives;
@@ -11,23 +11,25 @@ namespace SixLabors.ImageSharp.Processing.Processors.Dithering
     /// </summary>
     public sealed class Sierra3Diffuser : ErrorDiffuser
     {
+        private const float Divisor = 32F;
+
         /// <summary>
         /// The diffusion matrix
         /// </summary>
         private static readonly DenseMatrix<float> Sierra3Matrix =
             new float[,]
             {
-               { 0, 0, 0, 5, 3 },
-               { 2, 4, 5, 4, 2 },
-               { 0, 2, 3, 2, 0 }
+               { 0, 0, 0, 5 / Divisor, 3 / Divisor },
+               { 2 / Divisor, 4 / Divisor, 5 / Divisor, 4 / Divisor, 2 / Divisor },
+               { 0, 2 / Divisor, 3 / Divisor, 2 / Divisor, 0 }
             };
 
         /// <summary>
         /// Initializes a new instance of the <see cref="Sierra3Diffuser"/> class.
         /// </summary>
         public Sierra3Diffuser()
-            : base(Sierra3Matrix, 32)
+            : base(Sierra3Matrix)
         {
         }
     }
-}
+}

src/ImageSharp/Processing/Processors/Dithering/SierraLiteDiffuser.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors and contributors.
+// Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
 using SixLabors.ImageSharp.Primitives;
@@ -11,22 +11,24 @@ namespace SixLabors.ImageSharp.Processing.Processors.Dithering
     /// </summary>
     public sealed class SierraLiteDiffuser : ErrorDiffuser
     {
+        private const float Divisor = 4F;
+
         /// <summary>
         /// The diffusion matrix
         /// </summary>
         private static readonly DenseMatrix<float> SierraLiteMatrix =
             new float[,]
             {
-               { 0, 0, 2 },
-               { 1, 1, 0 }
+               { 0, 0, 2 / Divisor },
+               { 1 / Divisor, 1 / Divisor, 0 }
             };
 
         /// <summary>
         /// Initializes a new instance of the <see cref="SierraLiteDiffuser"/> class.
         /// </summary>
         public SierraLiteDiffuser()
-            : base(SierraLiteMatrix, 4)
+            : base(SierraLiteMatrix)
         {
         }
     }
-}
+}

src/ImageSharp/Processing/Processors/Dithering/StevensonArceDiffuser.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors and contributors.
+// Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
 using SixLabors.ImageSharp.Primitives;
@@ -10,24 +10,26 @@ namespace SixLabors.ImageSharp.Processing.Processors.Dithering
     /// </summary>
     public sealed class StevensonArceDiffuser : ErrorDiffuser
     {
+        private const float Divisor = 200F;
+
         /// <summary>
         /// The diffusion matrix
         /// </summary>
         private static readonly DenseMatrix<float> StevensonArceMatrix =
             new float[,]
             {
-               { 0,  0,  0,  0,  0, 32,  0 },
-               { 12, 0, 26,  0, 30,  0, 16 },
-               { 0, 12,  0, 26,  0, 12,  0 },
-               { 5,  0, 12,  0, 12,  0,  5 }
+               { 0,  0,  0,  0,  0, 32 / Divisor,  0 },
+               { 12 / Divisor, 0, 26 / Divisor,  0, 30 / Divisor,  0, 16 / Divisor },
+               { 0, 12 / Divisor,  0, 26 / Divisor,  0, 12 / Divisor,  0 },
+               { 5 / Divisor,  0, 12 / Divisor,  0, 12 / Divisor,  0,  5 / Divisor }
             };
 
         /// <summary>
         /// Initializes a new instance of the <see cref="StevensonArceDiffuser"/> class.
         /// </summary>
         public StevensonArceDiffuser()
-            : base(StevensonArceMatrix, 200)
+            : base(StevensonArceMatrix)
         {
         }
     }
-}
+}

src/ImageSharp/Processing/Processors/Dithering/StuckiDiffuser.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors and contributors.
+// Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
 using SixLabors.ImageSharp.Primitives;
@@ -11,23 +11,25 @@ namespace SixLabors.ImageSharp.Processing.Processors.Dithering
     /// </summary>
     public sealed class StuckiDiffuser : ErrorDiffuser
     {
+        private const float Divisor = 42F;
+
         /// <summary>
         /// The diffusion matrix
         /// </summary>
         private static readonly DenseMatrix<float> StuckiMatrix =
             new float[,]
             {
-               { 0, 0, 0, 8, 4 },
-               { 2, 4, 8, 4, 2 },
-               { 1, 2, 4, 2, 1 }
+               { 0, 0, 0, 8 / Divisor, 4 / Divisor },
+               { 2 / Divisor, 4 / Divisor, 8 / Divisor, 4 / Divisor, 2 / Divisor },
+               { 1 / Divisor, 2 / Divisor, 4 / Divisor, 2 / Divisor, 1 / Divisor }
             };
 
         /// <summary>
         /// Initializes a new instance of the <see cref="StuckiDiffuser"/> class.
         /// </summary>
         public StuckiDiffuser()
-            : base(StuckiMatrix, 42)
+            : base(StuckiMatrix)
         {
         }
     }
-}
+}

src/ImageSharp/Processing/Processors/Dithering/error_diffusion.txt

@@ -1,3 +1,6 @@
+Reference:
+http://bisqwit.iki.fi/jutut/kuvat/ordered_dither/error_diffusion.txt
+
 List of error diffusion schemes.
 
 Quantization error of *current* pixel is added to the pixels

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

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors and contributors.
+// Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
 using System;
@@ -128,7 +128,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
                     if (this.Dither)
                     {
                         // Apply the dithering matrix. We have to reapply the value now as the original has changed.
-                        this.Diffuser.Dither(source, sourcePixel, transformedPixel, x, y, 0, 0, width, height);
+                        this.Diffuser.Dither(source, sourcePixel, transformedPixel, x, y, 0, width, height);
                     }
 
                     output[(y * source.Width) + x] = pixelValue;
@@ -571,4 +571,4 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
             }
         }
     }
-}
+}

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

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors and contributors.
+// Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
 using System;
@@ -76,7 +76,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
                     if (this.Dither)
                     {
                         // Apply the dithering matrix. We have to reapply the value now as the original has changed.
-                        this.Diffuser.Dither(source, sourcePixel, transformedPixel, x, y, 0, 0, width, height);
+                        this.Diffuser.Dither(source, sourcePixel, transformedPixel, x, y, 0, width, height);
                     }
 
                     output[(y * source.Width) + x] = pixelValue;
@@ -98,4 +98,4 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         private byte QuantizePixel(ref TPixel pixel) => this.GetClosestPixel(ref pixel);
     }
-}
+}

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

@@ -260,7 +260,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
                     if (this.Dither)
                     {
                         // Apply the dithering matrix. We have to reapply the value now as the original has changed.
-                        this.Diffuser.Dither(source, sourcePixel, transformedPixel, x, y, 0, 0, width, height);
+                        this.Diffuser.Dither(source, sourcePixel, transformedPixel, x, y, 0, width, height);
                     }
 
                     output[(y * source.Width) + x] = pixelValue;

tests/ImageSharp.Benchmarks/Samplers/Diffuse.cs

@@ -0,0 +1,49 @@
+using BenchmarkDotNet.Attributes;
+using SixLabors.ImageSharp.PixelFormats;
+using SixLabors.ImageSharp.Processing;
+using SixLabors.ImageSharp.Processing.Dithering;
+using SixLabors.Primitives;
+
+namespace SixLabors.ImageSharp.Benchmarks.Samplers
+{
+    [Config(typeof(Config.ShortClr))]
+    public class Diffuse
+    {
+        [Benchmark]
+        public Size DoDiffuse()
+        {
+            using (var image = new Image<Rgba32>(Configuration.Default, 800, 800, Rgba32.BlanchedAlmond))
+            {
+                image.Mutate(x => x.Diffuse());
+
+                return image.Size();
+            }
+        }
+    }
+}
+
+// #### 25th October 2019 ####
+//
+// BenchmarkDotNet=v0.11.5, OS=Windows 10.0.18362
+// Intel Core i7-8650U CPU 1.90GHz(Kaby Lake R), 1 CPU, 8 logical and 4 physical cores
+// .NET Core SDK = 3.0.100
+// 
+//  [Host] : .NET Core 2.1.13 (CoreCLR 4.6.28008.01, CoreFX 4.6.28008.01), 64bit RyuJIT
+//   Clr    : .NET Framework 4.7.2 (CLR 4.0.30319.42000), 64bit RyuJIT-v4.8.4018.0
+//   Core   : .NET Core 2.1.13 (CoreCLR 4.6.28008.01, CoreFX 4.6.28008.01), 64bit RyuJIT
+// 
+// IterationCount=3  LaunchCount=1  WarmupCount=3
+//
+// #### Before ####
+//
+// |    Method |  Job | Runtime |      Mean |    Error |   StdDev | Gen 0 | Gen 1 | Gen 2 | Allocated |
+// |---------- |----- |-------- |----------:|---------:|---------:|------:|------:|------:|----------:|
+// | DoDiffuse |  Clr |     Clr | 129.58 ms | 24.60 ms | 1.349 ms |     - |     - |     - |      6 KB |
+// | DoDiffuse | Core |    Core |  92.63 ms | 89.78 ms | 4.921 ms |     - |     - |     - |   4.58 KB |
+// 
+// #### After ####
+// 
+// |    Method |  Job | Runtime |     Mean |    Error |   StdDev | Gen 0 | Gen 1 | Gen 2 | Allocated |
+// |---------- |----- |-------- |---------:|---------:|---------:|------:|------:|------:|----------:|
+// | DoDiffuse |  Clr |     Clr | 12.94 ms | 22.48 ms | 1.232 ms |     - |     - |     - |   4.25 KB |
+// | DoDiffuse | Core |    Core | 10.95 ms | 19.31 ms | 1.058 ms |     - |     - |     - |   4.13 KB |