Add bounded quantization and update namings.

src/ImageSharp/Processing/Extensions/Dithering/DitherExtensions.cs

@@ -18,7 +18,7 @@ namespace SixLabors.ImageSharp.Processing
         /// <param name="source">The image this method extends.</param>
         /// <returns>The <see cref="IImageProcessingContext"/> to allow chaining of operations.</returns>
         public static IImageProcessingContext Dither(this IImageProcessingContext source) =>
-            Dither(source, KnownDitherers.BayerDither4x4);
+            Dither(source, KnownDitherings.BayerDither4x4);
 
         /// <summary>
         /// Dithers the image reducing it to a web-safe palette using ordered dithering.

src/ImageSharp/Processing/Extensions/Quantization/QuantizeExtensions.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.Processing.Processors.Quantization;
@@ -27,5 +27,28 @@ namespace SixLabors.ImageSharp.Processing
         /// <returns>The <see cref="IImageProcessingContext"/> to allow chaining of operations.</returns>
         public static IImageProcessingContext Quantize(this IImageProcessingContext source, IQuantizer quantizer) =>
             source.ApplyProcessor(new QuantizeProcessor(quantizer));
+
+        /// <summary>
+        /// Applies quantization to the image using the <see cref="OctreeQuantizer"/>.
+        /// </summary>
+        /// <param name="source">The image this method extends.</param>
+        /// <param name="rectangle">
+        /// The <see cref="Rectangle"/> structure that specifies the portion of the image object to alter.
+        /// </param>
+        /// <returns>The <see cref="IImageProcessingContext"/> to allow chaining of operations.</returns>
+        public static IImageProcessingContext Quantize(this IImageProcessingContext source, Rectangle rectangle) =>
+            Quantize(source, KnownQuantizers.Octree, rectangle);
+
+        /// <summary>
+        /// Applies quantization to the image.
+        /// </summary>
+        /// <param name="source">The image this method extends.</param>
+        /// <param name="quantizer">The quantizer to apply to perform the operation.</param>
+        /// <param name="rectangle">
+        /// The <see cref="Rectangle"/> structure that specifies the portion of the image object to alter.
+        /// </param>
+        /// <returns>The <see cref="IImageProcessingContext"/> to allow chaining of operations.</returns>
+        public static IImageProcessingContext Quantize(this IImageProcessingContext source, IQuantizer quantizer, Rectangle rectangle) =>
+            source.ApplyProcessor(new QuantizeProcessor(quantizer), rectangle);
     }
-}
+}

src/ImageSharp/Processing/KnownDitherers.cs → src/ImageSharp/Processing/KnownDitherings.cs

@@ -6,9 +6,9 @@ using SixLabors.ImageSharp.Processing.Processors.Dithering;
 namespace SixLabors.ImageSharp.Processing
 {
     /// <summary>
-    /// Contains reusable static instances of known ordered dither matrices
+    /// Contains reusable static instances of known dithering algorithms.
     /// </summary>
-    public static class KnownDitherers
+    public static class KnownDitherings
     {
         /// <summary>
         /// Gets the order ditherer using the 2x2 Bayer dithering matrix

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

@@ -182,16 +182,17 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
             if (this.Dither.DitherType == DitherType.ErrorDiffusion)
             {
                 int width = bounds.Width;
+                int offsetY = bounds.Top;
                 int offsetX = bounds.Left;
                 for (int y = bounds.Top; y < bounds.Bottom; y++)
                 {
                     Span<TPixel> row = source.GetPixelRowSpan(y);
-                    int offset = y * width;
+                    int rowStart = (y - offsetY) * width;
 
                     for (int x = bounds.Left; x < bounds.Right; x++)
                     {
                         TPixel sourcePixel = row[x];
-                        outputSpan[offset + x - offsetX] = this.GetQuantizedColor(sourcePixel, paletteSpan, out TPixel transformed);
+                        outputSpan[rowStart + x - offsetX] = this.GetQuantizedColor(sourcePixel, paletteSpan, out TPixel transformed);
                         this.Dither.Dither(source, bounds, sourcePixel, transformed, x, y, bitDepth);
                     }
                 }
@@ -255,16 +256,17 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
                 ReadOnlySpan<TPixel> paletteSpan = this.palette.Span;
                 Span<byte> outputSpan = this.output.Span;
                 int width = this.bounds.Width;
+                int offsetY = this.bounds.Top;
                 int offsetX = this.bounds.Left;
 
                 for (int y = rows.Min; y < rows.Max; y++)
                 {
                     Span<TPixel> row = this.source.GetPixelRowSpan(y);
-                    int offset = y * width;
+                    int rowStart = (y - offsetY) * width;
 
                     for (int x = this.bounds.Left; x < this.bounds.Right; x++)
                     {
-                        outputSpan[offset + x - offsetX] = this.quantizer.GetQuantizedColor(row[x], paletteSpan, out TPixel _);
+                        outputSpan[rowStart + x - offsetX] = this.quantizer.GetQuantizedColor(row[x], paletteSpan, out TPixel _);
                     }
                 }
             }
@@ -302,18 +304,20 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
                 ReadOnlySpan<TPixel> paletteSpan = this.palette.Span;
                 Span<byte> outputSpan = this.output.Span;
                 int width = this.bounds.Width;
+                int offsetY = this.bounds.Top;
+                int offsetX = this.bounds.Left;
                 IDither dither = this.quantizer.Dither;
                 TPixel transformed = default;
-                int offsetX = this.bounds.Left;
 
                 for (int y = rows.Min; y < rows.Max; y++)
                 {
                     Span<TPixel> row = this.source.GetPixelRowSpan(y);
-                    int offset = y * width;
+                    int rowStart = (y - offsetY) * width;
+
                     for (int x = this.bounds.Left; x < this.bounds.Right; x++)
                     {
                         TPixel dithered = dither.Dither(this.source, this.bounds, row[x], transformed, x, y, this.bitDepth);
-                        outputSpan[offset + x - offsetX] = this.quantizer.GetQuantizedColor(dithered, paletteSpan, out TPixel _);
+                        outputSpan[rowStart + x - offsetX] = this.quantizer.GetQuantizedColor(dithered, paletteSpan, out TPixel _);
                     }
                 }
             }

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

@@ -2,11 +2,12 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System;
+using System.Buffers;
 using System.Collections.Generic;
 using System.Numerics;
 using System.Runtime.CompilerServices;
-using System.Runtime.InteropServices;
 using SixLabors.ImageSharp.Advanced;
+using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;
 
 namespace SixLabors.ImageSharp.Processing.Processors.Quantization
@@ -68,20 +69,21 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
         /// <inheritdoc/>
         protected override void FirstPass(ImageFrame<TPixel> source, Rectangle bounds)
         {
+            using IMemoryOwner<Rgba32> buffer = this.Configuration.MemoryAllocator.Allocate<Rgba32>(bounds.Width);
+            Span<Rgba32> bufferSpan = buffer.GetSpan();
+
             // Loop through each row
-            int offset = bounds.Left;
             for (int y = bounds.Top; y < bounds.Bottom; y++)
             {
-                Span<TPixel> row = source.GetPixelRowSpan(y);
-                ref TPixel scanBaseRef = ref MemoryMarshal.GetReference(row);
+                Span<TPixel> row = source.GetPixelRowSpan(y).Slice(bounds.Left, bounds.Width);
+                PixelOperations<TPixel>.Instance.ToRgba32(this.Configuration, row, bufferSpan);
 
-                // And loop through each column
-                for (int x = bounds.Left; x < bounds.Right; x++)
+                for (int x = 0; x < bufferSpan.Length; x++)
                 {
-                    ref TPixel pixel = ref Unsafe.Add(ref scanBaseRef, x - offset);
+                    Rgba32 rgba = bufferSpan[x];
 
                     // Add the color to the Octree
-                    this.octree.AddColor(ref pixel);
+                    this.octree.AddColor(rgba);
                 }
             }
         }
@@ -92,7 +94,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
         {
             if (!this.DoDither)
             {
-                var index = (byte)this.octree.GetPaletteIndex(ref color);
+                var index = (byte)this.octree.GetPaletteIndex(color);
                 match = palette[index];
                 return index;
             }
@@ -113,10 +115,19 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
         private sealed class Octree
         {
             /// <summary>
-            /// Mask used when getting the appropriate pixels for a given node
+            /// Mask used when getting the appropriate pixels for a given node.
             /// </summary>
-            // ReSharper disable once StaticMemberInGenericType
-            private static readonly int[] Mask = { 0x80, 0x40, 0x20, 0x10, 0x08, 0x04, 0x02, 0x01 };
+            private static readonly byte[] Mask = new byte[]
+            {
+                0b10000000,
+                0b1000000,
+                0b100000,
+                0b10000,
+                0b1000,
+                0b100,
+                0b10,
+                0b1
+            };
 
             /// <summary>
             /// The root of the Octree
@@ -136,7 +147,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
             /// <summary>
             /// Cache the previous color quantized
             /// </summary>
-            private TPixel previousColor;
+            private Rgba32 previousColor;
 
             /// <summary>
             /// Initializes a new instance of the <see cref="Octree"/> class.
@@ -178,29 +189,30 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
             /// <summary>
             /// Add a given color value to the Octree
             /// </summary>
-            /// <param name="pixel">The pixel data.</param>
-            public void AddColor(ref TPixel pixel)
+            /// <param name="color">The color to add.</param>
+            public void AddColor(Rgba32 color)
             {
                 // Check if this request is for the same color as the last
-                if (this.previousColor.Equals(pixel))
+                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
+                    // 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 = pixel;
-                        this.root.AddColor(ref pixel, this.maxColorBits, 0, this);
+                        this.previousColor = color;
+                        this.root.AddColor(ref color, this.maxColorBits, 0, this);
                     }
                     else
                     {
                         // Just update the previous node
-                        this.previousNode.Increment(ref pixel);
+                        this.previousNode.Increment(ref color);
                     }
                 }
                 else
                 {
-                    this.previousColor = pixel;
-                    this.root.AddColor(ref pixel, this.maxColorBits, 0, this);
+                    this.previousColor = color;
+                    this.root.AddColor(ref color, this.maxColorBits, 0, this);
                 }
             }
 
@@ -232,12 +244,17 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
             /// <summary>
             /// Get the palette index for the passed color
             /// </summary>
-            /// <param name="pixel">The pixel data.</param>
+            /// <param name="color">The color to match.</param>
             /// <returns>
-            /// The <see cref="int"/>.
+            /// The <see cref="int"/> index.
             /// </returns>
             [MethodImpl(InliningOptions.ShortMethod)]
-            public int GetPaletteIndex(ref TPixel pixel) => this.root.GetPaletteIndex(ref pixel, 0);
+            public int GetPaletteIndex(TPixel color)
+            {
+                Rgba32 rgba = default;
+                color.ToRgba32(ref rgba);
+                return this.root.GetPaletteIndex(ref rgba, 0);
+            }
 
             /// <summary>
             /// Keep track of the previous node that was quantized
@@ -360,16 +377,16 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
                 /// <summary>
                 /// Add a color into the tree
                 /// </summary>
-                /// <param name="pixel">The pixel color</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(ref TPixel pixel, int colorBits, int level, Octree octree)
+                /// <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(ref Rgba32 color, int colorBits, int level, Octree octree)
                 {
                     // Update the color information if this is a leaf
                     if (this.leaf)
                     {
-                        this.Increment(ref pixel);
+                        this.Increment(ref color);
 
                         // Setup the previous node
                         octree.TrackPrevious(this);
@@ -377,13 +394,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
                     else
                     {
                         // Go to the next level down in the tree
-                        int shift = 7 - level;
-                        Rgba32 rgba = default;
-                        pixel.ToRgba32(ref rgba);
-
-                        int index = ((rgba.B & Mask[level]) >> (shift - 2))
-                                    | ((rgba.G & Mask[level]) >> (shift - 1))
-                                    | ((rgba.R & Mask[level]) >> shift);
+                        int index = GetColorIndex(ref color, level);
 
                         OctreeNode child = this.children[index];
                         if (child is null)
@@ -394,7 +405,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
                         }
 
                         // Add the color to the child node
-                        child.AddColor(ref pixel, colorBits, level + 1, octree);
+                        child.AddColor(ref color, colorBits, level + 1, octree);
                     }
                 }
 
@@ -467,29 +478,35 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
                 /// The <see cref="int"/> representing the index of the pixel in the palette.
                 /// </returns>
                 [MethodImpl(InliningOptions.ColdPath)]
-                public int GetPaletteIndex(ref TPixel pixel, int level)
+                public int GetPaletteIndex(ref Rgba32 pixel, int level)
                 {
-                    int index = this.paletteIndex;
-
-                    if (!this.leaf)
+                    if (this.leaf)
                     {
-                        int shift = 7 - level;
-                        Rgba32 rgba = default;
-                        pixel.ToRgba32(ref rgba);
+                        return this.paletteIndex;
+                    }
 
-                        int pixelIndex = ((rgba.B & Mask[level]) >> (shift - 2))
-                                         | ((rgba.G & Mask[level]) >> (shift - 1))
-                                         | ((rgba.R & Mask[level]) >> shift);
+                    int colorIndex = GetColorIndex(ref pixel, level);
+                    OctreeNode child = this.children[colorIndex];
 
-                        OctreeNode child = this.children[pixelIndex];
-                        if (child != null)
-                        {
-                            index = child.GetPaletteIndex(ref pixel, level + 1);
-                        }
-                        else
+                    int index = 0;
+                    if (child != null)
+                    {
+                        index = child.GetPaletteIndex(ref pixel, level + 1);
+                    }
+                    else
+                    {
+                        // Check other children.
+                        for (int i = 0; i < this.children.Length; i++)
                         {
-                            // TODO: Throw helper.
-                            throw new Exception($"Cannot retrieve a pixel at the given index {pixelIndex}.");
+                            child = this.children[i];
+                            if (child != null)
+                            {
+                                var childIndex = child.GetPaletteIndex(ref pixel, level + 1);
+                                if (childIndex != 0)
+                                {
+                                    return childIndex;
+                                }
+                            }
                         }
                     }
 
@@ -497,18 +514,32 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
                 }
 
                 /// <summary>
-                /// Increment the pixel count and add to the color information
+                /// 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(ref Rgba32 color, int level)
+                {
+                    int shift = 7 - level;
+                    byte mask = Mask[level];
+                    return ((color.B & mask) >> (shift - 2))
+                         | ((color.G & mask) >> (shift - 1))
+                         | ((color.R & mask) >> shift);
+                }
+
+                /// <summary>
+                /// Increment the color count and add to the color information
                 /// </summary>
-                /// <param name="pixel">The pixel to add.</param>
+                /// <param name="color">The pixel to add.</param>
                 [MethodImpl(InliningOptions.ShortMethod)]
-                public void Increment(ref TPixel pixel)
+                public void Increment(ref Rgba32 color)
                 {
-                    Rgba32 rgba = default;
-                    pixel.ToRgba32(ref rgba);
                     this.pixelCount++;
-                    this.red += rgba.R;
-                    this.green += rgba.G;
-                    this.blue += rgba.B;
+                    this.red += color.R;
+                    this.green += color.G;
+                    this.blue += color.B;
                 }
             }
         }

src/ImageSharp/Processing/Processors/Quantization/OctreeQuantizer.cs

@@ -10,7 +10,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
     /// Allows the quantization of images pixels using Octrees.
     /// <see href="http://msdn.microsoft.com/en-us/library/aa479306.aspx"/>
     /// <para>
-    /// By default the quantizer uses <see cref="KnownDitherers.FloydSteinberg"/> dithering and a color palette of a maximum length of <value>255</value>
+    /// By default the quantizer uses <see cref="KnownDitherings.FloydSteinberg"/> dithering and a color palette of a maximum length of <value>255</value>
     /// </para>
     /// </summary>
     public class OctreeQuantizer : IQuantizer
@@ -93,6 +93,6 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
             return new OctreeFrameQuantizer<TPixel>(configuration, this, maxColors);
         }
 
-        private static IDither GetDiffuser(bool dither) => dither ? KnownDitherers.FloydSteinberg : null;
+        private static IDither GetDiffuser(bool dither) => dither ? KnownDitherings.FloydSteinberg : null;
     }
 }

src/ImageSharp/Processing/Processors/Quantization/PaletteQuantizer.cs

@@ -12,7 +12,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
     /// Allows the quantization of images pixels using color palettes.
     /// Override this class to provide your own palette.
     /// <para>
-    /// By default the quantizer uses <see cref="KnownDitherers.FloydSteinberg"/> dithering.
+    /// By default the quantizer uses <see cref="KnownDitherings.FloydSteinberg"/> dithering.
     /// </para>
     /// </summary>
     public class PaletteQuantizer : IQuantizer
@@ -76,6 +76,6 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
             return new PaletteFrameQuantizer<TPixel>(configuration, this.Dither, palette);
         }
 
-        private static IDither GetDiffuser(bool dither) => dither ? KnownDitherers.FloydSteinberg : null;
+        private static IDither GetDiffuser(bool dither) => dither ? KnownDitherings.FloydSteinberg : null;
     }
 }

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

@@ -53,7 +53,6 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
             private readonly Rectangle bounds;
             private readonly ImageFrame<TPixel> source;
             private readonly IQuantizedFrame<TPixel> quantized;
-            private readonly int maxPaletteIndex;
 
             [MethodImpl(InliningOptions.ShortMethod)]
             public RowIntervalOperation(
@@ -64,7 +63,6 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
                 this.bounds = bounds;
                 this.source = source;
                 this.quantized = quantized;
-                this.maxPaletteIndex = quantized.Palette.Length - 1;
             }
 
             [MethodImpl(InliningOptions.ShortMethod)]
@@ -72,17 +70,19 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
             {
                 ReadOnlySpan<byte> quantizedPixelSpan = this.quantized.GetPixelSpan();
                 ReadOnlySpan<TPixel> paletteSpan = this.quantized.Palette.Span;
+                int offsetY = this.bounds.Top;
+                int offsetX = this.bounds.Left;
+                int width = this.bounds.Width;
 
-                int offset = this.bounds.Left;
                 for (int y = rows.Min; y < rows.Max; y++)
                 {
                     Span<TPixel> row = this.source.GetPixelRowSpan(y);
-                    int yy = y * this.bounds.Width;
+                    int rowStart = (y - offsetY) * width;
 
                     for (int x = this.bounds.Left; x < this.bounds.Right; x++)
                     {
-                        int i = yy + x - offset;
-                        row[x] = paletteSpan[Math.Min(this.maxPaletteIndex, quantizedPixelSpan[i])];
+                        int i = rowStart + x - offsetX;
+                        row[x] = paletteSpan[quantizedPixelSpan[i]];
                     }
                 }
             }

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

@@ -384,29 +384,24 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
             Span<Moment> momentSpan = this.moments.GetSpan();
 
             // Build up the 3-D color histogram
-            // Loop through each row
-            using IMemoryOwner<Rgba32> rgbaBuffer = this.memoryAllocator.Allocate<Rgba32>(source.Width);
-            Span<Rgba32> rgbaSpan = rgbaBuffer.GetSpan();
-            ref Rgba32 scanBaseRef = ref MemoryMarshal.GetReference(rgbaSpan);
+            using IMemoryOwner<Rgba32> buffer = this.memoryAllocator.Allocate<Rgba32>(bounds.Width);
+            Span<Rgba32> bufferSpan = buffer.GetSpan();
 
-            int offset = bounds.Left;
             for (int y = bounds.Top; y < bounds.Bottom; y++)
             {
-                Span<TPixel> row = source.GetPixelRowSpan(y);
-                PixelOperations<TPixel>.Instance.ToRgba32(source.GetConfiguration(), row, rgbaSpan);
+                Span<TPixel> row = source.GetPixelRowSpan(y).Slice(bounds.Left, bounds.Width);
+                PixelOperations<TPixel>.Instance.ToRgba32(this.Configuration, row, bufferSpan);
 
-                // And loop through each column
-                for (int x = bounds.Left; x < bounds.Right; x++)
+                for (int x = 0; x < bufferSpan.Length; x++)
                 {
-                    ref Rgba32 rgba = ref Unsafe.Add(ref scanBaseRef, x - offset);
+                    Rgba32 rgba = bufferSpan[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;
 
-                    int index = GetPaletteIndex(r, g, b, a);
-                    momentSpan[index] += rgba;
+                    momentSpan[GetPaletteIndex(r, g, b, a)] += rgba;
                 }
             }
         }

src/ImageSharp/Processing/Processors/Quantization/WuQuantizer.cs

@@ -9,7 +9,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
     /// <summary>
     /// Allows the quantization of images pixels using Xiaolin Wu's Color Quantizer <see href="http://www.ece.mcmaster.ca/~xwu/cq.c"/>
     /// <para>
-    /// By default the quantizer uses <see cref="KnownDitherers.FloydSteinberg"/> dithering and a color palette of a maximum length of <value>255</value>
+    /// By default the quantizer uses <see cref="KnownDitherings.FloydSteinberg"/> dithering and a color palette of a maximum length of <value>255</value>
     /// </para>
     /// </summary>
     public class WuQuantizer : IQuantizer
@@ -85,6 +85,6 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
             return new WuFrameQuantizer<TPixel>(configuration, this, maxColors);
         }
 
-        private static IDither GetDiffuser(bool dither) => dither ? KnownDitherers.FloydSteinberg : null;
+        private static IDither GetDiffuser(bool dither) => dither ? KnownDitherings.FloydSteinberg : null;
     }
 }

tests/ImageSharp.Benchmarks/Samplers/Diffuse.cs

@@ -15,7 +15,7 @@ namespace SixLabors.ImageSharp.Benchmarks.Samplers
         {
             using (var image = new Image<Rgba32>(Configuration.Default, 800, 800, Color.BlanchedAlmond))
             {
-                image.Mutate(x => x.Dither(KnownDitherers.FloydSteinberg));
+                image.Mutate(x => x.Dither(KnownDitherings.FloydSteinberg));
 
                 return image.Size();
             }

tests/ImageSharp.Tests/Processing/Dithering/DitherTest.cs

@@ -29,8 +29,8 @@ namespace SixLabors.ImageSharp.Tests.Processing.Binarization
 
         public DitherTest()
         {
-            this.orderedDither = KnownDitherers.BayerDither4x4;
-            this.errorDiffuser = KnownDitherers.FloydSteinberg;
+            this.orderedDither = KnownDitherings.BayerDither4x4;
+            this.errorDiffuser = KnownDitherings.FloydSteinberg;
         }
 
         [Fact]

tests/ImageSharp.Tests/Processing/Processors/Binarization/BinaryDitherTests.cs

@@ -20,30 +20,30 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Binarization
 
         public static readonly TheoryData<string, IDither> OrderedDitherers = new TheoryData<string, IDither>
         {
-            { "Bayer8x8", KnownDitherers.BayerDither8x8 },
-            { "Bayer4x4", KnownDitherers.BayerDither4x4 },
-            { "Ordered3x3", KnownDitherers.OrderedDither3x3 },
-            { "Bayer2x2", KnownDitherers.BayerDither2x2 }
+            { "Bayer8x8", KnownDitherings.BayerDither8x8 },
+            { "Bayer4x4", KnownDitherings.BayerDither4x4 },
+            { "Ordered3x3", KnownDitherings.OrderedDither3x3 },
+            { "Bayer2x2", KnownDitherings.BayerDither2x2 }
         };
 
         public static readonly TheoryData<string, IDither> ErrorDiffusers = new TheoryData<string, IDither>
         {
-            { "Atkinson", KnownDitherers.Atkinson },
-            { "Burks", KnownDitherers.Burks },
-            { "FloydSteinberg", KnownDitherers.FloydSteinberg },
-            { "JarvisJudiceNinke", KnownDitherers.JarvisJudiceNinke },
-            { "Sierra2", KnownDitherers.Sierra2 },
-            { "Sierra3", KnownDitherers.Sierra3 },
-            { "SierraLite", KnownDitherers.SierraLite },
-            { "StevensonArce", KnownDitherers.StevensonArce },
-            { "Stucki", KnownDitherers.Stucki },
+            { "Atkinson", KnownDitherings.Atkinson },
+            { "Burks", KnownDitherings.Burks },
+            { "FloydSteinberg", KnownDitherings.FloydSteinberg },
+            { "JarvisJudiceNinke", KnownDitherings.JarvisJudiceNinke },
+            { "Sierra2", KnownDitherings.Sierra2 },
+            { "Sierra3", KnownDitherings.Sierra3 },
+            { "SierraLite", KnownDitherings.SierraLite },
+            { "StevensonArce", KnownDitherings.StevensonArce },
+            { "Stucki", KnownDitherings.Stucki },
         };
 
         public const PixelTypes TestPixelTypes = PixelTypes.Rgba32 | PixelTypes.Bgra32 | PixelTypes.Rgb24;
 
-        private static IDither DefaultDitherer => KnownDitherers.BayerDither4x4;
+        private static IDither DefaultDitherer => KnownDitherings.BayerDither4x4;
 
-        private static IDither DefaultErrorDiffuser => KnownDitherers.Atkinson;
+        private static IDither DefaultErrorDiffuser => KnownDitherings.Atkinson;
 
         [Theory]
         [WithFileCollection(nameof(CommonTestImages), nameof(OrderedDitherers), PixelTypes.Rgba32)]

tests/ImageSharp.Tests/Processing/Processors/Dithering/DitherTests.cs

@@ -20,31 +20,31 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Binarization
         public static readonly TheoryData<IDither> ErrorDiffusers
             = new TheoryData<IDither>
             {
-                KnownDitherers.Atkinson,
-                KnownDitherers.Burks,
-                KnownDitherers.FloydSteinberg,
-                KnownDitherers.JarvisJudiceNinke,
-                KnownDitherers.Sierra2,
-                KnownDitherers.Sierra3,
-                KnownDitherers.SierraLite,
-                KnownDitherers.StevensonArce,
-                KnownDitherers.Stucki,
+                KnownDitherings.Atkinson,
+                KnownDitherings.Burks,
+                KnownDitherings.FloydSteinberg,
+                KnownDitherings.JarvisJudiceNinke,
+                KnownDitherings.Sierra2,
+                KnownDitherings.Sierra3,
+                KnownDitherings.SierraLite,
+                KnownDitherings.StevensonArce,
+                KnownDitherings.Stucki,
             };
 
         public static readonly TheoryData<IDither> OrderedDitherers
             = new TheoryData<IDither>
             {
-                KnownDitherers.BayerDither8x8,
-                KnownDitherers.BayerDither4x4,
-                KnownDitherers.OrderedDither3x3,
-                KnownDitherers.BayerDither2x2
+                KnownDitherings.BayerDither8x8,
+                KnownDitherings.BayerDither4x4,
+                KnownDitherings.OrderedDither3x3,
+                KnownDitherings.BayerDither2x2
             };
 
         private static readonly ImageComparer ValidatorComparer = ImageComparer.TolerantPercentage(0.05f);
 
-        private static IDither DefaultDitherer => KnownDitherers.BayerDither4x4;
+        private static IDither DefaultDitherer => KnownDitherings.BayerDither4x4;
 
-        private static IDither DefaultErrorDiffuser => KnownDitherers.Atkinson;
+        private static IDither DefaultErrorDiffuser => KnownDitherings.Atkinson;
 
         /// <summary>
         /// The output is visually correct old 32bit runtime,

tests/ImageSharp.Tests/Processing/Processors/Quantization/OctreeQuantizerTests.cs

@@ -16,19 +16,19 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Quantization
             var quantizer = new OctreeQuantizer(128);
 
             Assert.Equal(128, quantizer.MaxColors);
-            Assert.Equal(KnownDitherers.FloydSteinberg, quantizer.Dither);
+            Assert.Equal(KnownDitherings.FloydSteinberg, quantizer.Dither);
 
             quantizer = new OctreeQuantizer(false);
             Assert.Equal(QuantizerConstants.MaxColors, quantizer.MaxColors);
             Assert.Null(quantizer.Dither);
 
-            quantizer = new OctreeQuantizer(KnownDitherers.Atkinson);
+            quantizer = new OctreeQuantizer(KnownDitherings.Atkinson);
             Assert.Equal(QuantizerConstants.MaxColors, quantizer.MaxColors);
-            Assert.Equal(KnownDitherers.Atkinson, quantizer.Dither);
+            Assert.Equal(KnownDitherings.Atkinson, quantizer.Dither);
 
-            quantizer = new OctreeQuantizer(KnownDitherers.Atkinson, 128);
+            quantizer = new OctreeQuantizer(KnownDitherings.Atkinson, 128);
             Assert.Equal(128, quantizer.MaxColors);
-            Assert.Equal(KnownDitherers.Atkinson, quantizer.Dither);
+            Assert.Equal(KnownDitherings.Atkinson, quantizer.Dither);
         }
 
         [Fact]
@@ -39,7 +39,8 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Quantization
 
             Assert.NotNull(frameQuantizer);
             Assert.True(frameQuantizer.DoDither);
-            Assert.Equal(KnownDitherers.FloydSteinberg, frameQuantizer.Dither);
+            Assert.Equal(KnownDitherings.FloydSteinberg, frameQuantizer.Dither);
+            frameQuantizer.Dispose();
 
             quantizer = new OctreeQuantizer(false);
             frameQuantizer = quantizer.CreateFrameQuantizer<Rgba32>(Configuration.Default);
@@ -47,12 +48,14 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Quantization
             Assert.NotNull(frameQuantizer);
             Assert.False(frameQuantizer.DoDither);
             Assert.Null(frameQuantizer.Dither);
+            frameQuantizer.Dispose();
 
-            quantizer = new OctreeQuantizer(KnownDitherers.Atkinson);
+            quantizer = new OctreeQuantizer(KnownDitherings.Atkinson);
             frameQuantizer = quantizer.CreateFrameQuantizer<Rgba32>(Configuration.Default);
             Assert.NotNull(frameQuantizer);
             Assert.True(frameQuantizer.DoDither);
-            Assert.Equal(KnownDitherers.Atkinson, frameQuantizer.Dither);
+            Assert.Equal(KnownDitherings.Atkinson, frameQuantizer.Dither);
+            frameQuantizer.Dispose();
         }
     }
 }

tests/ImageSharp.Tests/Processing/Processors/Quantization/PaletteQuantizerTests.cs

@@ -18,15 +18,15 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Quantization
             var quantizer = new PaletteQuantizer(Rgb);
 
             Assert.Equal(Rgb, quantizer.Palette);
-            Assert.Equal(KnownDitherers.FloydSteinberg, quantizer.Dither);
+            Assert.Equal(KnownDitherings.FloydSteinberg, quantizer.Dither);
 
             quantizer = new PaletteQuantizer(Rgb, false);
             Assert.Equal(Rgb, quantizer.Palette);
             Assert.Null(quantizer.Dither);
 
-            quantizer = new PaletteQuantizer(Rgb, KnownDitherers.Atkinson);
+            quantizer = new PaletteQuantizer(Rgb, KnownDitherings.Atkinson);
             Assert.Equal(Rgb, quantizer.Palette);
-            Assert.Equal(KnownDitherers.Atkinson, quantizer.Dither);
+            Assert.Equal(KnownDitherings.Atkinson, quantizer.Dither);
         }
 
         [Fact]
@@ -37,7 +37,8 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Quantization
 
             Assert.NotNull(frameQuantizer);
             Assert.True(frameQuantizer.DoDither);
-            Assert.Equal(KnownDitherers.FloydSteinberg, frameQuantizer.Dither);
+            Assert.Equal(KnownDitherings.FloydSteinberg, frameQuantizer.Dither);
+            frameQuantizer.Dispose();
 
             quantizer = new PaletteQuantizer(Rgb, false);
             frameQuantizer = quantizer.CreateFrameQuantizer<Rgba32>(Configuration.Default);
@@ -45,26 +46,28 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Quantization
             Assert.NotNull(frameQuantizer);
             Assert.False(frameQuantizer.DoDither);
             Assert.Null(frameQuantizer.Dither);
+            frameQuantizer.Dispose();
 
-            quantizer = new PaletteQuantizer(Rgb, KnownDitherers.Atkinson);
+            quantizer = new PaletteQuantizer(Rgb, KnownDitherings.Atkinson);
             frameQuantizer = quantizer.CreateFrameQuantizer<Rgba32>(Configuration.Default);
             Assert.NotNull(frameQuantizer);
             Assert.True(frameQuantizer.DoDither);
-            Assert.Equal(KnownDitherers.Atkinson, frameQuantizer.Dither);
+            Assert.Equal(KnownDitherings.Atkinson, frameQuantizer.Dither);
+            frameQuantizer.Dispose();
         }
 
         [Fact]
         public void KnownQuantizersWebSafeTests()
         {
             IQuantizer quantizer = KnownQuantizers.WebSafe;
-            Assert.Equal(KnownDitherers.FloydSteinberg, quantizer.Dither);
+            Assert.Equal(KnownDitherings.FloydSteinberg, quantizer.Dither);
         }
 
         [Fact]
         public void KnownQuantizersWernerTests()
         {
             IQuantizer quantizer = KnownQuantizers.Werner;
-            Assert.Equal(KnownDitherers.FloydSteinberg, quantizer.Dither);
+            Assert.Equal(KnownDitherings.FloydSteinberg, quantizer.Dither);
         }
     }
 }

tests/ImageSharp.Tests/Processing/Processors/Quantization/QuantizerTests.cs

@@ -0,0 +1,73 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+using SixLabors.ImageSharp.PixelFormats;
+using SixLabors.ImageSharp.Processing;
+using SixLabors.ImageSharp.Processing.Processors.Quantization;
+using SixLabors.ImageSharp.Tests.TestUtilities.ImageComparison;
+using Xunit;
+
+namespace SixLabors.ImageSharp.Tests.Processing.Processors.Quantization
+{
+    public class QuantizerTests
+    {
+        public static readonly string[] CommonTestImages =
+        {
+            TestImages.Png.CalliphoraPartial,
+            TestImages.Png.Bike
+        };
+
+        public static readonly TheoryData<IQuantizer> Quantizers
+        = new TheoryData<IQuantizer>
+        {
+            KnownQuantizers.Octree,
+            KnownQuantizers.WebSafe,
+            KnownQuantizers.Werner,
+            KnownQuantizers.Wu,
+            new OctreeQuantizer(false),
+            new WebSafePaletteQuantizer(false),
+            new WernerPaletteQuantizer(false),
+            new WuQuantizer(false),
+            new OctreeQuantizer(KnownDitherings.BayerDither8x8),
+            new WebSafePaletteQuantizer(KnownDitherings.BayerDither8x8),
+            new WernerPaletteQuantizer(KnownDitherings.BayerDither8x8),
+            new WuQuantizer(KnownDitherings.BayerDither8x8)
+        };
+
+        private static readonly ImageComparer ValidatorComparer = ImageComparer.TolerantPercentage(0.05f);
+
+        [Theory]
+        [WithFileCollection(nameof(CommonTestImages), nameof(Quantizers), PixelTypes.Rgba32)]
+        public void ApplyQuantizationInBox<TPixel>(TestImageProvider<TPixel> provider, IQuantizer quantizer)
+            where TPixel : struct, IPixel<TPixel>
+        {
+            string quantizerName = quantizer.GetType().Name;
+            string ditherName = quantizer.Dither?.GetType()?.Name ?? "noDither";
+            string ditherType = quantizer.Dither?.DitherType.ToString() ?? string.Empty;
+            string testOutputDetails = $"{quantizerName}_{ditherName}_{ditherType}";
+
+            provider.RunRectangleConstrainedValidatingProcessorTest(
+                (x, rect) => x.Quantize(quantizer, rect),
+                comparer: ValidatorComparer,
+                testOutputDetails: testOutputDetails,
+                appendPixelTypeToFileName: false);
+        }
+
+        [Theory]
+        [WithFileCollection(nameof(CommonTestImages), nameof(Quantizers), PixelTypes.Rgba32)]
+        public void ApplyQuantization<TPixel>(TestImageProvider<TPixel> provider, IQuantizer quantizer)
+            where TPixel : struct, IPixel<TPixel>
+        {
+            string quantizerName = quantizer.GetType().Name;
+            string ditherName = quantizer.Dither?.GetType()?.Name ?? "noDither";
+            string ditherType = quantizer.Dither?.DitherType.ToString() ?? string.Empty;
+            string testOutputDetails = $"{quantizerName}_{ditherName}_{ditherType}";
+
+            provider.RunValidatingProcessorTest(
+                x => x.Quantize(quantizer),
+                comparer: ValidatorComparer,
+                testOutputDetails: testOutputDetails,
+                appendPixelTypeToFileName: false);
+        }
+    }
+}

tests/ImageSharp.Tests/Processing/Processors/Quantization/WuQuantizerTests.cs

@@ -16,19 +16,19 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Quantization
             var quantizer = new WuQuantizer(128);
 
             Assert.Equal(128, quantizer.MaxColors);
-            Assert.Equal(KnownDitherers.FloydSteinberg, quantizer.Dither);
+            Assert.Equal(KnownDitherings.FloydSteinberg, quantizer.Dither);
 
             quantizer = new WuQuantizer(false);
             Assert.Equal(QuantizerConstants.MaxColors, quantizer.MaxColors);
             Assert.Null(quantizer.Dither);
 
-            quantizer = new WuQuantizer(KnownDitherers.Atkinson);
+            quantizer = new WuQuantizer(KnownDitherings.Atkinson);
             Assert.Equal(QuantizerConstants.MaxColors, quantizer.MaxColors);
-            Assert.Equal(KnownDitherers.Atkinson, quantizer.Dither);
+            Assert.Equal(KnownDitherings.Atkinson, quantizer.Dither);
 
-            quantizer = new WuQuantizer(KnownDitherers.Atkinson, 128);
+            quantizer = new WuQuantizer(KnownDitherings.Atkinson, 128);
             Assert.Equal(128, quantizer.MaxColors);
-            Assert.Equal(KnownDitherers.Atkinson, quantizer.Dither);
+            Assert.Equal(KnownDitherings.Atkinson, quantizer.Dither);
         }
 
         [Fact]
@@ -39,7 +39,8 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Quantization
 
             Assert.NotNull(frameQuantizer);
             Assert.True(frameQuantizer.DoDither);
-            Assert.Equal(KnownDitherers.FloydSteinberg, frameQuantizer.Dither);
+            Assert.Equal(KnownDitherings.FloydSteinberg, frameQuantizer.Dither);
+            frameQuantizer.Dispose();
 
             quantizer = new WuQuantizer(false);
             frameQuantizer = quantizer.CreateFrameQuantizer<Rgba32>(Configuration.Default);
@@ -47,12 +48,14 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Quantization
             Assert.NotNull(frameQuantizer);
             Assert.False(frameQuantizer.DoDither);
             Assert.Null(frameQuantizer.Dither);
+            frameQuantizer.Dispose();
 
-            quantizer = new WuQuantizer(KnownDitherers.Atkinson);
+            quantizer = new WuQuantizer(KnownDitherings.Atkinson);
             frameQuantizer = quantizer.CreateFrameQuantizer<Rgba32>(Configuration.Default);
             Assert.NotNull(frameQuantizer);
             Assert.True(frameQuantizer.DoDither);
-            Assert.Equal(KnownDitherers.Atkinson, frameQuantizer.Dither);
+            Assert.Equal(KnownDitherings.Atkinson, frameQuantizer.Dither);
+            frameQuantizer.Dispose();
         }
     }
 }

tests/ImageSharp.Tests/TestUtilities/TestImageExtensions.cs

@@ -342,10 +342,10 @@ namespace SixLabors.ImageSharp.Tests
 
             if (!File.Exists(referenceOutputFile))
             {
-                throw new System.IO.FileNotFoundException("Reference output file missing: " + referenceOutputFile, referenceOutputFile);
+                throw new FileNotFoundException("Reference output file missing: " + referenceOutputFile, referenceOutputFile);
             }
 
-            decoder = decoder ?? TestEnvironment.GetReferenceDecoder(referenceOutputFile);
+            decoder ??= TestEnvironment.GetReferenceDecoder(referenceOutputFile);
 
             return Image.Load<TPixel>(referenceOutputFile, decoder);
         }

tests/ImageSharp.Tests/TestUtilities/TestUtils.cs

@@ -294,7 +294,8 @@ namespace SixLabors.ImageSharp.Tests
             this TestImageProvider<TPixel> provider,
             Action<IImageProcessingContext, Rectangle> process,
             object testOutputDetails = null,
-            ImageComparer comparer = null)
+            ImageComparer comparer = null,
+            bool appendPixelTypeToFileName = true)
             where TPixel : struct, IPixel<TPixel>
         {
             if (comparer == null)
@@ -307,7 +308,7 @@ namespace SixLabors.ImageSharp.Tests
                 var bounds = new Rectangle(image.Width / 4, image.Width / 4, image.Width / 2, image.Height / 2);
                 image.Mutate(x => process(x, bounds));
                 image.DebugSave(provider, testOutputDetails);
-                image.CompareToReferenceOutput(comparer, provider, testOutputDetails);
+                image.CompareToReferenceOutput(comparer, provider, testOutputDetails, appendPixelTypeToFileName: appendPixelTypeToFileName);
             }
         }