Cleanup and fix tests.

src/ImageSharp/Advanced/AotCompilerTools.cs

@@ -124,7 +124,8 @@ namespace SixLabors.ImageSharp.Advanced
         {
             using (var test = new WuFrameQuantizer<TPixel>(Configuration.Default, new WuQuantizer(false)))
             {
-                test.QuantizeFrame(new ImageFrame<TPixel>(Configuration.Default, 1, 1));
+                var frame = new ImageFrame<TPixel>(Configuration.Default, 1, 1);
+                test.QuantizeFrame(frame, frame.Bounds());
                 test.AotGetPalette();
             }
         }

src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs

@@ -335,36 +335,36 @@ namespace SixLabors.ImageSharp.Formats.Bmp
         private void Write8BitColor<TPixel>(Stream stream, ImageFrame<TPixel> image, Span<byte> colorPalette)
             where TPixel : struct, IPixel<TPixel>
         {
-            using (IQuantizedFrame<TPixel> quantized = this.quantizer.CreateFrameQuantizer<TPixel>(this.configuration, 256).QuantizeFrame(image))
+            using IFrameQuantizer<TPixel> quantizer = this.quantizer.CreateFrameQuantizer<TPixel>(this.configuration, 256);
+            using IQuantizedFrame<TPixel> quantized = quantizer.QuantizeFrame(image, image.Bounds());
+
+            ReadOnlySpan<TPixel> quantizedColors = quantized.Palette.Span;
+            var color = default(Rgba32);
+
+            // TODO: Use bulk conversion here for better perf
+            int idx = 0;
+            foreach (TPixel quantizedColor in quantizedColors)
             {
-                ReadOnlySpan<TPixel> quantizedColors = quantized.Palette.Span;
-                var color = default(Rgba32);
+                quantizedColor.ToRgba32(ref color);
+                colorPalette[idx] = color.B;
+                colorPalette[idx + 1] = color.G;
+                colorPalette[idx + 2] = color.R;
 
-                // TODO: Use bulk conversion here for better perf
-                int idx = 0;
-                foreach (TPixel quantizedColor in quantizedColors)
-                {
-                    quantizedColor.ToRgba32(ref color);
-                    colorPalette[idx] = color.B;
-                    colorPalette[idx + 1] = color.G;
-                    colorPalette[idx + 2] = color.R;
-
-                    // Padding byte, always 0.
-                    colorPalette[idx + 3] = 0;
-                    idx += 4;
-                }
+                // Padding byte, always 0.
+                colorPalette[idx + 3] = 0;
+                idx += 4;
+            }
+
+            stream.Write(colorPalette);
 
-                stream.Write(colorPalette);
+            for (int y = image.Height - 1; y >= 0; y--)
+            {
+                ReadOnlySpan<byte> pixelSpan = quantized.GetRowSpan(y);
+                stream.Write(pixelSpan);
 
-                for (int y = image.Height - 1; y >= 0; y--)
+                for (int i = 0; i < this.padding; i++)
                 {
-                    ReadOnlySpan<byte> pixelSpan = quantized.GetRowSpan(y);
-                    stream.Write(pixelSpan);
-
-                    for (int i = 0; i < this.padding; i++)
-                    {
-                        stream.WriteByte(0);
-                    }
+                    stream.WriteByte(0);
                 }
             }
         }

src/ImageSharp/Formats/Gif/GifEncoderCore.cs

@@ -28,7 +28,7 @@ namespace SixLabors.ImageSharp.Formats.Gif
         /// <summary>
         /// Configuration bound to the encoding operation.
         /// </summary>
-        private Configuration configuration;
+        private readonly Configuration configuration;
 
         /// <summary>
         /// A reusable buffer used to reduce allocations.
@@ -84,7 +84,7 @@ namespace SixLabors.ImageSharp.Formats.Gif
             IQuantizedFrame<TPixel> quantized;
             using (IFrameQuantizer<TPixel> frameQuantizer = this.quantizer.CreateFrameQuantizer<TPixel>(this.configuration))
             {
-                quantized = frameQuantizer.QuantizeFrame(image.Frames.RootFrame);
+                quantized = frameQuantizer.QuantizeFrame(image.Frames.RootFrame, image.Bounds());
             }
 
             // Get the number of bits.
@@ -147,7 +147,7 @@ namespace SixLabors.ImageSharp.Formats.Gif
                     using (IFrameQuantizer<TPixel> paletteFrameQuantizer =
                         new PaletteFrameQuantizer<TPixel>(this.configuration, this.quantizer.Dither, quantized.Palette))
                     {
-                        using (IQuantizedFrame<TPixel> paletteQuantized = paletteFrameQuantizer.QuantizeFrame(frame))
+                        using (IQuantizedFrame<TPixel> paletteQuantized = paletteFrameQuantizer.QuantizeFrame(frame, frame.Bounds()))
                         {
                             this.WriteImageData(paletteQuantized, stream);
                         }
@@ -173,14 +173,14 @@ namespace SixLabors.ImageSharp.Formats.Gif
                     {
                         using (IFrameQuantizer<TPixel> frameQuantizer = this.quantizer.CreateFrameQuantizer<TPixel>(this.configuration, frameMetadata.ColorTableLength))
                         {
-                            quantized = frameQuantizer.QuantizeFrame(frame);
+                            quantized = frameQuantizer.QuantizeFrame(frame, frame.Bounds());
                         }
                     }
                     else
                     {
                         using (IFrameQuantizer<TPixel> frameQuantizer = this.quantizer.CreateFrameQuantizer<TPixel>(this.configuration))
                         {
-                            quantized = frameQuantizer.QuantizeFrame(frame);
+                            quantized = frameQuantizer.QuantizeFrame(frame, frame.Bounds());
                         }
                     }
                 }

src/ImageSharp/Formats/Png/PngEncoderOptionsHelpers.cs

@@ -78,7 +78,8 @@ namespace SixLabors.ImageSharp.Formats.Png
             // Create quantized frame returning the palette and set the bit depth.
             using (IFrameQuantizer<TPixel> frameQuantizer = options.Quantizer.CreateFrameQuantizer<TPixel>(image.GetConfiguration()))
             {
-                return frameQuantizer.QuantizeFrame(image.Frames.RootFrame);
+                ImageFrame<TPixel> frame = image.Frames.RootFrame;
+                return frameQuantizer.QuantizeFrame(frame, frame.Bounds());
             }
         }
 

src/ImageSharp/Processing/Processors/Dithering/DitherTransformColorBehavior.cs → src/ImageSharp/Processing/Processors/Dithering/DitherType.cs

@@ -6,16 +6,16 @@ namespace SixLabors.ImageSharp.Processing.Processors.Dithering
     /// <summary>
     /// Enumerates the possible dithering algorithm transform behaviors.
     /// </summary>
-    public enum DitherTransformColorBehavior
+    public enum DitherType
     {
         /// <summary>
-        /// The transformed color should be precalulated and passed to the dithering algorithm.
+        /// Error diffusion. Spreads the difference between source and quanized color values as distributed error.
         /// </summary>
-        PreOperation,
+        ErrorDiffusion,
 
         /// <summary>
-        /// The transformed color should be calculated as a result of the dithering algorithm.
+        /// Ordered dithering. Applies thresholding matrices agains the source to determine the quantized color.
         /// </summary>
-        PostOperation
+        OrderedDither
     }
 }

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

@@ -28,7 +28,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Dithering
         }
 
         /// <inheritdoc/>
-        public DitherTransformColorBehavior TransformColorBehavior { get; } = DitherTransformColorBehavior.PreOperation;
+        public DitherType DitherType { get; } = DitherType.ErrorDiffusion;
 
         /// <inheritdoc/>
         public TPixel Dither<TPixel>(

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

@@ -11,14 +11,14 @@ namespace SixLabors.ImageSharp.Processing.Processors.Dithering
     public interface IDither
     {
         /// <summary>
-        /// Gets the <see cref="DitherTransformColorBehavior"/> which determines whether the
+        /// Gets the <see cref="Dithering.DitherType"/> which determines whether the
         /// transformed color should be calculated and supplied to the algorithm.
         /// </summary>
-        public DitherTransformColorBehavior TransformColorBehavior { get; }
+        public DitherType DitherType { get; }
 
         /// <summary>
         /// Transforms the image applying a dither matrix.
-        /// When <see cref="TransformColorBehavior"/> is <see cref="DitherTransformColorBehavior.PreOperation"/> this
+        /// When <see cref="DitherType"/> is <see cref="DitherType.ErrorDiffusion"/> this
         /// this method is destructive and will alter the input pixels.
         /// </summary>
         /// <param name="image">The image.</param>

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

@@ -31,7 +31,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Dithering
             float m2 = length * length;
             for (int y = 0; y < length; y++)
             {
-                for (int x = 0; x < length; y++)
+                for (int x = 0; x < length; x++)
                 {
                     thresholdMatrix[y, x] = ((ditherMatrix[y, x] + 1) / m2) - .5F;
                 }
@@ -43,7 +43,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Dithering
         }
 
         /// <inheritdoc/>
-        public DitherTransformColorBehavior TransformColorBehavior { get; } = DitherTransformColorBehavior.PostOperation;
+        public DitherType DitherType { get; } = DitherType.OrderedDither;
 
         /// <inheritdoc/>
         [MethodImpl(InliningOptions.ShortMethod)]

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

@@ -46,7 +46,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Dithering
 
             // Error diffusion. The difference between the source and transformed color
             // is spread to neighboring pixels.
-            if (this.dither.TransformColorBehavior == DitherTransformColorBehavior.PreOperation)
+            if (this.dither.DitherType == DitherType.ErrorDiffusion)
             {
                 for (int y = interest.Top; y < interest.Bottom; y++)
                 {

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

@@ -29,14 +29,14 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
         /// Initializes a new instance of the <see cref="FrameQuantizer{TPixel}"/> class.
         /// </summary>
         /// <param name="configuration">The configuration which allows altering default behaviour or extending the library.</param>
-        /// <param name="quantizer">The quantizer</param>
+        /// <param name="quantizer">The quantizer.</param>
         /// <param name="singlePass">
-        /// If true, the quantization process only needs to loop through the source pixels once
+        /// If true, the quantization process only needs to loop through the source pixels once.
         /// </param>
         /// <remarks>
         /// If you construct this class with a <value>true</value> for <paramref name="singlePass"/>, then the code will
-        /// only call the <see cref="SecondPass(ImageFrame{TPixel}, Span{byte}, ReadOnlySpan{TPixel},  int, int)"/> method.
-        /// If two passes are required, the code will also call <see cref="FirstPass(ImageFrame{TPixel}, int, int)"/>.
+        /// only call the <see cref="SecondPass(ImageFrame{TPixel}, Rectangle, Memory{byte}, ReadOnlyMemory{TPixel})"/> method.
+        /// If two passes are required, the code will also call <see cref="FirstPass(ImageFrame{TPixel}, Rectangle)"/>.
         /// </remarks>
         protected FrameQuantizer(Configuration configuration, IQuantizer quantizer, bool singlePass)
         {
@@ -58,8 +58,8 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
         /// </param>
         /// <remarks>
         /// If you construct this class with a <value>true</value> for <paramref name="singlePass"/>, then the code will
-        /// only call the <see cref="SecondPass(ImageFrame{TPixel}, Span{byte}, ReadOnlySpan{TPixel},  int, int)"/> method.
-        /// If two passes are required, the code will also call <see cref="FirstPass(ImageFrame{TPixel}, int, int)"/>.
+        /// only call the <see cref="SecondPass(ImageFrame{TPixel}, Rectangle, Memory{byte}, ReadOnlyMemory{TPixel})"/> method.
+        /// If two passes are required, the code will also call <see cref="FirstPass(ImageFrame{TPixel}, Rectangle)"/>.
         /// </remarks>
         protected FrameQuantizer(Configuration configuration, IDither diffuser, bool singlePass)
         {
@@ -88,41 +88,38 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
         }
 
         /// <inheritdoc/>
-        public IQuantizedFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> image)
+        public IQuantizedFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> image, Rectangle bounds)
         {
             Guard.NotNull(image, nameof(image));
-
-            // Get the size of the source image
-            int height = image.Height;
-            int width = image.Width;
+            var interest = Rectangle.Intersect(image.Bounds(), bounds);
 
             // Call the FirstPass function if not a single pass algorithm.
             // For something like an Octree quantizer, this will run through
             // all image pixels, build a data structure, and create a palette.
             if (!this.singlePass)
             {
-                this.FirstPass(image, width, height);
+                this.FirstPass(image, interest);
             }
 
             // Collect the palette. Required before the second pass runs.
-            ReadOnlyMemory<TPixel> palette = this.GetPalette();
+            ReadOnlyMemory<TPixel> palette = this.GenerateQuantizedPalette();
             MemoryAllocator memoryAllocator = this.Configuration.MemoryAllocator;
             this.pixelMap = new EuclideanPixelMap<TPixel>(palette);
 
-            var quantizedFrame = new QuantizedFrame<TPixel>(memoryAllocator, width, height, palette);
+            var quantizedFrame = new QuantizedFrame<TPixel>(memoryAllocator, interest.Width, interest.Height, palette);
 
-            Span<byte> pixelSpan = quantizedFrame.GetWritablePixelSpan();
+            Memory<byte> output = quantizedFrame.GetWritablePixelMemory();
             if (this.DoDither)
             {
-                // We clone the image as we don't want to alter the original via dithering.
+                // We clone the image as we don't want to alter the original via error diffusion based dithering.
                 using (ImageFrame<TPixel> clone = image.Clone())
                 {
-                    this.SecondPass(clone, pixelSpan, palette.Span, width, height);
+                    this.SecondPass(clone, interest, output, palette);
                 }
             }
             else
             {
-                this.SecondPass(image, pixelSpan, palette.Span, width, height);
+                this.SecondPass(image, interest, output, palette);
             }
 
             return quantizedFrame;
@@ -146,9 +143,8 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
         /// Execute the first pass through the pixels in the image to create the palette.
         /// </summary>
         /// <param name="source">The source data.</param>
-        /// <param name="width">The width in pixels of the image.</param>
-        /// <param name="height">The height in pixels of the image.</param>
-        protected virtual void FirstPass(ImageFrame<TPixel> source, int width, int height)
+        /// <param name="bounds">The bounds within the source image to quantize.</param>
+        protected virtual void FirstPass(ImageFrame<TPixel> source, Rectangle bounds)
         {
         }
 
@@ -156,86 +152,169 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
         /// Returns the index and color from the quantized palette corresponding to the give to the given color.
         /// </summary>
         /// <param name="color">The color to match.</param>
+        /// <param name="palette">The output color palette.</param>
         /// <param name="match">The matched color.</param>
-        /// <returns>The <see cref="int"/></returns>
+        /// <returns>The <see cref="byte"/> index.</returns>
         [MethodImpl(InliningOptions.ShortMethod)]
-        protected virtual byte GetQuantizedColor(TPixel color, out TPixel match)
+        protected virtual byte GetQuantizedColor(TPixel color, ReadOnlySpan<TPixel> palette, out TPixel match)
             => this.pixelMap.GetClosestColor(color, out match);
 
         /// <summary>
-        /// Retrieve the palette for the quantized image.
+        /// Generates the palette for the quantized image.
         /// </summary>
         /// <returns>
         /// <see cref="ReadOnlyMemory{TPixel}"/>
         /// </returns>
-        protected abstract ReadOnlyMemory<TPixel> GetPalette();
+        protected abstract ReadOnlyMemory<TPixel> GenerateQuantizedPalette();
 
         /// <summary>
         /// Execute a second pass through the image to assign the pixels to a palette entry.
         /// </summary>
         /// <param name="source">The source image.</param>
+        /// <param name="bounds">The bounds within the source image to quantize.</param>
         /// <param name="output">The output pixel array.</param>
         /// <param name="palette">The output color palette.</param>
-        /// <param name="width">The width in pixels of the image.</param>
-        /// <param name="height">The height in pixels of the image.</param>
         protected virtual void SecondPass(
             ImageFrame<TPixel> source,
-            Span<byte> output,
-            ReadOnlySpan<TPixel> palette,
-            int width,
-            int height)
+            Rectangle bounds,
+            Memory<byte> output,
+            ReadOnlyMemory<TPixel> palette)
         {
-            Rectangle interest = source.Bounds();
-            int bitDepth = ImageMaths.GetBitsNeededForColorDepth(palette.Length);
-
+            ReadOnlySpan<TPixel> paletteSpan = palette.Span;
             if (!this.DoDither)
             {
-                // TODO: This can be parallel.
-                for (int y = interest.Top; y < interest.Bottom; y++)
+                var operation = new RowIntervalOperation(source, output, bounds, this, palette);
+                ParallelRowIterator.IterateRows(
+                    this.Configuration,
+                    bounds,
+                    in operation);
+
+                return;
+            }
+
+            // Error diffusion.
+            // The difference between the source and transformed color is spread to neighboring pixels.
+            // TODO: Investigate parallel strategy.
+            Span<byte> outputSpan = output.Span;
+
+            int bitDepth = ImageMaths.GetBitsNeededForColorDepth(paletteSpan.Length);
+            if (this.Dither.DitherType == DitherType.ErrorDiffusion)
+            {
+                int width = bounds.Width;
+                int offsetX = bounds.Left;
+                for (int y = bounds.Top; y < bounds.Bottom; y++)
                 {
                     Span<TPixel> row = source.GetPixelRowSpan(y);
                     int offset = y * width;
 
-                    for (int x = interest.Left; x < interest.Right; x++)
+                    for (int x = bounds.Left; x < bounds.Right; x++)
                     {
-                        output[offset + x] = this.GetQuantizedColor(row[x], out TPixel _);
+                        TPixel sourcePixel = row[x];
+                        outputSpan[offset + x - offsetX] = this.GetQuantizedColor(sourcePixel, paletteSpan, out TPixel transformed);
+                        this.Dither.Dither(source, bounds, sourcePixel, transformed, x, y, bitDepth);
                     }
                 }
 
                 return;
             }
 
-            // Error diffusion. The difference between the source and transformed color
-            // is spread to neighboring pixels.
-            if (this.Dither.TransformColorBehavior == DitherTransformColorBehavior.PreOperation)
+            // Ordered dithering. We are only operating on a single pixel so we can work in parallel.
+            var ditherOperation = new DitherRowIntervalOperation(source, output, bounds, this, palette, bitDepth);
+            ParallelRowIterator.IterateRows(
+                this.Configuration,
+                bounds,
+                in ditherOperation);
+        }
+
+        private readonly struct RowIntervalOperation : IRowIntervalOperation
+        {
+            private readonly ImageFrame<TPixel> source;
+            private readonly Memory<byte> output;
+            private readonly Rectangle bounds;
+            private readonly FrameQuantizer<TPixel> quantizer;
+            private readonly ReadOnlyMemory<TPixel> palette;
+
+            [MethodImpl(InliningOptions.ShortMethod)]
+            public RowIntervalOperation(
+                ImageFrame<TPixel> source,
+                Memory<byte> output,
+                Rectangle bounds,
+                FrameQuantizer<TPixel> quantizer,
+                ReadOnlyMemory<TPixel> palette)
+            {
+                this.source = source;
+                this.output = output;
+                this.bounds = bounds;
+                this.quantizer = quantizer;
+                this.palette = palette;
+            }
+
+            [MethodImpl(InliningOptions.ShortMethod)]
+            public void Invoke(in RowInterval rows)
             {
-                for (int y = interest.Top; y < interest.Bottom; y++)
+                ReadOnlySpan<TPixel> paletteSpan = this.palette.Span;
+                Span<byte> outputSpan = this.output.Span;
+                int width = this.bounds.Width;
+                int offsetX = this.bounds.Left;
+
+                for (int y = rows.Min; y < rows.Max; y++)
                 {
-                    Span<TPixel> row = source.GetPixelRowSpan(y);
+                    Span<TPixel> row = this.source.GetPixelRowSpan(y);
                     int offset = y * width;
 
-                    for (int x = interest.Left; x < interest.Right; x++)
+                    for (int x = this.bounds.Left; x < this.bounds.Right; x++)
                     {
-                        TPixel sourcePixel = row[x];
-                        output[offset + x] = this.GetQuantizedColor(sourcePixel, out TPixel transformed);
-                        this.Dither.Dither(source, interest, sourcePixel, transformed, x, y, bitDepth);
+                        outputSpan[offset + x - offsetX] = this.quantizer.GetQuantizedColor(row[x], paletteSpan, out TPixel _);
                     }
                 }
+            }
+        }
 
-                return;
+        private readonly struct DitherRowIntervalOperation : IRowIntervalOperation
+        {
+            private readonly ImageFrame<TPixel> source;
+            private readonly Memory<byte> output;
+            private readonly Rectangle bounds;
+            private readonly FrameQuantizer<TPixel> quantizer;
+            private readonly ReadOnlyMemory<TPixel> palette;
+            private readonly int bitDepth;
+
+            [MethodImpl(InliningOptions.ShortMethod)]
+            public DitherRowIntervalOperation(
+                ImageFrame<TPixel> source,
+                Memory<byte> output,
+                Rectangle bounds,
+                FrameQuantizer<TPixel> quantizer,
+                ReadOnlyMemory<TPixel> palette,
+                int bitDepth)
+            {
+                this.source = source;
+                this.output = output;
+                this.bounds = bounds;
+                this.quantizer = quantizer;
+                this.palette = palette;
+                this.bitDepth = bitDepth;
             }
 
-            // TODO: This can be parallel.
-            // Ordered dithering. We are only operating on a single pixel.
-            for (int y = interest.Top; y < interest.Bottom; y++)
+            [MethodImpl(InliningOptions.ShortMethod)]
+            public void Invoke(in RowInterval rows)
             {
-                Span<TPixel> row = source.GetPixelRowSpan(y);
-                int offset = y * width;
+                ReadOnlySpan<TPixel> paletteSpan = this.palette.Span;
+                Span<byte> outputSpan = this.output.Span;
+                int width = this.bounds.Width;
+                IDither dither = this.quantizer.Dither;
+                TPixel transformed = default;
+                int offsetX = this.bounds.Left;
 
-                for (int x = interest.Left; x < interest.Right; x++)
+                for (int y = rows.Min; y < rows.Max; y++)
                 {
-                    TPixel dithered = this.Dither.Dither(source, interest, row[x], default, x, y, bitDepth);
-                    output[offset + x] = this.GetQuantizedColor(dithered, out TPixel _);
+                    Span<TPixel> row = this.source.GetPixelRowSpan(y);
+                    int offset = y * 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 _);
+                    }
                 }
             }
         }

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

@@ -27,10 +27,11 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
         /// <summary>
         /// Quantize an image frame and return the resulting output pixels.
         /// </summary>
-        /// <param name="image">The image to quantize.</param>
+        /// <param name="source">The image to quantize.</param>
+        /// <param name="bounds">The bounds within the source image to quantize.</param>
         /// <returns>
-        /// A <see cref="QuantizedFrame{TPixel}"/> representing a quantized version of the image pixels.
+        /// A <see cref="QuantizedFrame{TPixel}"/> representing a quantized version of the source image pixels.
         /// </returns>
-        IQuantizedFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> image);
+        IQuantizedFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> source, Rectangle bounds);
     }
 }

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

@@ -29,6 +29,9 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
         /// </summary>
         private readonly Octree octree;
 
+        /// <summary>
+        /// The reduced image palette
+        /// </summary>
         private TPixel[] palette;
 
         /// <summary>
@@ -63,18 +66,19 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
         }
 
         /// <inheritdoc/>
-        protected override void FirstPass(ImageFrame<TPixel> source, int width, int height)
+        protected override void FirstPass(ImageFrame<TPixel> source, Rectangle bounds)
         {
             // Loop through each row
-            for (int y = 0; y < height; y++)
+            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);
 
                 // And loop through each column
-                for (int x = 0; x < width; x++)
+                for (int x = bounds.Left; x < bounds.Right; x++)
                 {
-                    ref TPixel pixel = ref Unsafe.Add(ref scanBaseRef, x);
+                    ref TPixel pixel = ref Unsafe.Add(ref scanBaseRef, x - offset);
 
                     // Add the color to the Octree
                     this.octree.AddColor(ref pixel);
@@ -84,23 +88,23 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
 
         /// <inheritdoc/>
         [MethodImpl(InliningOptions.ShortMethod)]
-        protected override byte GetQuantizedColor(TPixel color, out TPixel match)
+        protected override byte GetQuantizedColor(TPixel color, ReadOnlySpan<TPixel> palette, out TPixel match)
         {
             if (!this.DoDither)
             {
                 var index = (byte)this.octree.GetPaletteIndex(ref color);
-                match = this.GetPalette().Span[index];
+                match = palette[index];
                 return index;
             }
 
-            return base.GetQuantizedColor(color, out match);
+            return base.GetQuantizedColor(color, palette, out match);
         }
 
-        internal ReadOnlyMemory<TPixel> AotGetPalette() => this.GetPalette();
+        internal ReadOnlyMemory<TPixel> AotGetPalette() => this.GenerateQuantizedPalette();
 
         /// <inheritdoc/>
         [MethodImpl(InliningOptions.ShortMethod)]
-        protected override ReadOnlyMemory<TPixel> GetPalette()
+        protected override ReadOnlyMemory<TPixel> GenerateQuantizedPalette()
             => this.palette ?? (this.palette = this.octree.Palletize(this.colors));
 
         /// <summary>
@@ -430,7 +434,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
                 /// </summary>
                 /// <param name="palette">The palette</param>
                 /// <param name="index">The current palette index</param>
-                [MethodImpl(MethodImplOptions.NoInlining)]
+                [MethodImpl(InliningOptions.ColdPath)]
                 public void ConstructPalette(TPixel[] palette, ref int index)
                 {
                     if (this.leaf)
@@ -462,10 +466,9 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
                 /// <returns>
                 /// The <see cref="int"/> representing the index of the pixel in the palette.
                 /// </returns>
-                [MethodImpl(MethodImplOptions.NoInlining)]
+                [MethodImpl(InliningOptions.ColdPath)]
                 public int GetPaletteIndex(ref TPixel pixel, int level)
                 {
-                    // TODO: pass index around so we can do this in parallel.
                     int index = this.paletteIndex;
 
                     if (!this.leaf)

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

@@ -44,8 +44,8 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
         /// <summary>
         /// Initializes a new instance of the <see cref="OctreeQuantizer"/> class.
         /// </summary>
-        /// <param name="maxColors">The maximum number of colors to hold in the color palette.</param>
         /// <param name="dither">Whether to apply dithering to the output image.</param>
+        /// <param name="maxColors">The maximum number of colors to hold in the color palette.</param>
         public OctreeQuantizer(bool dither, int maxColors)
             : this(GetDiffuser(dither), maxColors)
         {

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

@@ -3,7 +3,6 @@
 
 using System;
 using System.Runtime.CompilerServices;
-using SixLabors.ImageSharp.Advanced;
 using SixLabors.ImageSharp.PixelFormats;
 using SixLabors.ImageSharp.Processing.Processors.Dithering;
 
@@ -32,70 +31,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
             : base(configuration, diffuser, true) => this.palette = colors;
 
         /// <inheritdoc/>
-        protected override void SecondPass(
-            ImageFrame<TPixel> source,
-            Span<byte> output,
-            ReadOnlySpan<TPixel> palette,
-            int width,
-            int height)
-        {
-            Rectangle interest = source.Bounds();
-            int bitDepth = ImageMaths.GetBitsNeededForColorDepth(palette.Length);
-
-            if (!this.DoDither)
-            {
-                // TODO: This can be parallel.
-                for (int y = interest.Top; y < interest.Bottom; y++)
-                {
-                    Span<TPixel> row = source.GetPixelRowSpan(y);
-                    int offset = y * width;
-
-                    for (int x = interest.Left; x < interest.Right; x++)
-                    {
-                        output[offset + x] = this.GetQuantizedColor(row[x], out TPixel _);
-                    }
-                }
-
-                return;
-            }
-
-            // Error diffusion. The difference between the source and transformed color
-            // is spread to neighboring pixels.
-            if (this.Dither.TransformColorBehavior == DitherTransformColorBehavior.PreOperation)
-            {
-                for (int y = interest.Top; y < interest.Bottom; y++)
-                {
-                    Span<TPixel> row = source.GetPixelRowSpan(y);
-                    int offset = y * width;
-
-                    for (int x = interest.Left; x < interest.Right; x++)
-                    {
-                        TPixel sourcePixel = row[x];
-                        output[offset + x] = this.GetQuantizedColor(sourcePixel, out TPixel transformed);
-                        this.Dither.Dither(source, interest, sourcePixel, transformed, x, y, bitDepth);
-                    }
-                }
-
-                return;
-            }
-
-            // TODO: This can be parallel.
-            // Ordered dithering. We are only operating on a single pixel.
-            for (int y = interest.Top; y < interest.Bottom; y++)
-            {
-                Span<TPixel> row = source.GetPixelRowSpan(y);
-                int offset = y * width;
-
-                for (int x = interest.Left; x < interest.Right; x++)
-                {
-                    TPixel dithered = this.Dither.Dither(source, interest, row[x], default, x, y, bitDepth);
-                    output[offset + x] = this.GetQuantizedColor(dithered, out TPixel _);
-                }
-            }
-        }
-
-        /// <inheritdoc/>
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        protected override ReadOnlyMemory<TPixel> GetPalette() => this.palette;
+        [MethodImpl(InliningOptions.ShortMethod)]
+        protected override ReadOnlyMemory<TPixel> GenerateQuantizedPalette() => this.palette;
     }
 }

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

@@ -35,14 +35,16 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
         /// <inheritdoc />
         protected override void OnFrameApply(ImageFrame<TPixel> source)
         {
+            var interest = Rectangle.Intersect(source.Bounds(), this.SourceRectangle);
+
             Configuration configuration = this.Configuration;
             using IFrameQuantizer<TPixel> frameQuantizer = this.quantizer.CreateFrameQuantizer<TPixel>(configuration);
-            using IQuantizedFrame<TPixel> quantized = frameQuantizer.QuantizeFrame(source);
+            using IQuantizedFrame<TPixel> quantized = frameQuantizer.QuantizeFrame(source, interest);
 
             var operation = new RowIntervalOperation(this.SourceRectangle, source, quantized);
             ParallelRowIterator.IterateRows(
                 configuration,
-                this.SourceRectangle,
+                interest,
                 in operation);
         }
 
@@ -71,14 +73,15 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
                 ReadOnlySpan<byte> quantizedPixelSpan = this.quantized.GetPixelSpan();
                 ReadOnlySpan<TPixel> paletteSpan = this.quantized.Palette.Span;
 
+                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;
 
-                    for (int x = this.bounds.X; x < this.bounds.Right; x++)
+                    for (int x = this.bounds.Left; x < this.bounds.Right; x++)
                     {
-                        int i = x + yy;
+                        int i = yy + x - offset;
                         row[x] = paletteSpan[Math.Min(this.maxPaletteIndex, quantizedPixelSpan[i])];
                     }
                 }

src/ImageSharp/Processing/Processors/Quantization/QuantizedFrame{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;
@@ -13,7 +13,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
     /// Represents a quantized image frame where the pixels indexed by a color palette.
     /// </summary>
     /// <typeparam name="TPixel">The pixel format.</typeparam>
-    public class QuantizedFrame<TPixel> : IQuantizedFrame<TPixel>
+    public sealed class QuantizedFrame<TPixel> : IQuantizedFrame<TPixel>
         where TPixel : struct, IPixel<TPixel>
     {
         private IMemoryOwner<byte> pixels;
@@ -67,8 +67,8 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
         }
 
         /// <summary>
-        /// Get the non-readonly span of pixel data so <see cref="FrameQuantizer{TPixel}"/> can fill it.
+        /// Get the non-readonly memory of pixel data so <see cref="FrameQuantizer{TPixel}"/> can fill it.
         /// </summary>
-        internal Span<byte> GetWritablePixelSpan() => this.pixels.GetSpan();
+        internal Memory<byte> GetWritablePixelMemory() => this.pixels.Memory;
     }
-}
+}

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

@@ -147,10 +147,10 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
             base.Dispose(true);
         }
 
-        internal ReadOnlyMemory<TPixel> AotGetPalette() => this.GetPalette();
+        internal ReadOnlyMemory<TPixel> AotGetPalette() => this.GenerateQuantizedPalette();
 
         /// <inheritdoc/>
-        protected override ReadOnlyMemory<TPixel> GetPalette()
+        protected override ReadOnlyMemory<TPixel> GenerateQuantizedPalette()
         {
             if (this.palette is null)
             {
@@ -175,16 +175,16 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
         }
 
         /// <inheritdoc/>
-        protected override void FirstPass(ImageFrame<TPixel> source, int width, int height)
+        protected override void FirstPass(ImageFrame<TPixel> source, Rectangle bounds)
         {
-            this.Build3DHistogram(source, width, height);
+            this.Build3DHistogram(source, bounds);
             this.Get3DMoments(this.memoryAllocator);
             this.BuildCube();
         }
 
         /// <inheritdoc/>
         [MethodImpl(InliningOptions.ShortMethod)]
-        protected override byte GetQuantizedColor(TPixel color, out TPixel match)
+        protected override byte GetQuantizedColor(TPixel color, ReadOnlySpan<TPixel> palette, out TPixel match)
         {
             if (!this.DoDither)
             {
@@ -199,11 +199,11 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
 
                 ReadOnlySpan<byte> tagSpan = this.tag.GetSpan();
                 var index = tagSpan[GetPaletteIndex(r + 1, g + 1, b + 1, a + 1)];
-                match = this.GetPalette().Span[index];
+                match = palette[index];
                 return index;
             }
 
-            return base.GetQuantizedColor(color, out match);
+            return base.GetQuantizedColor(color, palette, out match);
         }
 
         /// <summary>
@@ -378,9 +378,8 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
         /// Builds a 3-D color histogram of <c>counts, r/g/b, c^2</c>.
         /// </summary>
         /// <param name="source">The source data.</param>
-        /// <param name="width">The width in pixels of the image.</param>
-        /// <param name="height">The height in pixels of the image.</param>
-        private void Build3DHistogram(ImageFrame<TPixel> source, int width, int height)
+        /// <param name="bounds">The bounds within the source image to quantize.</param>
+        private void Build3DHistogram(ImageFrame<TPixel> source, Rectangle bounds)
         {
             Span<Moment> momentSpan = this.moments.GetSpan();
 
@@ -390,15 +389,16 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
             Span<Rgba32> rgbaSpan = rgbaBuffer.GetSpan();
             ref Rgba32 scanBaseRef = ref MemoryMarshal.GetReference(rgbaSpan);
 
-            for (int y = 0; y < height; y++)
+            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);
 
                 // And loop through each column
-                for (int x = 0; x < width; x++)
+                for (int x = bounds.Left; x < bounds.Right; x++)
                 {
-                    ref Rgba32 rgba = ref Unsafe.Add(ref scanBaseRef, x);
+                    ref Rgba32 rgba = ref Unsafe.Add(ref scanBaseRef, x - offset);
 
                     int r = (rgba.R >> (8 - IndexBits)) + 1;
                     int g = (rgba.G >> (8 - IndexBits)) + 1;

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.Diffuse());
+                image.Mutate(x => x.Dither());
 
                 return image.Size();
             }

tests/ImageSharp.Tests/Processing/Binarization/BinaryDitherTest.cs

@@ -1,106 +0,0 @@
-// Copyright (c) Six Labors and contributors.
-// Licensed under the Apache License, Version 2.0.
-
-using SixLabors.ImageSharp.Processing;
-using SixLabors.ImageSharp.Processing.Processors.Binarization;
-using SixLabors.ImageSharp.Processing.Processors.Dithering;
-
-using Xunit;
-
-namespace SixLabors.ImageSharp.Tests.Processing.Binarization
-{
-    public class BinaryDitherTest : BaseImageOperationsExtensionTest
-    {
-        private readonly IDither orderedDither;
-        private readonly IDither errorDiffuser;
-
-        public BinaryDitherTest()
-        {
-            this.orderedDither = KnownDitherers.BayerDither4x4;
-            this.errorDiffuser = KnownDiffusers.FloydSteinberg;
-        }
-
-        [Fact]
-        public void BinaryDither_CorrectProcessor()
-        {
-            this.operations.BinaryDither(this.orderedDither);
-            BinaryOrderedDitherProcessor p = this.Verify<BinaryOrderedDitherProcessor>();
-            Assert.Equal(this.orderedDither, p.Dither);
-            Assert.Equal(Color.White, p.UpperColor);
-            Assert.Equal(Color.Black, p.LowerColor);
-        }
-
-        [Fact]
-        public void BinaryDither_rect_CorrectProcessor()
-        {
-            this.operations.BinaryDither(this.orderedDither, this.rect);
-            BinaryOrderedDitherProcessor p = this.Verify<BinaryOrderedDitherProcessor>(this.rect);
-            Assert.Equal(this.orderedDither, p.Dither);
-            Assert.Equal(Color.White, p.UpperColor);
-            Assert.Equal(Color.Black, p.LowerColor);
-        }
-
-        [Fact]
-        public void BinaryDither_index_CorrectProcessor()
-        {
-            this.operations.BinaryDither(this.orderedDither, Color.Yellow, Color.HotPink);
-            BinaryOrderedDitherProcessor p = this.Verify<BinaryOrderedDitherProcessor>();
-            Assert.Equal(this.orderedDither, p.Dither);
-            Assert.Equal(Color.Yellow, p.UpperColor);
-            Assert.Equal(Color.HotPink, p.LowerColor);
-        }
-
-        [Fact]
-        public void BinaryDither_index_rect_CorrectProcessor()
-        {
-            this.operations.BinaryDither(this.orderedDither, Color.Yellow, Color.HotPink, this.rect);
-            BinaryOrderedDitherProcessor p = this.Verify<BinaryOrderedDitherProcessor>(this.rect);
-            Assert.Equal(this.orderedDither, p.Dither);
-            Assert.Equal(Color.HotPink, p.LowerColor);
-        }
-
-        [Fact]
-        public void BinaryDither_ErrorDiffuser_CorrectProcessor()
-        {
-            this.operations.BinaryDiffuse(this.errorDiffuser, .4F);
-            BinaryErrorDiffusionProcessor p = this.Verify<BinaryErrorDiffusionProcessor>();
-            Assert.Equal(this.errorDiffuser, p.Diffuser);
-            Assert.Equal(.4F, p.Threshold);
-            Assert.Equal(Color.White, p.UpperColor);
-            Assert.Equal(Color.Black, p.LowerColor);
-        }
-
-        [Fact]
-        public void BinaryDither_ErrorDiffuser_rect_CorrectProcessor()
-        {
-            this.operations.BinaryDiffuse(this.errorDiffuser, .3F, this.rect);
-            BinaryErrorDiffusionProcessor p = this.Verify<BinaryErrorDiffusionProcessor>(this.rect);
-            Assert.Equal(this.errorDiffuser, p.Diffuser);
-            Assert.Equal(.3F, p.Threshold);
-            Assert.Equal(Color.White, p.UpperColor);
-            Assert.Equal(Color.Black, p.LowerColor);
-        }
-
-        [Fact]
-        public void BinaryDither_ErrorDiffuser_CorrectProcessorWithColors()
-        {
-            this.operations.BinaryDiffuse(this.errorDiffuser, .5F, Color.HotPink, Color.Yellow);
-            BinaryErrorDiffusionProcessor p = this.Verify<BinaryErrorDiffusionProcessor>();
-            Assert.Equal(this.errorDiffuser, p.Diffuser);
-            Assert.Equal(.5F, p.Threshold);
-            Assert.Equal(Color.HotPink, p.UpperColor);
-            Assert.Equal(Color.Yellow, p.LowerColor);
-        }
-
-        [Fact]
-        public void BinaryDither_ErrorDiffuser_rect_CorrectProcessorWithColors()
-        {
-            this.operations.BinaryDiffuse(this.errorDiffuser, .5F, Color.HotPink, Color.Yellow, this.rect);
-            BinaryErrorDiffusionProcessor p = this.Verify<BinaryErrorDiffusionProcessor>(this.rect);
-            Assert.Equal(this.errorDiffuser, p.Diffuser);
-            Assert.Equal(.5F, p.Threshold);
-            Assert.Equal(Color.HotPink, p.UpperColor);
-            Assert.Equal(Color.Yellow, p.LowerColor);
-        }
-    }
-}

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

@@ -2,10 +2,8 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System;
-
 using SixLabors.ImageSharp.Processing;
 using SixLabors.ImageSharp.Processing.Processors.Dithering;
-
 using Xunit;
 
 namespace SixLabors.ImageSharp.Tests.Processing.Binarization
@@ -32,14 +30,14 @@ namespace SixLabors.ImageSharp.Tests.Processing.Binarization
         public DitherTest()
         {
             this.orderedDither = KnownDitherers.BayerDither4x4;
-            this.errorDiffuser = KnownDiffusers.FloydSteinberg;
+            this.errorDiffuser = KnownDitherers.FloydSteinberg;
         }
 
         [Fact]
         public void Dither_CorrectProcessor()
         {
             this.operations.Dither(this.orderedDither);
-            OrderedDitherPaletteProcessor p = this.Verify<OrderedDitherPaletteProcessor>();
+            PaletteDitherProcessor p = this.Verify<PaletteDitherProcessor>();
             Assert.Equal(this.orderedDither, p.Dither);
             Assert.Equal(Color.WebSafePalette, p.Palette);
         }
@@ -48,7 +46,7 @@ namespace SixLabors.ImageSharp.Tests.Processing.Binarization
         public void Dither_rect_CorrectProcessor()
         {
             this.operations.Dither(this.orderedDither, this.rect);
-            OrderedDitherPaletteProcessor p = this.Verify<OrderedDitherPaletteProcessor>(this.rect);
+            PaletteDitherProcessor p = this.Verify<PaletteDitherProcessor>(this.rect);
             Assert.Equal(this.orderedDither, p.Dither);
             Assert.Equal(Color.WebSafePalette, p.Palette);
         }
@@ -57,7 +55,7 @@ namespace SixLabors.ImageSharp.Tests.Processing.Binarization
         public void Dither_index_CorrectProcessor()
         {
             this.operations.Dither(this.orderedDither, this.testPalette);
-            OrderedDitherPaletteProcessor p = this.Verify<OrderedDitherPaletteProcessor>();
+            PaletteDitherProcessor p = this.Verify<PaletteDitherProcessor>();
             Assert.Equal(this.orderedDither, p.Dither);
             Assert.Equal(this.testPalette, p.Palette);
         }
@@ -66,7 +64,7 @@ namespace SixLabors.ImageSharp.Tests.Processing.Binarization
         public void Dither_index_rect_CorrectProcessor()
         {
             this.operations.Dither(this.orderedDither, this.testPalette, this.rect);
-            OrderedDitherPaletteProcessor p = this.Verify<OrderedDitherPaletteProcessor>(this.rect);
+            PaletteDitherProcessor p = this.Verify<PaletteDitherProcessor>(this.rect);
             Assert.Equal(this.orderedDither, p.Dither);
             Assert.Equal(this.testPalette, p.Palette);
         }
@@ -74,40 +72,36 @@ namespace SixLabors.ImageSharp.Tests.Processing.Binarization
         [Fact]
         public void Dither_ErrorDiffuser_CorrectProcessor()
         {
-            this.operations.Diffuse(this.errorDiffuser, .4F);
-            ErrorDiffusionPaletteProcessor p = this.Verify<ErrorDiffusionPaletteProcessor>();
-            Assert.Equal(this.errorDiffuser, p.Diffuser);
-            Assert.Equal(.4F, p.Threshold);
+            this.operations.Dither(this.errorDiffuser);
+            PaletteDitherProcessor p = this.Verify<PaletteDitherProcessor>();
+            Assert.Equal(this.errorDiffuser, p.Dither);
             Assert.Equal(Color.WebSafePalette, p.Palette);
         }
 
         [Fact]
         public void Dither_ErrorDiffuser_rect_CorrectProcessor()
         {
-            this.operations.Diffuse(this.errorDiffuser, .3F, this.rect);
-            ErrorDiffusionPaletteProcessor p = this.Verify<ErrorDiffusionPaletteProcessor>(this.rect);
-            Assert.Equal(this.errorDiffuser, p.Diffuser);
-            Assert.Equal(.3F, p.Threshold);
+            this.operations.Dither(this.errorDiffuser, this.rect);
+            PaletteDitherProcessor p = this.Verify<PaletteDitherProcessor>(this.rect);
+            Assert.Equal(this.errorDiffuser, p.Dither);
             Assert.Equal(Color.WebSafePalette, p.Palette);
         }
 
         [Fact]
         public void Dither_ErrorDiffuser_CorrectProcessorWithColors()
         {
-            this.operations.Diffuse(this.errorDiffuser, .5F, this.testPalette);
-            ErrorDiffusionPaletteProcessor p = this.Verify<ErrorDiffusionPaletteProcessor>();
-            Assert.Equal(this.errorDiffuser, p.Diffuser);
-            Assert.Equal(.5F, p.Threshold);
+            this.operations.Dither(this.errorDiffuser, this.testPalette);
+            PaletteDitherProcessor p = this.Verify<PaletteDitherProcessor>();
+            Assert.Equal(this.errorDiffuser, p.Dither);
             Assert.Equal(this.testPalette, p.Palette);
         }
 
         [Fact]
         public void Dither_ErrorDiffuser_rect_CorrectProcessorWithColors()
         {
-            this.operations.Diffuse(this.errorDiffuser, .5F, this.testPalette, this.rect);
-            ErrorDiffusionPaletteProcessor p = this.Verify<ErrorDiffusionPaletteProcessor>(this.rect);
-            Assert.Equal(this.errorDiffuser, p.Diffuser);
-            Assert.Equal(.5F, p.Threshold);
+            this.operations.Dither(this.errorDiffuser, this.testPalette, this.rect);
+            PaletteDitherProcessor p = this.Verify<PaletteDitherProcessor>(this.rect);
+            Assert.Equal(this.errorDiffuser, p.Dither);
             Assert.Equal(this.testPalette, p.Palette);
         }
     }

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

@@ -28,22 +28,22 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Binarization
 
         public static readonly TheoryData<string, IDither> ErrorDiffusers = new TheoryData<string, IDither>
         {
-            { "Atkinson", KnownDiffusers.Atkinson },
-            { "Burks", KnownDiffusers.Burks },
-            { "FloydSteinberg", KnownDiffusers.FloydSteinberg },
-            { "JarvisJudiceNinke", KnownDiffusers.JarvisJudiceNinke },
-            { "Sierra2", KnownDiffusers.Sierra2 },
-            { "Sierra3", KnownDiffusers.Sierra3 },
-            { "SierraLite", KnownDiffusers.SierraLite },
-            { "StevensonArce", KnownDiffusers.StevensonArce },
-            { "Stucki", KnownDiffusers.Stucki },
+            { "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 },
         };
 
         public const PixelTypes TestPixelTypes = PixelTypes.Rgba32 | PixelTypes.Bgra32 | PixelTypes.Rgb24;
 
         private static IDither DefaultDitherer => KnownDitherers.BayerDither4x4;
 
-        private static IDither DefaultErrorDiffuser => KnownDiffusers.Atkinson;
+        private static IDither DefaultErrorDiffuser => KnownDitherers.Atkinson;
 
         [Theory]
         [WithFileCollection(nameof(CommonTestImages), nameof(OrderedDitherers), PixelTypes.Rgba32)]
@@ -66,7 +66,7 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Binarization
         {
             using (Image<TPixel> image = provider.GetImage())
             {
-                image.Mutate(x => x.BinaryDiffuse(diffuser, .5F));
+                image.Mutate(x => x.BinaryDither(diffuser));
                 image.DebugSave(provider, name);
             }
         }
@@ -90,7 +90,7 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Binarization
         {
             using (Image<TPixel> image = provider.GetImage())
             {
-                image.Mutate(x => x.BinaryDiffuse(DefaultErrorDiffuser, 0.5f));
+                image.Mutate(x => x.BinaryDither(DefaultErrorDiffuser));
                 image.DebugSave(provider);
             }
         }
@@ -122,7 +122,7 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Binarization
             {
                 var bounds = new Rectangle(10, 10, image.Width / 2, image.Height / 2);
 
-                image.Mutate(x => x.BinaryDiffuse(DefaultErrorDiffuser, .5F, bounds));
+                image.Mutate(x => x.BinaryDither(DefaultErrorDiffuser, bounds));
                 image.DebugSave(provider);
 
                 ImageComparer.Tolerant().VerifySimilarityIgnoreRegion(source, image, bounds);

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

@@ -20,15 +20,15 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Binarization
         public static readonly TheoryData<IDither> ErrorDiffusers
             = new TheoryData<IDither>
             {
-                KnownDiffusers.Atkinson,
-                KnownDiffusers.Burks,
-                KnownDiffusers.FloydSteinberg,
-                KnownDiffusers.JarvisJudiceNinke,
-                KnownDiffusers.Sierra2,
-                KnownDiffusers.Sierra3,
-                KnownDiffusers.SierraLite,
-                KnownDiffusers.StevensonArce,
-                KnownDiffusers.Stucki,
+                KnownDitherers.Atkinson,
+                KnownDitherers.Burks,
+                KnownDitherers.FloydSteinberg,
+                KnownDitherers.JarvisJudiceNinke,
+                KnownDitherers.Sierra2,
+                KnownDitherers.Sierra3,
+                KnownDitherers.SierraLite,
+                KnownDitherers.StevensonArce,
+                KnownDitherers.Stucki,
             };
 
         public static readonly TheoryData<IDither> OrderedDitherers
@@ -44,7 +44,7 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Binarization
 
         private static IDither DefaultDitherer => KnownDitherers.BayerDither4x4;
 
-        private static IDither DefaultErrorDiffuser => KnownDiffusers.Atkinson;
+        private static IDither DefaultErrorDiffuser => KnownDitherers.Atkinson;
 
         /// <summary>
         /// The output is visually correct old 32bit runtime,
@@ -64,7 +64,7 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Binarization
             }
 
             provider.RunRectangleConstrainedValidatingProcessorTest(
-                (x, rect) => x.Diffuse(DefaultErrorDiffuser, .5F, rect),
+                (x, rect) => x.Dither(DefaultErrorDiffuser, rect),
                 comparer: ValidatorComparer);
         }
 
@@ -95,7 +95,7 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Binarization
 
             // Increased tolerance because of compatibility issues on .NET 4.6.2:
             var comparer = ImageComparer.TolerantPercentage(1f);
-            provider.RunValidatingProcessorTest(x => x.Diffuse(DefaultErrorDiffuser, 0.5f), comparer: comparer);
+            provider.RunValidatingProcessorTest(x => x.Dither(DefaultErrorDiffuser), comparer: comparer);
         }
 
         [Theory]
@@ -111,7 +111,7 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Binarization
             }
 
             provider.RunValidatingProcessorTest(
-                x => x.Diffuse(diffuser, 0.5f),
+                x => x.Dither(diffuser),
                 testOutputDetails: diffuser.GetType().Name,
                 comparer: ValidatorComparer,
                 appendPixelTypeToFileName: false);

tests/ImageSharp.Tests/Processing/Processors/Quantization/OctreeQuantizerTests.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;
@@ -16,19 +16,19 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Quantization
             var quantizer = new OctreeQuantizer(128);
 
             Assert.Equal(128, quantizer.MaxColors);
-            Assert.Equal(KnownDiffusers.FloydSteinberg, quantizer.Diffuser);
+            Assert.Equal(KnownDitherers.FloydSteinberg, quantizer.Dither);
 
             quantizer = new OctreeQuantizer(false);
             Assert.Equal(QuantizerConstants.MaxColors, quantizer.MaxColors);
-            Assert.Null(quantizer.Diffuser);
+            Assert.Null(quantizer.Dither);
 
-            quantizer = new OctreeQuantizer(KnownDiffusers.Atkinson);
+            quantizer = new OctreeQuantizer(KnownDitherers.Atkinson);
             Assert.Equal(QuantizerConstants.MaxColors, quantizer.MaxColors);
-            Assert.Equal(KnownDiffusers.Atkinson, quantizer.Diffuser);
+            Assert.Equal(KnownDitherers.Atkinson, quantizer.Dither);
 
-            quantizer = new OctreeQuantizer(KnownDiffusers.Atkinson, 128);
+            quantizer = new OctreeQuantizer(KnownDitherers.Atkinson, 128);
             Assert.Equal(128, quantizer.MaxColors);
-            Assert.Equal(KnownDiffusers.Atkinson, quantizer.Diffuser);
+            Assert.Equal(KnownDitherers.Atkinson, quantizer.Dither);
         }
 
         [Fact]
@@ -38,21 +38,21 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Quantization
             IFrameQuantizer<Rgba32> frameQuantizer = quantizer.CreateFrameQuantizer<Rgba32>(Configuration.Default);
 
             Assert.NotNull(frameQuantizer);
-            Assert.True(frameQuantizer.Dither);
-            Assert.Equal(KnownDiffusers.FloydSteinberg, frameQuantizer.Dither);
+            Assert.True(frameQuantizer.DoDither);
+            Assert.Equal(KnownDitherers.FloydSteinberg, frameQuantizer.Dither);
 
             quantizer = new OctreeQuantizer(false);
             frameQuantizer = quantizer.CreateFrameQuantizer<Rgba32>(Configuration.Default);
 
             Assert.NotNull(frameQuantizer);
-            Assert.False(frameQuantizer.Dither);
+            Assert.False(frameQuantizer.DoDither);
             Assert.Null(frameQuantizer.Dither);
 
-            quantizer = new OctreeQuantizer(KnownDiffusers.Atkinson);
+            quantizer = new OctreeQuantizer(KnownDitherers.Atkinson);
             frameQuantizer = quantizer.CreateFrameQuantizer<Rgba32>(Configuration.Default);
             Assert.NotNull(frameQuantizer);
-            Assert.True(frameQuantizer.Dither);
-            Assert.Equal(KnownDiffusers.Atkinson, frameQuantizer.Dither);
+            Assert.True(frameQuantizer.DoDither);
+            Assert.Equal(KnownDitherers.Atkinson, frameQuantizer.Dither);
         }
     }
 }

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(KnownDiffusers.FloydSteinberg, quantizer.Diffuser);
+            Assert.Equal(KnownDitherers.FloydSteinberg, quantizer.Dither);
 
             quantizer = new PaletteQuantizer(Rgb, false);
             Assert.Equal(Rgb, quantizer.Palette);
-            Assert.Null(quantizer.Diffuser);
+            Assert.Null(quantizer.Dither);
 
-            quantizer = new PaletteQuantizer(Rgb, KnownDiffusers.Atkinson);
+            quantizer = new PaletteQuantizer(Rgb, KnownDitherers.Atkinson);
             Assert.Equal(Rgb, quantizer.Palette);
-            Assert.Equal(KnownDiffusers.Atkinson, quantizer.Diffuser);
+            Assert.Equal(KnownDitherers.Atkinson, quantizer.Dither);
         }
 
         [Fact]
@@ -36,35 +36,35 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Quantization
             IFrameQuantizer<Rgba32> frameQuantizer = quantizer.CreateFrameQuantizer<Rgba32>(Configuration.Default);
 
             Assert.NotNull(frameQuantizer);
-            Assert.True(frameQuantizer.Dither);
-            Assert.Equal(KnownDiffusers.FloydSteinberg, frameQuantizer.Dither);
+            Assert.True(frameQuantizer.DoDither);
+            Assert.Equal(KnownDitherers.FloydSteinberg, frameQuantizer.Dither);
 
             quantizer = new PaletteQuantizer(Rgb, false);
             frameQuantizer = quantizer.CreateFrameQuantizer<Rgba32>(Configuration.Default);
 
             Assert.NotNull(frameQuantizer);
-            Assert.False(frameQuantizer.Dither);
+            Assert.False(frameQuantizer.DoDither);
             Assert.Null(frameQuantizer.Dither);
 
-            quantizer = new PaletteQuantizer(Rgb, KnownDiffusers.Atkinson);
+            quantizer = new PaletteQuantizer(Rgb, KnownDitherers.Atkinson);
             frameQuantizer = quantizer.CreateFrameQuantizer<Rgba32>(Configuration.Default);
             Assert.NotNull(frameQuantizer);
-            Assert.True(frameQuantizer.Dither);
-            Assert.Equal(KnownDiffusers.Atkinson, frameQuantizer.Dither);
+            Assert.True(frameQuantizer.DoDither);
+            Assert.Equal(KnownDitherers.Atkinson, frameQuantizer.Dither);
         }
 
         [Fact]
         public void KnownQuantizersWebSafeTests()
         {
             IQuantizer quantizer = KnownQuantizers.WebSafe;
-            Assert.Equal(KnownDiffusers.FloydSteinberg, quantizer.Diffuser);
+            Assert.Equal(KnownDitherers.FloydSteinberg, quantizer.Dither);
         }
 
         [Fact]
         public void KnownQuantizersWernerTests()
         {
             IQuantizer quantizer = KnownQuantizers.Werner;
-            Assert.Equal(KnownDiffusers.FloydSteinberg, quantizer.Diffuser);
+            Assert.Equal(KnownDitherers.FloydSteinberg, quantizer.Dither);
         }
     }
 }

tests/ImageSharp.Tests/Processing/Processors/Quantization/WuQuantizerTests.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;
@@ -16,19 +16,19 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Quantization
             var quantizer = new WuQuantizer(128);
 
             Assert.Equal(128, quantizer.MaxColors);
-            Assert.Equal(KnownDiffusers.FloydSteinberg, quantizer.Diffuser);
+            Assert.Equal(KnownDitherers.FloydSteinberg, quantizer.Dither);
 
             quantizer = new WuQuantizer(false);
             Assert.Equal(QuantizerConstants.MaxColors, quantizer.MaxColors);
-            Assert.Null(quantizer.Diffuser);
+            Assert.Null(quantizer.Dither);
 
-            quantizer = new WuQuantizer(KnownDiffusers.Atkinson);
+            quantizer = new WuQuantizer(KnownDitherers.Atkinson);
             Assert.Equal(QuantizerConstants.MaxColors, quantizer.MaxColors);
-            Assert.Equal(KnownDiffusers.Atkinson, quantizer.Diffuser);
+            Assert.Equal(KnownDitherers.Atkinson, quantizer.Dither);
 
-            quantizer = new WuQuantizer(KnownDiffusers.Atkinson, 128);
+            quantizer = new WuQuantizer(KnownDitherers.Atkinson, 128);
             Assert.Equal(128, quantizer.MaxColors);
-            Assert.Equal(KnownDiffusers.Atkinson, quantizer.Diffuser);
+            Assert.Equal(KnownDitherers.Atkinson, quantizer.Dither);
         }
 
         [Fact]
@@ -38,21 +38,21 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Quantization
             IFrameQuantizer<Rgba32> frameQuantizer = quantizer.CreateFrameQuantizer<Rgba32>(Configuration.Default);
 
             Assert.NotNull(frameQuantizer);
-            Assert.True(frameQuantizer.Dither);
-            Assert.Equal(KnownDiffusers.FloydSteinberg, frameQuantizer.Dither);
+            Assert.True(frameQuantizer.DoDither);
+            Assert.Equal(KnownDitherers.FloydSteinberg, frameQuantizer.Dither);
 
             quantizer = new WuQuantizer(false);
             frameQuantizer = quantizer.CreateFrameQuantizer<Rgba32>(Configuration.Default);
 
             Assert.NotNull(frameQuantizer);
-            Assert.False(frameQuantizer.Dither);
+            Assert.False(frameQuantizer.DoDither);
             Assert.Null(frameQuantizer.Dither);
 
-            quantizer = new WuQuantizer(KnownDiffusers.Atkinson);
+            quantizer = new WuQuantizer(KnownDitherers.Atkinson);
             frameQuantizer = quantizer.CreateFrameQuantizer<Rgba32>(Configuration.Default);
             Assert.NotNull(frameQuantizer);
-            Assert.True(frameQuantizer.Dither);
-            Assert.Equal(KnownDiffusers.Atkinson, frameQuantizer.Dither);
+            Assert.True(frameQuantizer.DoDither);
+            Assert.Equal(KnownDitherers.Atkinson, frameQuantizer.Dither);
         }
     }
 }

tests/ImageSharp.Tests/Quantization/QuantizedImageTests.cs

@@ -22,15 +22,30 @@ namespace SixLabors.ImageSharp.Tests
             var octree = new OctreeQuantizer();
             var wu = new WuQuantizer();
 
-            Assert.NotNull(werner.Diffuser);
-            Assert.NotNull(webSafe.Diffuser);
-            Assert.NotNull(octree.Diffuser);
-            Assert.NotNull(wu.Diffuser);
-
-            Assert.True(werner.CreateFrameQuantizer<Rgba32>(this.Configuration).Dither);
-            Assert.True(webSafe.CreateFrameQuantizer<Rgba32>(this.Configuration).Dither);
-            Assert.True(octree.CreateFrameQuantizer<Rgba32>(this.Configuration).Dither);
-            Assert.True(wu.CreateFrameQuantizer<Rgba32>(this.Configuration).Dither);
+            Assert.NotNull(werner.Dither);
+            Assert.NotNull(webSafe.Dither);
+            Assert.NotNull(octree.Dither);
+            Assert.NotNull(wu.Dither);
+
+            using (IFrameQuantizer<Rgba32> quantizer = werner.CreateFrameQuantizer<Rgba32>(this.Configuration))
+            {
+                Assert.True(quantizer.DoDither);
+            }
+
+            using (IFrameQuantizer<Rgba32> quantizer = webSafe.CreateFrameQuantizer<Rgba32>(this.Configuration))
+            {
+                Assert.True(quantizer.DoDither);
+            }
+
+            using (IFrameQuantizer<Rgba32> quantizer = octree.CreateFrameQuantizer<Rgba32>(this.Configuration))
+            {
+                Assert.True(quantizer.DoDither);
+            }
+
+            using (IFrameQuantizer<Rgba32> quantizer = wu.CreateFrameQuantizer<Rgba32>(this.Configuration))
+            {
+                Assert.True(quantizer.DoDither);
+            }
         }
 
         [Theory]
@@ -49,11 +64,12 @@ namespace SixLabors.ImageSharp.Tests
 
                 foreach (ImageFrame<TPixel> frame in image.Frames)
                 {
-                    IQuantizedFrame<TPixel> quantized =
-                        quantizer.CreateFrameQuantizer<TPixel>(this.Configuration).QuantizeFrame(frame);
-
-                    int index = this.GetTransparentIndex(quantized);
-                    Assert.Equal(index, quantized.GetPixelSpan()[0]);
+                    using (IFrameQuantizer<TPixel> frameQuantizer = quantizer.CreateFrameQuantizer<TPixel>(this.Configuration))
+                    using (IQuantizedFrame<TPixel> quantized = frameQuantizer.QuantizeFrame(frame, frame.Bounds()))
+                    {
+                        int index = this.GetTransparentIndex(quantized);
+                        Assert.Equal(index, quantized.GetPixelSpan()[0]);
+                    }
                 }
             }
         }
@@ -72,11 +88,12 @@ namespace SixLabors.ImageSharp.Tests
 
                 foreach (ImageFrame<TPixel> frame in image.Frames)
                 {
-                    IQuantizedFrame<TPixel> quantized =
-                        quantizer.CreateFrameQuantizer<TPixel>(this.Configuration).QuantizeFrame(frame);
-
-                    int index = this.GetTransparentIndex(quantized);
-                    Assert.Equal(index, quantized.GetPixelSpan()[0]);
+                    using (IFrameQuantizer<TPixel> frameQuantizer = quantizer.CreateFrameQuantizer<TPixel>(this.Configuration))
+                    using (IQuantizedFrame<TPixel> quantized = frameQuantizer.QuantizeFrame(frame, frame.Bounds()))
+                    {
+                        int index = this.GetTransparentIndex(quantized);
+                        Assert.Equal(index, quantized.GetPixelSpan()[0]);
+                    }
                 }
             }
         }

tests/ImageSharp.Tests/Quantization/WuQuantizerTests.cs

@@ -17,15 +17,17 @@ namespace SixLabors.ImageSharp.Tests.Quantization
             Configuration config = Configuration.Default;
             var quantizer = new WuQuantizer(false);
 
-            using (var image = new Image<Rgba32>(config, 1, 1, Color.Black))
-            using (IQuantizedFrame<Rgba32> result = quantizer.CreateFrameQuantizer<Rgba32>(config).QuantizeFrame(image.Frames[0]))
-            {
-                Assert.Equal(1, result.Palette.Length);
-                Assert.Equal(1, result.GetPixelSpan().Length);
+            using var image = new Image<Rgba32>(config, 1, 1, Color.Black);
+            ImageFrame<Rgba32> frame = image.Frames.RootFrame;
 
-                Assert.Equal(Color.Black, (Color)result.Palette.Span[0]);
-                Assert.Equal(0, result.GetPixelSpan()[0]);
-            }
+            using IFrameQuantizer<Rgba32> frameQuantizer = quantizer.CreateFrameQuantizer<Rgba32>(config);
+            using IQuantizedFrame<Rgba32> result = frameQuantizer.QuantizeFrame(frame, frame.Bounds());
+
+            Assert.Equal(1, result.Palette.Length);
+            Assert.Equal(1, result.GetPixelSpan().Length);
+
+            Assert.Equal(Color.Black, (Color)result.Palette.Span[0]);
+            Assert.Equal(0, result.GetPixelSpan()[0]);
         }
 
         [Fact]
@@ -34,15 +36,17 @@ namespace SixLabors.ImageSharp.Tests.Quantization
             Configuration config = Configuration.Default;
             var quantizer = new WuQuantizer(false);
 
-            using (var image = new Image<Rgba32>(config, 1, 1, default(Rgba32)))
-            using (IQuantizedFrame<Rgba32> result = quantizer.CreateFrameQuantizer<Rgba32>(config).QuantizeFrame(image.Frames[0]))
-            {
-                Assert.Equal(1, result.Palette.Length);
-                Assert.Equal(1, result.GetPixelSpan().Length);
+            using var image = new Image<Rgba32>(config, 1, 1, default(Rgba32));
+            ImageFrame<Rgba32> frame = image.Frames.RootFrame;
 
-                Assert.Equal(default, result.Palette.Span[0]);
-                Assert.Equal(0, result.GetPixelSpan()[0]);
-            }
+            using IFrameQuantizer<Rgba32> frameQuantizer = quantizer.CreateFrameQuantizer<Rgba32>(config);
+            using IQuantizedFrame<Rgba32> result = frameQuantizer.QuantizeFrame(frame, frame.Bounds());
+
+            Assert.Equal(1, result.Palette.Length);
+            Assert.Equal(1, result.GetPixelSpan().Length);
+
+            Assert.Equal(default, result.Palette.Span[0]);
+            Assert.Equal(0, result.GetPixelSpan()[0]);
         }
 
         [Fact]
@@ -63,46 +67,47 @@ namespace SixLabors.ImageSharp.Tests.Quantization
         [Fact]
         public void Palette256()
         {
-            using (var image = new Image<Rgba32>(1, 256))
+            using var image = new Image<Rgba32>(1, 256);
+
+            for (int i = 0; i < 256; i++)
             {
-                for (int i = 0; i < 256; i++)
-                {
-                    byte r = (byte)((i % 4) * 85);
-                    byte g = (byte)(((i / 4) % 4) * 85);
-                    byte b = (byte)(((i / 16) % 4) * 85);
-                    byte a = (byte)((i / 64) * 85);
+                byte r = (byte)((i % 4) * 85);
+                byte g = (byte)(((i / 4) % 4) * 85);
+                byte b = (byte)(((i / 16) % 4) * 85);
+                byte a = (byte)((i / 64) * 85);
 
-                    image[0, i] = new Rgba32(r, g, b, a);
-                }
+                image[0, i] = new Rgba32(r, g, b, a);
+            }
 
-                Configuration config = Configuration.Default;
-                var quantizer = new WuQuantizer(false);
-                using (IFrameQuantizer<Rgba32> frameQuantizer = quantizer.CreateFrameQuantizer<Rgba32>(config))
-                using (IQuantizedFrame<Rgba32> result = frameQuantizer.QuantizeFrame(image.Frames[0]))
-                {
-                    Assert.Equal(256, result.Palette.Length);
-                    Assert.Equal(256, result.GetPixelSpan().Length);
+            Configuration config = Configuration.Default;
+            var quantizer = new WuQuantizer(false);
 
-                    var actualImage = new Image<Rgba32>(1, 256);
+            ImageFrame<Rgba32> frame = image.Frames.RootFrame;
 
-                    ReadOnlySpan<Rgba32> paletteSpan = result.Palette.Span;
-                    int paletteCount = result.Palette.Length - 1;
-                    for (int y = 0; y < actualImage.Height; y++)
-                    {
-                        Span<Rgba32> row = actualImage.GetPixelRowSpan(y);
-                        ReadOnlySpan<byte> quantizedPixelSpan = result.GetPixelSpan();
-                        int yy = y * actualImage.Width;
+            using IFrameQuantizer<Rgba32> frameQuantizer = quantizer.CreateFrameQuantizer<Rgba32>(config);
+            using IQuantizedFrame<Rgba32> result = frameQuantizer.QuantizeFrame(frame, frame.Bounds());
 
-                        for (int x = 0; x < actualImage.Width; x++)
-                        {
-                            int i = x + yy;
-                            row[x] = paletteSpan[Math.Min(paletteCount, quantizedPixelSpan[i])];
-                        }
-                    }
+            Assert.Equal(256, result.Palette.Length);
+            Assert.Equal(256, result.GetPixelSpan().Length);
+
+            var actualImage = new Image<Rgba32>(1, 256);
 
-                    Assert.True(image.GetPixelSpan().SequenceEqual(actualImage.GetPixelSpan()));
+            ReadOnlySpan<Rgba32> paletteSpan = result.Palette.Span;
+            int paletteCount = result.Palette.Length - 1;
+            for (int y = 0; y < actualImage.Height; y++)
+            {
+                Span<Rgba32> row = actualImage.GetPixelRowSpan(y);
+                ReadOnlySpan<byte> quantizedPixelSpan = result.GetPixelSpan();
+                int yy = y * actualImage.Width;
+
+                for (int x = 0; x < actualImage.Width; x++)
+                {
+                    int i = x + yy;
+                    row[x] = paletteSpan[Math.Min(paletteCount, quantizedPixelSpan[i])];
                 }
             }
+
+            Assert.True(image.GetPixelSpan().SequenceEqual(actualImage.GetPixelSpan()));
         }
 
         [Theory]
@@ -115,11 +120,12 @@ namespace SixLabors.ImageSharp.Tests.Quantization
             {
                 Configuration config = Configuration.Default;
                 var quantizer = new WuQuantizer(false);
-                using (IFrameQuantizer<TPixel> frameQuantizer = quantizer.CreateFrameQuantizer<TPixel>(config))
-                using (IQuantizedFrame<TPixel> result = frameQuantizer.QuantizeFrame(image.Frames[0]))
-                {
-                    Assert.Equal(48, result.Palette.Length);
-                }
+                ImageFrame<TPixel> frame = image.Frames.RootFrame;
+
+                using IFrameQuantizer<TPixel> frameQuantizer = quantizer.CreateFrameQuantizer<TPixel>(config);
+                using IQuantizedFrame<TPixel> result = frameQuantizer.QuantizeFrame(frame, frame.Bounds());
+
+                Assert.Equal(48, result.Palette.Length);
             }
         }
 
@@ -144,8 +150,9 @@ namespace SixLabors.ImageSharp.Tests.Quantization
                 Configuration config = Configuration.Default;
                 var quantizer = new WuQuantizer(false);
 
+                ImageFrame<Rgba32> frame = image.Frames.RootFrame;
                 using (IFrameQuantizer<Rgba32> frameQuantizer = quantizer.CreateFrameQuantizer<Rgba32>(config))
-                using (IQuantizedFrame<Rgba32> result = frameQuantizer.QuantizeFrame(image.Frames[0]))
+                using (IQuantizedFrame<Rgba32> result = frameQuantizer.QuantizeFrame(frame, frame.Bounds()))
                 {
                     Assert.Equal(4 * 8, result.Palette.Length);
                     Assert.Equal(256, result.GetPixelSpan().Length);

tests/Images/Input/Png/CalliphoraPartial2.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:2fb48e3c495d7834df09a17d6a6cadbce047a0e791b0cb78ca3a6d334d309b13
+size 75628