introduce IQuantizedFrame<T>

src/ImageSharp/Formats/Gif/GifEncoderCore.cs

@@ -95,7 +95,7 @@ namespace SixLabors.ImageSharp.Formats.Gif
             bool useGlobalTable = this.colorTableMode == GifColorTableMode.Global;
 
             // Quantize the image returning a palette.
-            QuantizedFrame<TPixel> quantized = null;
+            IQuantizedFrame<TPixel> quantized = null;
             using (IFrameQuantizer<TPixel> frameQuantizer = this.quantizer.CreateFrameQuantizer<TPixel>(image.GetConfiguration()))
             {
                 quantized = frameQuantizer.QuantizeFrame(image.Frames.RootFrame);
@@ -141,7 +141,7 @@ namespace SixLabors.ImageSharp.Formats.Gif
             stream.WriteByte(GifConstants.EndIntroducer);
         }
 
-        private void EncodeGlobal<TPixel>(Image<TPixel> image, QuantizedFrame<TPixel> quantized, int transparencyIndex, Stream stream)
+        private void EncodeGlobal<TPixel>(Image<TPixel> image, IQuantizedFrame<TPixel> quantized, int transparencyIndex, Stream stream)
             where TPixel : struct, IPixel<TPixel>
         {
             for (int i = 0; i < image.Frames.Count; i++)
@@ -161,7 +161,7 @@ namespace SixLabors.ImageSharp.Formats.Gif
                     using (IFrameQuantizer<TPixel> palleteFrameQuantizer =
                         new PaletteFrameQuantizer<TPixel>(this.quantizer.Diffuser, quantized.Palette))
                     {
-                        using (QuantizedFrame<TPixel> paletteQuantized = palleteFrameQuantizer.QuantizeFrame(frame))
+                        using (IQuantizedFrame<TPixel> paletteQuantized = palleteFrameQuantizer.QuantizeFrame(frame))
                         {
                             this.WriteImageData(paletteQuantized, stream);
                         }
@@ -170,7 +170,7 @@ namespace SixLabors.ImageSharp.Formats.Gif
             }
         }
 
-        private void EncodeLocal<TPixel>(Image<TPixel> image, QuantizedFrame<TPixel> quantized, Stream stream)
+        private void EncodeLocal<TPixel>(Image<TPixel> image, IQuantizedFrame<TPixel> quantized, Stream stream)
             where TPixel : struct, IPixel<TPixel>
         {
             ImageFrame<TPixel> previousFrame = null;
@@ -222,7 +222,7 @@ namespace SixLabors.ImageSharp.Formats.Gif
         /// <returns>
         /// The <see cref="int"/>.
         /// </returns>
-        private int GetTransparentIndex<TPixel>(QuantizedFrame<TPixel> quantized)
+        private int GetTransparentIndex<TPixel>(IQuantizedFrame<TPixel> quantized)
             where TPixel : struct, IPixel<TPixel>
         {
             // Transparent pixels are much more likely to be found at the end of a palette
@@ -425,7 +425,7 @@ namespace SixLabors.ImageSharp.Formats.Gif
         /// <typeparam name="TPixel">The pixel format.</typeparam>
         /// <param name="image">The <see cref="ImageFrame{TPixel}"/> to encode.</param>
         /// <param name="stream">The stream to write to.</param>
-        private void WriteColorTable<TPixel>(QuantizedFrame<TPixel> image, Stream stream)
+        private void WriteColorTable<TPixel>(IQuantizedFrame<TPixel> image, Stream stream)
             where TPixel : struct, IPixel<TPixel>
         {
             // The maximum number of colors for the bit depth
@@ -447,9 +447,9 @@ namespace SixLabors.ImageSharp.Formats.Gif
         /// Writes the image pixel data to the stream.
         /// </summary>
         /// <typeparam name="TPixel">The pixel format.</typeparam>
-        /// <param name="image">The <see cref="QuantizedFrame{TPixel}"/> containing indexed pixels.</param>
+        /// <param name="image">The <see cref="IQuantizedFrame{TPixel}"/> containing indexed pixels.</param>
         /// <param name="stream">The stream to write to.</param>
-        private void WriteImageData<TPixel>(QuantizedFrame<TPixel> image, Stream stream)
+        private void WriteImageData<TPixel>(IQuantizedFrame<TPixel> image, Stream stream)
             where TPixel : struct, IPixel<TPixel>
         {
             using (var encoder = new LzwEncoder(this.memoryAllocator, (byte)this.bitDepth))

src/ImageSharp/Formats/Png/PngEncoderCore.cs

@@ -227,7 +227,7 @@ namespace SixLabors.ImageSharp.Formats.Png
 
             stream.Write(PngConstants.HeaderBytes, 0, PngConstants.HeaderBytes.Length);
 
-            QuantizedFrame<TPixel> quantized = null;
+            IQuantizedFrame<TPixel> quantized = null;
             if (this.pngColorType == PngColorType.Palette)
             {
                 byte bits = (byte)this.pngBitDepth;
@@ -511,7 +511,7 @@ namespace SixLabors.ImageSharp.Formats.Png
         /// <param name="quantized">The quantized pixels. Can be null.</param>
         /// <param name="row">The row.</param>
         /// <returns>The <see cref="IManagedByteBuffer"/></returns>
-        private IManagedByteBuffer EncodePixelRow<TPixel>(ReadOnlySpan<TPixel> rowSpan, QuantizedFrame<TPixel> quantized, int row)
+        private IManagedByteBuffer EncodePixelRow<TPixel>(ReadOnlySpan<TPixel> rowSpan, IQuantizedFrame<TPixel> quantized, int row)
             where TPixel : struct, IPixel<TPixel>
         {
             switch (this.pngColorType)
@@ -662,7 +662,7 @@ namespace SixLabors.ImageSharp.Formats.Png
         /// <typeparam name="TPixel">The pixel format.</typeparam>
         /// <param name="stream">The <see cref="Stream"/> containing image data.</param>
         /// <param name="quantized">The quantized frame.</param>
-        private void WritePaletteChunk<TPixel>(Stream stream, QuantizedFrame<TPixel> quantized)
+        private void WritePaletteChunk<TPixel>(Stream stream, IQuantizedFrame<TPixel> quantized)
             where TPixel : struct, IPixel<TPixel>
         {
             // Grab the palette and write it to the stream.
@@ -808,7 +808,7 @@ namespace SixLabors.ImageSharp.Formats.Png
         /// <param name="pixels">The image.</param>
         /// <param name="quantized">The quantized pixel data. Can be null.</param>
         /// <param name="stream">The stream.</param>
-        private void WriteDataChunks<TPixel>(ImageFrame<TPixel> pixels, QuantizedFrame<TPixel> quantized, Stream stream)
+        private void WriteDataChunks<TPixel>(ImageFrame<TPixel> pixels, IQuantizedFrame<TPixel> quantized, Stream stream)
             where TPixel : struct, IPixel<TPixel>
         {
             this.bytesPerScanline = this.CalculateScanlineLength(this.width);

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

@@ -85,7 +85,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
         }
 
         /// <inheritdoc/>
-        public QuantizedFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> image)
+        public IQuantizedFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> image)
         {
             Guard.NotNull(image, nameof(image));
 

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

@@ -31,6 +31,6 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
         /// <returns>
         /// A <see cref="QuantizedFrame{TPixel}"/> representing a quantized version of the image pixels.
         /// </returns>
-        QuantizedFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> image);
+        IQuantizedFrame<TPixel> QuantizeFrame(ImageFrame<TPixel> image);
     }
 }

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

@@ -0,0 +1,38 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+
+using SixLabors.ImageSharp.PixelFormats;
+
+namespace SixLabors.ImageSharp.Processing.Processors.Quantization
+{
+    /// <summary>
+    /// Defines an abstraction to represent a quantized image frame where the pixels indexed by a color palette.
+    /// </summary>
+    /// <typeparam name="TPixel">The pixel format.</typeparam>
+    public interface IQuantizedFrame<TPixel> : IDisposable
+        where TPixel : struct, IPixel<TPixel>
+    {
+        /// <summary>
+        /// Gets the width of this <see cref="QuantizedFrame{TPixel}"/>.
+        /// </summary>
+        int Width { get; }
+
+        /// <summary>
+        /// Gets the height of this <see cref="QuantizedFrame{TPixel}"/>.
+        /// </summary>
+        int Height { get; }
+
+        /// <summary>
+        /// Gets the color palette of this <see cref="QuantizedFrame{TPixel}"/>.
+        /// </summary>
+        ReadOnlyMemory<TPixel> Palette { get; }
+
+        /// <summary>
+        /// Gets the pixels of this <see cref="QuantizedFrame{TPixel}"/>.
+        /// </summary>
+        /// <returns>The <see cref="Span{T}"/>The pixel span.</returns>
+        ReadOnlySpan<byte> GetPixelSpan();
+    }
+}

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

@@ -31,8 +31,8 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
         /// <inheritdoc />
         protected override void OnFrameApply(ImageFrame<TPixel> source, Rectangle sourceRectangle, Configuration configuration)
         {
-            using (IFrameQuantizer<TPixel> executor = this.quantizer.CreateFrameQuantizer<TPixel>(configuration))
+            using (IFrameQuantizer<TPixel> frameQuantizer = this.quantizer.CreateFrameQuantizer<TPixel>(configuration))
-            using (QuantizedFrame<TPixel> quantized = executor.QuantizeFrame(source))
+            using (IQuantizedFrame<TPixel> quantized = frameQuantizer.QuantizeFrame(source))
             {
                 int paletteCount = quantized.Palette.Length - 1;
 

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

@@ -0,0 +1,29 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+using System.Runtime.CompilerServices;
+
+using SixLabors.ImageSharp.PixelFormats;
+
+namespace SixLabors.ImageSharp.Processing.Processors.Quantization
+{
+    /// <summary>
+    /// Contains extension methods for <see cref="IQuantizedFrame{TPixel}"/>.
+    /// </summary>
+    public static class QuantizedFrameExtensions
+    {
+        /// <summary>
+        /// Gets the representation of the pixels as a <see cref="Span{T}"/> of contiguous memory
+        /// at row <paramref name="rowIndex"/> beginning from the the first pixel on that row.
+        /// </summary>
+        /// <param name="frame">The <see cref="IQuantizedFrame{TPixel}"/>.</param>
+        /// <param name="rowIndex">The row.</param>
+        /// <typeparam name="TPixel">The pixel type.</typeparam>
+        /// <returns>The pixel row as a <see cref="ReadOnlySpan{T}"/>.</returns>
+        [MethodImpl(InliningOptions.ShortMethod)]
+        public static ReadOnlySpan<byte> GetRowSpan<TPixel>(this IQuantizedFrame<TPixel> frame, int rowIndex)
+            where TPixel : struct, IPixel<TPixel>
+            => frame.GetPixelSpan().Slice(rowIndex * frame.Width, frame.Width);
+    }
+}

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

@@ -8,14 +8,13 @@ using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;
 using SixLabors.Memory;
 
-// TODO: Consider pooling the TPixel palette also. For Rgba48+ this would end up on th LOH if 256 colors.
 namespace SixLabors.ImageSharp.Processing.Processors.Quantization
 {
     /// <summary>
     /// 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> : IDisposable
+    public class QuantizedFrame<TPixel> : IQuantizedFrame<TPixel>
         where TPixel : struct, IPixel<TPixel>
     {
         private IMemoryOwner<byte> pixels;
@@ -60,15 +59,6 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
         [MethodImpl(InliningOptions.ShortMethod)]
         public ReadOnlySpan<byte> GetPixelSpan() => this.pixels.GetSpan();
 
-        /// <summary>
-        /// Gets the representation of the pixels as a <see cref="Span{T}"/> of contiguous memory
-        /// at row <paramref name="rowIndex"/> beginning from the the first pixel on that row.
-        /// </summary>
-        /// <param name="rowIndex">The row.</param>
-        /// <returns>The <see cref="Span{T}"/></returns>
-        [MethodImpl(InliningOptions.ShortMethod)]
-        public ReadOnlySpan<byte> GetRowSpan(int rowIndex) => this.GetPixelSpan().Slice(rowIndex * this.Width, this.Width);
-
         /// <inheritdoc/>
         public void Dispose()
         {

tests/ImageSharp.Tests/Quantization/QuantizedImageTests.cs

@@ -49,7 +49,7 @@ namespace SixLabors.ImageSharp.Tests
 
                 foreach (ImageFrame<TPixel> frame in image.Frames)
                 {
-                    QuantizedFrame<TPixel> quantized =
+                    IQuantizedFrame<TPixel> quantized =
                         quantizer.CreateFrameQuantizer<TPixel>(this.Configuration).QuantizeFrame(frame);
 
                     int index = this.GetTransparentIndex(quantized);
@@ -72,7 +72,7 @@ namespace SixLabors.ImageSharp.Tests
 
                 foreach (ImageFrame<TPixel> frame in image.Frames)
                 {
-                    QuantizedFrame<TPixel> quantized =
+                    IQuantizedFrame<TPixel> quantized =
                         quantizer.CreateFrameQuantizer<TPixel>(this.Configuration).QuantizeFrame(frame);
 
                     int index = this.GetTransparentIndex(quantized);
@@ -81,7 +81,7 @@ namespace SixLabors.ImageSharp.Tests
             }
         }
 
-        private int GetTransparentIndex<TPixel>(QuantizedFrame<TPixel> quantized)
+        private int GetTransparentIndex<TPixel>(IQuantizedFrame<TPixel> quantized)
             where TPixel : struct, IPixel<TPixel>
         {
             // Transparent pixels are much more likely to be found at the end of a palette

tests/ImageSharp.Tests/Quantization/WuQuantizerTests.cs

@@ -15,7 +15,7 @@ namespace SixLabors.ImageSharp.Tests.Quantization
             var quantizer = new WuQuantizer(false);
 
             using (var image = new Image<Rgba32>(config, 1, 1, Rgba32.Black))
-            using (QuantizedFrame<Rgba32> result = quantizer.CreateFrameQuantizer<Rgba32>(config).QuantizeFrame(image.Frames[0]))
+            using (IQuantizedFrame<Rgba32> result = quantizer.CreateFrameQuantizer<Rgba32>(config).QuantizeFrame(image.Frames[0]))
             {
                 Assert.Equal(1, result.Palette.Length);
                 Assert.Equal(1, result.GetPixelSpan().Length);
@@ -32,7 +32,7 @@ namespace SixLabors.ImageSharp.Tests.Quantization
             var quantizer = new WuQuantizer(false);
 
             using (var image = new Image<Rgba32>(config, 1, 1, default(Rgba32)))
-            using (QuantizedFrame<Rgba32> result = quantizer.CreateFrameQuantizer<Rgba32>(config).QuantizeFrame(image.Frames[0]))
+            using (IQuantizedFrame<Rgba32> result = quantizer.CreateFrameQuantizer<Rgba32>(config).QuantizeFrame(image.Frames[0]))
             {
                 Assert.Equal(1, result.Palette.Length);
                 Assert.Equal(1, result.GetPixelSpan().Length);
@@ -75,7 +75,7 @@ namespace SixLabors.ImageSharp.Tests.Quantization
                 Configuration config = Configuration.Default;
                 var quantizer = new WuQuantizer(false);
                 using (IFrameQuantizer<Rgba32> frameQuantizer = quantizer.CreateFrameQuantizer<Rgba32>(config))
-                using (QuantizedFrame<Rgba32> result = frameQuantizer.QuantizeFrame(image.Frames[0]))
+                using (IQuantizedFrame<Rgba32> result = frameQuantizer.QuantizeFrame(image.Frames[0]))
                 {
                     Assert.Equal(256, result.Palette.Length);
                     Assert.Equal(256, result.GetPixelSpan().Length);
@@ -113,7 +113,7 @@ namespace SixLabors.ImageSharp.Tests.Quantization
                 Configuration config = Configuration.Default;
                 var quantizer = new WuQuantizer(false);
                 using (IFrameQuantizer<TPixel> frameQuantizer = quantizer.CreateFrameQuantizer<TPixel>(config))
-                using (QuantizedFrame<TPixel> result = frameQuantizer.QuantizeFrame(image.Frames[0]))
+                using (IQuantizedFrame<TPixel> result = frameQuantizer.QuantizeFrame(image.Frames[0]))
                 {
                     Assert.Equal(48, result.Palette.Length);
                 }
@@ -142,7 +142,7 @@ namespace SixLabors.ImageSharp.Tests.Quantization
                 var quantizer = new WuQuantizer(false);
 
                 using (IFrameQuantizer<Rgba32> frameQuantizer = quantizer.CreateFrameQuantizer<Rgba32>(config))
-                using (QuantizedFrame<Rgba32> result = frameQuantizer.QuantizeFrame(image.Frames[0]))
+                using (IQuantizedFrame<Rgba32> result = frameQuantizer.QuantizeFrame(image.Frames[0]))
                 {
                     Assert.Equal(4 * 8, result.Palette.Length);
                     Assert.Equal(256, result.GetPixelSpan().Length);