JpegColorConverter

src/ImageSharp/Formats/Jpeg/Common/Decoder/JpegColorConverter.FromYCbCr.cs

@@ -0,0 +1,47 @@
+using System;
+using System.Numerics;
+using System.Runtime.CompilerServices;
+
+using SixLabors.ImageSharp.ColorSpaces;
+using SixLabors.ImageSharp.ColorSpaces.Conversion.Implementation.YCbCrColorSapce;
+
+namespace SixLabors.ImageSharp.Formats.Jpeg.Common.Decoder
+{
+    internal abstract partial class JpegColorConverter
+    {
+        private class FromYCbCr : JpegColorConverter
+        {
+            private static readonly YCbCrAndRgbConverter Converter = new YCbCrAndRgbConverter();
+
+            public FromYCbCr()
+                : base(JpegColorSpace.YCbCr)
+            {
+            }
+
+            public override void ConvertToRGBA(ComponentValues values, Span<Vector4> result)
+            {
+                // TODO: We can optimize a lot here with Vector<float> and SRCS.Unsafe()!
+                ReadOnlySpan<float> yVals = values.Component0;
+                ReadOnlySpan<float> cbVals = values.Component1;
+                ReadOnlySpan<float> crVals = values.Component2;
+
+                Vector4 rgbaVector = new Vector4(0, 0, 0, 1);
+
+                for (int i = 0; i < result.Length; i++)
+                {
+                    float colY = yVals[i];
+                    float colCb = cbVals[i];
+                    float colCr = crVals[i];
+
+                    YCbCr yCbCr = new YCbCr(colY, colCb, colCr);
+
+                    // Slow conversion for now:
+                    Rgb rgb = Converter.Convert(yCbCr);
+
+                    Unsafe.As<Vector4, Vector3>(ref rgbaVector) = rgb.Vector;
+                    result[i] = rgbaVector;
+                }
+            }
+        }
+    }
+}

src/ImageSharp/Formats/Jpeg/Common/Decoder/JpegColorConverter.cs

@@ -0,0 +1,70 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Numerics;
+
+using SixLabors.ImageSharp.Memory;
+
+namespace SixLabors.ImageSharp.Formats.Jpeg.Common.Decoder
+{
+    internal abstract partial class JpegColorConverter
+    {
+        private static readonly JpegColorConverter[] Converters = { new FromYCbCr(), };
+
+        protected JpegColorConverter(JpegColorSpace colorSpace)
+        {
+            this.ColorSpace = colorSpace;
+        }
+
+        public JpegColorSpace ColorSpace { get; }
+
+        public static JpegColorConverter GetConverter(JpegColorSpace colorSpace)
+        {
+            JpegColorConverter converter = Converters.FirstOrDefault(c => c.ColorSpace == colorSpace);
+            if (converter == null)
+            {
+                throw new Exception($"Could not find any converter for JpegColorSpace {colorSpace}!");
+            }
+
+            return converter;
+        }
+
+        public abstract void ConvertToRGBA(ComponentValues values, Span<Vector4> result);
+
+        public struct ComponentValues
+        {
+            public readonly int ComponentCount;
+
+            public readonly ReadOnlySpan<float> Component0;
+
+            public readonly ReadOnlySpan<float> Component1;
+
+            public readonly ReadOnlySpan<float> Component2;
+
+            public readonly ReadOnlySpan<float> Component3;
+
+            public ComponentValues(IReadOnlyList<IBuffer2D<float>> componentBuffers, int row)
+            {
+                this.ComponentCount = componentBuffers.Count;
+
+                this.Component0 = componentBuffers[0].GetRowSpan(row);
+                this.Component1 = Span<float>.Empty;
+                this.Component2 = Span<float>.Empty;
+                this.Component3 = Span<float>.Empty;
+
+                if (this.ComponentCount > 1)
+                {
+                    this.Component1 = componentBuffers[1].GetRowSpan(row);
+                    if (this.ComponentCount > 2)
+                    {
+                        this.Component2 = componentBuffers[2].GetRowSpan(row);
+                        if (this.ComponentCount > 3)
+                        {
+                            this.Component3 = componentBuffers[3].GetRowSpan(row);
+                        }
+                    }
+                }
+            }
+        }
+    }
+}

src/ImageSharp/Formats/Jpeg/Common/Decoder/JpegImagePostProcessor.cs

@@ -1,9 +1,11 @@
 using System;
+using System.Collections.Generic;
 using System.Linq;
 using System.Numerics;
 using System.Runtime.CompilerServices;
 using SixLabors.ImageSharp.ColorSpaces;
 using SixLabors.ImageSharp.ColorSpaces.Conversion.Implementation.YCbCrColorSapce;
+using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;
 using SixLabors.Primitives;
 
@@ -15,6 +17,10 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Common.Decoder
 
         public const int PixelRowsPerStep = 4 * 8;
 
+        private readonly Buffer<Vector4> rgbaBuffer;
+
+        private JpegColorConverter colorConverter;
+
         public JpegImagePostProcessor(IRawJpegData rawJpeg)
         {
             this.RawJpeg = rawJpeg;
@@ -23,6 +29,8 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Common.Decoder
             this.PostProcessorBufferSize = new Size(c0.SizeInBlocks.Width * 8, PixelRowsPerStep);
 
             this.ComponentProcessors = rawJpeg.Components.Select(c => new JpegComponentPostProcessor(this, c)).ToArray();
+            this.rgbaBuffer = new Buffer<Vector4>(rawJpeg.ImageSizeInPixels.Width);
+            this.colorConverter = JpegColorConverter.GetConverter(rawJpeg.ColorSpace);
         }
 
         public JpegComponentPostProcessor[] ComponentProcessors { get; }
@@ -41,6 +49,8 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Common.Decoder
             {
                 cpp.Dispose();
             }
+
+            this.rgbaBuffer.Dispose();
         }
 
         public bool DoPostProcessorStep<TPixel>(Image<TPixel> destination)
@@ -65,6 +75,11 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Common.Decoder
         public void PostProcess<TPixel>(Image<TPixel> destination)
             where TPixel : struct, IPixel<TPixel>
         {
+            if (this.RawJpeg.ImageSizeInPixels != destination.Size())
+            {
+                throw new ArgumentException("Input image is not of the size of the processed one!");
+            }
+
             while (this.DoPostProcessorStep(destination))
             {
             }
@@ -75,31 +90,18 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Common.Decoder
         {
             int maxY = Math.Min(destination.Height, this.CurrentImageRowInPixels + PixelRowsPerStep);
 
-            JpegComponentPostProcessor[] cp = this.ComponentProcessors;
-
-            YCbCrAndRgbConverter converter = new YCbCrAndRgbConverter(); 
-
-            Vector4 rgbaVector = new Vector4(0, 0, 0, 1);
+            Buffer2D<float>[] buffers = this.ComponentProcessors.Select(cp => cp.ColorBuffer).ToArray();
 
             for (int yy = this.CurrentImageRowInPixels; yy < maxY; yy++)
             {
                 int y = yy - this.CurrentImageRowInPixels;
 
-                Span<TPixel> destRow = destination.GetRowSpan(yy);
-
-                for (int x = 0; x < destination.Width; x++)
-                {
-                    float colY = cp[0].ColorBuffer[x, y];
-                    float colCb = cp[1].ColorBuffer[x, y];
-                    float colCr = cp[2].ColorBuffer[x, y];
-
-                    YCbCr yCbCr = new YCbCr(colY, colCb, colCr);
-                    Rgb rgb = converter.Convert(yCbCr);
+                var values = new JpegColorConverter.ComponentValues(buffers, y);
+                this.colorConverter.ConvertToRGBA(values, this.rgbaBuffer);
 
-                    Unsafe.As<Vector4, Vector3>(ref rgbaVector) = rgb.Vector;
+                Span<TPixel> destRow = destination.GetRowSpan(yy);
 
-                    destRow[x].PackFromVector4(rgbaVector);
-                }
+                PixelOperations<TPixel>.Instance.PackFromVector4(this.rgbaBuffer, destRow, destination.Width);
             }
         }
     }

src/ImageSharp/Memory/Buffer.cs

@@ -7,12 +7,13 @@ using System.Runtime.InteropServices;
 
 namespace SixLabors.ImageSharp.Memory
 {
+    /// <inheritdoc />
     /// <summary>
     /// Manages a buffer of value type objects as a Disposable resource.
     /// The backing array is either pooled or comes from the outside.
     /// </summary>
     /// <typeparam name="T">The value type.</typeparam>
-    internal class Buffer<T> : IDisposable
+    internal class Buffer<T> : IBuffer<T>
         where T : struct
     {
         /// <summary>
@@ -205,7 +206,8 @@ namespace SixLabors.ImageSharp.Memory
         {
             if (this.IsDisposedOrLostArrayOwnership)
             {
-                throw new InvalidOperationException("TakeArrayOwnership() is invalid: either Buffer<T> is disposed or TakeArrayOwnership() has been called multiple times!");
+                throw new InvalidOperationException(
+                    "TakeArrayOwnership() is invalid: either Buffer<T> is disposed or TakeArrayOwnership() has been called multiple times!");
             }
 
             this.IsDisposedOrLostArrayOwnership = true;

src/ImageSharp/Memory/IBuffer.cs

@@ -0,0 +1,18 @@
+using System;
+
+namespace SixLabors.ImageSharp.Memory
+{
+    /// <inheritdoc />
+    /// <summary>
+    /// Represents a contigous memory buffer of value-type items "promising" a <see cref="T:System.Span`1" />
+    /// </summary>
+    /// <typeparam name="T">The value type</typeparam>
+    internal interface IBuffer<T> : IDisposable
+        where T : struct
+    {
+        /// <summary>
+        /// Gets the span to the memory "promised" by this buffer
+        /// </summary>
+        Span<T> Span { get; }
+    }
+}

tests/ImageSharp.Tests/Formats/Jpg/JpegColorConverterTests.cs

@@ -0,0 +1,81 @@
+using System;
+using System.Numerics;
+
+using SixLabors.ImageSharp.ColorSpaces;
+using SixLabors.ImageSharp.ColorSpaces.Conversion;
+using SixLabors.ImageSharp.ColorSpaces.Conversion.Implementation.YCbCrColorSapce;
+using SixLabors.ImageSharp.Formats.Jpeg.Common.Decoder;
+using SixLabors.ImageSharp.Memory;
+using SixLabors.ImageSharp.Tests.Colorspaces;
+using SixLabors.ImageSharp.Tests.Formats.Jpg.Utils;
+
+using Xunit;
+using Xunit.Abstractions;
+
+namespace SixLabors.ImageSharp.Tests.Formats.Jpg
+{
+    public class JpegColorConverterTests
+    {
+        private const float Precision = 0.1f;
+
+        private const int InputBufferLength = 42;
+
+        // The result buffer could be shorter
+        private const int ResultBufferLength = 40;
+
+        private readonly Vector4[] Result = new Vector4[ResultBufferLength];
+
+        private static readonly ColorSpaceConverter ColorSpaceConverter = new ColorSpaceConverter();
+
+        public JpegColorConverterTests(ITestOutputHelper output)
+        {
+            this.Output = output;
+        }
+
+        private ITestOutputHelper Output { get; }
+
+        private static JpegColorConverter.ComponentValues CreateRandomValues(int componentCount, float maxVal = 255f)
+        {
+            var rnd = new Random(42);
+            Buffer2D<float>[] buffers = new Buffer2D<float>[componentCount];
+            for (int i = 0; i < componentCount; i++)
+            {    
+                float[] values = new float[InputBufferLength];
+
+                for (int j = 0; j < InputBufferLength; j++)
+                {
+                    values[j] = (float)rnd.NextDouble() * maxVal;
+                }
+
+                // no need to dispose when buffer is not array owner
+                buffers[i] = new Buffer2D<float>(values, values.Length, 1);
+            }
+            return new JpegColorConverter.ComponentValues(buffers, 0);
+        }
+
+        [Fact]
+        public void ConvertFromYCbCr()
+        {
+            var converter = JpegColorConverter.GetConverter(JpegColorSpace.YCbCr);
+
+            JpegColorConverter.ComponentValues values = CreateRandomValues(3);
+            
+            converter.ConvertToRGBA(values, this.Result);
+            
+            for (int i = 0; i < ResultBufferLength; i++)
+            {
+                float y = values.Component0[i];
+                float cb = values.Component1[i];
+                float cr = values.Component2[i];
+                YCbCr ycbcr = new YCbCr(y, cb, cr);
+
+                Vector4 rgba = this.Result[i];
+                Rgb actual = new Rgb(rgba.X, rgba.Y, rgba.Z);
+                Rgb expected = ColorSpaceConverter.ToRgb(ycbcr);
+                
+                Assert.True(actual.AlmostEquals(expected, Precision));
+                Assert.Equal(1, rgba.W);
+            }
+        }
+    }
+}