mirror of https://github.com/SixLabors/ImageSharp
James Jackson-South
9 years ago
8 changed files with 935 additions and 204 deletions
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// <copyright file="JpegPixelArea.cs" company="James Jackson-South">
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// Copyright (c) James Jackson-South and contributors.
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// Licensed under the Apache License, Version 2.0.
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// </copyright>
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namespace ImageSharp.Formats.Jpeg.Port.Components |
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{ |
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using System; |
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using System.Diagnostics; |
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using System.Runtime.CompilerServices; |
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using ImageSharp.Memory; |
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/// <summary>
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/// Represents a section of the jpeg component data laid out in pixel order.
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/// </summary>
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internal struct JpegPixelArea : IDisposable |
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{ |
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private readonly int imageWidth; |
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private readonly int imageHeight; |
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private Buffer<byte> componentData; |
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private int rowStride; |
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/// <summary>
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/// Initializes a new instance of the <see cref="JpegPixelArea"/> struct.
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/// </summary>
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/// <param name="imageWidth">The image width</param>
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/// <param name="imageHeight">The image height</param>
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/// <param name="numberOfComponents">The number of components</param>
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public JpegPixelArea(int imageWidth, int imageHeight, int numberOfComponents) |
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{ |
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this.imageWidth = imageWidth; |
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this.imageHeight = imageHeight; |
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this.Width = 0; |
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this.Height = 0; |
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this.NumberOfComponents = numberOfComponents; |
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this.componentData = null; |
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this.rowStride = 0; |
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} |
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/// <summary>
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/// Gets the number of components
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/// </summary>
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public int NumberOfComponents { get; } |
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/// <summary>
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/// Gets the width
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/// </summary>
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public int Width { get; private set; } |
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/// <summary>
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/// Gets the height
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/// </summary>
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public int Height { get; private set; } |
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/// <summary>
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/// Organsizes the decoded jpeg components into a linear array ordered by component.
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/// This must be called before attempting to retrieve the data.
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/// </summary>
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/// <param name="components">The jpeg component blocks</param>
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/// <param name="width">The pixel area width</param>
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/// <param name="height">The pixel area height</param>
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public void LinearizeBlockData(ComponentBlocks components, int width, int height) |
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{ |
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this.Width = width; |
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this.Height = height; |
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int numberOfComponents = this.NumberOfComponents; |
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this.rowStride = width * numberOfComponents; |
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float scaleX = this.imageWidth / (float)width; |
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float scaleY = this.imageHeight / (float)height; |
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this.componentData = new Buffer<byte>(width * height * numberOfComponents); |
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const uint Mask3Lsb = 0xFFFFFFF8; // Used to clear the 3 LSBs
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using (var xScaleBlockOffset = new Buffer<int>(width)) |
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{ |
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for (int i = 0; i < numberOfComponents; i++) |
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{ |
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ref Component component = ref components.Components[i]; |
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float componentScaleX = component.ScaleX * scaleX; |
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float componentScaleY = component.ScaleY * scaleY; |
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int offset = i; |
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Buffer<short> output = component.Output; |
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int blocksPerScanline = (component.BlocksPerLine + 1) << 3; |
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// Precalculate the xScaleBlockOffset
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int j; |
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for (int x = 0; x < width; x++) |
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{ |
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j = 0 | (int)(x * componentScaleX); |
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xScaleBlockOffset[x] = (int)((j & Mask3Lsb) << 3) | (j & 7); |
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} |
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// Linearize the blocks of the component
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for (int y = 0; y < height; y++) |
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{ |
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j = 0 | (int)(y * componentScaleY); |
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int index = blocksPerScanline * (int)(j & Mask3Lsb) | ((j & 7) << 3); |
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for (int x = 0; x < width; x++) |
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{ |
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this.componentData[offset] = (byte)output[index + xScaleBlockOffset[x]]; |
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offset += numberOfComponents; |
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} |
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} |
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} |
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} |
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} |
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/// <summary>
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/// Gets a <see cref="Span{Byte}"/> representing the row 'y' beginning from the the first byte on that row.
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/// </summary>
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/// <param name="y">The y-coordinate of the pixel row. Must be greater than or equal to zero and less than the height of the pixel area.</param>
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/// <returns>The <see cref="Span{TPixel}"/></returns>
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[MethodImpl(MethodImplOptions.AggressiveInlining)] |
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public Span<byte> GetRowSpan(int y) |
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{ |
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this.CheckCoordinates(y); |
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return this.componentData.Slice(y * this.rowStride, this.rowStride); |
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} |
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/// <inheritdoc/>
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public void Dispose() |
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{ |
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this.componentData?.Dispose(); |
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this.componentData = null; |
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} |
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/// <summary>
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/// Checks the coordinates to ensure they are within bounds.
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/// </summary>
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/// <param name="y">The y-coordinate of the row. Must be greater than zero and less than the height of the area.</param>
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/// <exception cref="ArgumentOutOfRangeException">
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/// Thrown if the coordinates are not within the bounds of the image.
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/// </exception>
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[Conditional("DEBUG")] |
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private void CheckCoordinates(int y) |
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{ |
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if (y < 0 || y >= this.Height) |
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{ |
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throw new ArgumentOutOfRangeException(nameof(y), y, $"{y} is outwith the area bounds."); |
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} |
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} |
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} |
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} |
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@ -0,0 +1,128 @@ |
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namespace ImageSharp.Formats.Jpeg.Port.Components |
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{ |
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using System.Runtime.CompilerServices; |
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using ImageSharp.PixelFormats; |
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/// <summary>
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/// Provides 8-bit lookup tables for converting from YCbCr to Rgb colorspace.
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/// Methods to build the tables are based on libjpeg implementation.
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/// </summary>
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internal struct YCbCrToRgbTables |
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{ |
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/// <summary>
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/// The red red-chrominance table
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/// </summary>
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public static int[] CrRTable = new int[256]; |
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/// <summary>
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/// The blue blue-chrominance table
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/// </summary>
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public static int[] CbBTable = new int[256]; |
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/// <summary>
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/// The green red-chrominance table
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/// </summary>
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public static int[] CrGTable = new int[256]; |
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/// <summary>
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/// The green blue-chrominance table
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/// </summary>
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public static int[] CbGTable = new int[256]; |
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// Speediest right-shift on some machines and gives us enough accuracy at 4 decimal places.
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private const int ScaleBits = 16; |
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private const int Half = 1 << (ScaleBits - 1); |
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private const int MinSample = 0; |
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private const int HalfSample = 128; |
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private const int MaxSample = 255; |
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/// <summary>
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/// Initializes the YCbCr tables
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/// </summary>
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public static void Create() |
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{ |
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for (int i = 0, x = -128; i <= 255; i++, x++) |
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{ |
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// i is the actual input pixel value, in the range 0..255
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// The Cb or Cr value we are thinking of is x = i - 128
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// Cr=>R value is nearest int to 1.402 * x
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CrRTable[i] = RightShift((Fix(1.402F) * x) + Half); |
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// Cb=>B value is nearest int to 1.772 * x
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CbBTable[i] = RightShift((Fix(1.772F) * x) + Half); |
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// Cr=>G value is scaled-up -0.714136286
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CrGTable[i] = (-Fix(0.714136286F)) * x; |
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// Cb => G value is scaled - up - 0.344136286 * x
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// We also add in Half so that need not do it in inner loop
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CbGTable[i] = ((-Fix(0.344136286F)) * x) + Half; |
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} |
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} |
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/// <summary>
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/// Optimized method to pack bytes to the image from the YCbCr color space.
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/// </summary>
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/// <typeparam name="TPixel">The pixel format.</typeparam>
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/// <param name="packed">The packed pixel.</param>
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/// <param name="y">The y luminance component.</param>
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/// <param name="cb">The cb chroma component.</param>
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/// <param name="cr">The cr chroma component.</param>
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[MethodImpl(MethodImplOptions.AggressiveInlining)] |
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public static void PackYCbCr<TPixel>(ref TPixel packed, byte y, byte cb, byte cr) |
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where TPixel : struct, IPixel<TPixel> |
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{ |
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byte r = (byte)(y + CrRTable[cr]).Clamp(0, 255); |
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// The values for the G calculation are left scaled up, since we must add them together before rounding.
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byte g = (byte)(y + RightShift(CbGTable[cb] + CrGTable[cr])).Clamp(0, 255); |
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byte b = (byte)(y + CbBTable[cb]).Clamp(0, 255); |
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packed.PackFromRgba32(new Rgba32(r, g, b, 255)); |
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} |
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/// <summary>
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/// Optimized method to pack bytes to the image from the YccK color space.
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/// </summary>
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/// <typeparam name="TPixel">The pixel format.</typeparam>
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/// <param name="packed">The packed pixel.</param>
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/// <param name="y">The y luminance component.</param>
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/// <param name="cb">The cb chroma component.</param>
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/// <param name="cr">The cr chroma component.</param>
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/// <param name="k">The keyline component.</param>
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[MethodImpl(MethodImplOptions.AggressiveInlining)] |
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public static void PackYccK<TPixel>(ref TPixel packed, byte y, byte cb, byte cr, byte k) |
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where TPixel : struct, IPixel<TPixel> |
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{ |
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int c = (MaxSample - (y + CrRTable[cr])).Clamp(0, 255); |
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// The values for the G calculation are left scaled up, since we must add them together before rounding.
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int m = (MaxSample - (y + RightShift(CbGTable[cb] + CrGTable[cr]))).Clamp(0, 255); |
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int cy = (MaxSample - (y + CbBTable[cb])).Clamp(0, 255); |
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byte r = (byte)((c * k) / MaxSample); |
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byte g = (byte)((m * k) / MaxSample); |
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byte b = (byte)((cy * k) / MaxSample); |
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packed.PackFromRgba32(new Rgba32(r, g, b, MaxSample)); |
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} |
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[MethodImpl(MethodImplOptions.AggressiveInlining)] |
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private static int Fix(float x) |
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{ |
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return (int)((x * (1L << ScaleBits)) + 0.5F); |
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} |
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[MethodImpl(MethodImplOptions.AggressiveInlining)] |
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private static int RightShift(int x) |
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{ |
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return x >> ScaleBits; |
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} |
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} |
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} |
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@ -0,0 +1,3 @@ |
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version https://git-lfs.github.com/spec/v1 |
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oid sha256:33e3546a64df7fa1d528441926421b193e399a83490a6307762fb7eee9640bf0 |
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size 611572 |
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