From 4b8a5dc5c1b815f812e9e042d99b95aa367d3ba2 Mon Sep 17 00:00:00 2001 From: James Jackson-South Date: Wed, 26 Apr 2017 15:31:05 +1000 Subject: [PATCH] Use same conversion methods as libjpeg --- .../Components/Decoder/YCbCrToRgbTables.cs | 95 ++++++++++++++++ .../Components/Encoder/RgbToYCbCrTables.cs | 106 ++++++++++++++++++ .../Formats/Jpeg/JpegDecoderCore.cs | 37 +----- .../Formats/Jpeg/JpegEncoderCore.cs | 29 +---- 4 files changed, 213 insertions(+), 54 deletions(-) create mode 100644 src/ImageSharp/Formats/Jpeg/Components/Decoder/YCbCrToRgbTables.cs create mode 100644 src/ImageSharp/Formats/Jpeg/Components/Encoder/RgbToYCbCrTables.cs diff --git a/src/ImageSharp/Formats/Jpeg/Components/Decoder/YCbCrToRgbTables.cs b/src/ImageSharp/Formats/Jpeg/Components/Decoder/YCbCrToRgbTables.cs new file mode 100644 index 000000000..4195a3467 --- /dev/null +++ b/src/ImageSharp/Formats/Jpeg/Components/Decoder/YCbCrToRgbTables.cs @@ -0,0 +1,95 @@ +// +// Copyright (c) James Jackson-South and contributors. +// Licensed under the Apache License, Version 2.0. +// + +namespace ImageSharp.Formats.Jpg +{ + using System.Runtime.CompilerServices; + + using ImageSharp.PixelFormats; + + /// + /// Provides 8-bit lookup tables for converting from YCbCr to Rgb colorspace. + /// Methods to build the tables are based on libjpeg implementation. + /// + internal struct YCbCrToRgbTables + { + // Speediest right-shift on some machines and gives us enough accuracy at 4 decimal places. + private const int ScaleBits = 16; + + private const int Half = 1 << (ScaleBits - 1); + + private static readonly int[] CrRTable = new int[256]; + + private static readonly int[] CbBTable = new int[256]; + + private static readonly int[] CrGTable = new int[256]; + + private static readonly int[] CbGTable = new int[256]; + + /// + /// Optimized method to pack bytes to the image from the YCbCr color space. + /// + /// The pixel format. + /// The packed pixel. + /// The y luminance component. + /// The cb chroma component. + /// The cr chroma component. + [MethodImpl(MethodImplOptions.AggressiveInlining)] + public void Pack(ref TPixel packed, byte y, byte cb, byte cr) + where TPixel : struct, IPixel + { + // float r = MathF.Round(y + (1.402F * cr), MidpointRounding.AwayFromZero); + byte r = (byte)(y + CrRTable[cr]).Clamp(0, 255); + + // float g = MathF.Round(y - (0.344136F * cb) - (0.714136F * cr), MidpointRounding.AwayFromZero); + // The values for the G calculation are left scaled up, since we must add them together before rounding. + byte g = (byte)(y + RightShift(CbGTable[cb] + CrGTable[cr])).Clamp(0, 255); + + // float b = MathF.Round(y + (1.772F * cb), MidpointRounding.AwayFromZero); + byte b = (byte)(y + CbBTable[cb]).Clamp(0, 255); + + packed.PackFromBytes(r, g, b, byte.MaxValue); + } + + /// + /// Initializes the YCbCr tables + /// + /// The intialized + public YCbCrToRgbTables Init() + { + for (int i = 0, x = -128; i <= 255; i++, x++) + { + // i is the actual input pixel value, in the range 0..255 + // The Cb or Cr value we are thinking of is x = i - 128 + // Cr=>R value is nearest int to 1.402 * x + CrRTable[i] = RightShift((Fix(1.402F) * x) + Half); + + // Cb=>B value is nearest int to 1.772 * x + CbBTable[i] = RightShift((Fix(1.772F) * x) + Half); + + // Cr=>G value is scaled-up -0.714136286 + CrGTable[i] = (-Fix(0.714136286F)) * x; + + // Cb => G value is scaled - up - 0.344136286 * x + // We also add in Half so that need not do it in inner loop + CbGTable[i] = ((-Fix(0.344136286F)) * x) + Half; + } + + return this; + } + + [MethodImpl(MethodImplOptions.AggressiveInlining)] + private static int Fix(float x) + { + return (int)((x * (1L << ScaleBits)) + 0.5F); + } + + [MethodImpl(MethodImplOptions.AggressiveInlining)] + private static int RightShift(int x) + { + return x >> ScaleBits; + } + } +} \ No newline at end of file diff --git a/src/ImageSharp/Formats/Jpeg/Components/Encoder/RgbToYCbCrTables.cs b/src/ImageSharp/Formats/Jpeg/Components/Encoder/RgbToYCbCrTables.cs new file mode 100644 index 000000000..55a61011c --- /dev/null +++ b/src/ImageSharp/Formats/Jpeg/Components/Encoder/RgbToYCbCrTables.cs @@ -0,0 +1,106 @@ +// +// Copyright (c) James Jackson-South and contributors. +// Licensed under the Apache License, Version 2.0. +// + +namespace ImageSharp.Formats.Jpg +{ + using System.Runtime.CompilerServices; + + /// + /// Provides 8-bit lookup tables for converting from Rgb to YCbCr colorspace. + /// Methods to build the tables are based on libjpeg implementation. + /// + internal struct RgbToYCbCrTables + { + // Speediest right-shift on some machines and gives us enough accuracy at 4 decimal places. + private const int ScaleBits = 16; + + private const int GYOffset = 256; + + private const int BYOffset = 2 * 256; + + private const int RCbOffset = 3 * 256; + + private const int GCbOffset = 4 * 256; + + private const int BCbOffset = 5 * 256; + + // B=>Cb and R=>Cr are the same + private const int RCrOffset = BCbOffset; + + private const int GCrOffset = 6 * 256; + + private const int BCrOffset = 7 * 256; + + private const int CBCrOffset = 128 << ScaleBits; + + private const int Half = 1 << (ScaleBits - 1); + + private static readonly int[] YCbCrTable = new int[8 * 256]; + + /// + /// Optimized method to allocates the correct y, cb, and cr values to the DCT blocks from the given r, g, b values. + /// + /// The The luminance block. + /// The red chroma block. + /// The blue chroma block. + /// The current index. + /// The red value. + /// The green value. + /// The blue value. + [MethodImpl(MethodImplOptions.AggressiveInlining)] + public unsafe void Allocate(ref float* yBlockRaw, ref float* cbBlockRaw, ref float* crBlockRaw, int index, int r, int g, int b) + { + // float y = (0.299F * r) + (0.587F * g) + (0.114F * b); + yBlockRaw[index] = (YCbCrTable[r] + YCbCrTable[g + GYOffset] + YCbCrTable[b + BYOffset]) >> ScaleBits; + + // float cb = 128F + ((-0.168736F * r) - (0.331264F * g) + (0.5F * b)); + cbBlockRaw[index] = (YCbCrTable[r + RCbOffset] + YCbCrTable[g + GCbOffset] + YCbCrTable[b + BCbOffset]) >> ScaleBits; + + // float b = MathF.Round(y + (1.772F * cb), MidpointRounding.AwayFromZero); + crBlockRaw[index] = (YCbCrTable[r + RCrOffset] + YCbCrTable[g + GCrOffset] + YCbCrTable[b + BCrOffset]) >> ScaleBits; + } + + /// + /// Initializes the YCbCr tables + /// + /// The intialized + public RgbToYCbCrTables Init() + { + for (int i = 0; i <= 255; i++) + { + // The values for the calculations are left scaled up since we must add them together before rounding. + YCbCrTable[i] = Fix(0.299F) * i; + YCbCrTable[i + GYOffset] = Fix(0.587F) * i; + YCbCrTable[i + BYOffset] = (Fix(0.114F) * i) + Half; + YCbCrTable[i + RCbOffset] = (-Fix(0.168735892F)) * i; + YCbCrTable[i + GCbOffset] = (-Fix(0.331264108F)) * i; + + // We use a rounding fudge - factor of 0.5 - epsilon for Cb and Cr. + // This ensures that the maximum output will round to 255 + // not 256, and thus that we don't have to range-limit. + // + // B=>Cb and R=>Cr tables are the same + YCbCrTable[i + BCbOffset] = (Fix(0.5F) * i) + CBCrOffset + Half - 1; + + YCbCrTable[i + GCrOffset] = (-Fix(0.418687589F)) * i; + YCbCrTable[i + BCrOffset] = (-Fix(0.081312411F)) * i; + } + + return this; + } + + [MethodImpl(MethodImplOptions.AggressiveInlining)] + private static int Fix(float x) + { + return (int)((x * (1L << ScaleBits)) + 0.5F); + } + + [MethodImpl(MethodImplOptions.AggressiveInlining)] + private static int RightShift(int x) + { + return x >> ScaleBits; + } + } +} \ No newline at end of file diff --git a/src/ImageSharp/Formats/Jpeg/JpegDecoderCore.cs b/src/ImageSharp/Formats/Jpeg/JpegDecoderCore.cs index 186c1e528..3faffb566 100644 --- a/src/ImageSharp/Formats/Jpeg/JpegDecoderCore.cs +++ b/src/ImageSharp/Formats/Jpeg/JpegDecoderCore.cs @@ -7,7 +7,6 @@ namespace ImageSharp.Formats { using System; using System.IO; - using System.Runtime.CompilerServices; using System.Threading.Tasks; using ImageSharp.Formats.Jpg; @@ -38,6 +37,11 @@ namespace ImageSharp.Formats public InputProcessor InputProcessor; #pragma warning restore SA401 + /// + /// Lookup tables for converting YCbCr to Rgb + /// + private static readonly YCbCrToRgbTables YCbCrToRgbTables = default(YCbCrToRgbTables).Init(); + /// /// The decoder options. /// @@ -251,35 +255,6 @@ namespace ImageSharp.Formats } } - /// - /// Optimized method to pack bytes to the image from the YCbCr color space. - /// This is faster than implicit casting as it avoids double packing. - /// - /// The pixel format. - /// The packed pixel. - /// The y luminance component. - /// The cb chroma component. - /// The cr chroma component. - [MethodImpl(MethodImplOptions.AggressiveInlining)] - private static void PackYcbCr(ref TPixel packed, byte y, byte cb, byte cr) - where TPixel : struct, IPixel - { - int ccb = cb - 128; - int ccr = cr - 128; - - // Speed up the algorithm by removing floating point calculation - // Scale by 65536, add .5F and truncate value. We use bit shifting to divide the result - int r0 = 91881 * ccr; // (1.402F * 65536) + .5F - int g0 = 22554 * ccb; // (0.34414F * 65536) + .5F - int g1 = 46802 * ccr; // (0.71414F * 65536) + .5F - int b0 = 116130 * ccb; // (1.772F * 65536) + .5F - - byte r = (byte)(y + (r0 >> 16)).Clamp(0, 255); - byte g = (byte)(y - (g0 >> 16) - (g1 >> 16)).Clamp(0, 255); - byte b = (byte)(y + (b0 >> 16)).Clamp(0, 255); - packed.PackFromBytes(r, g, b, 255); - } - /// /// Read metadata from stream and read the blocks in the scans into . /// @@ -721,7 +696,7 @@ namespace ImageSharp.Formats byte cr = this.ycbcrImage.CrChannel.Pixels[co + (x / scale)]; TPixel packed = default(TPixel); - PackYcbCr(ref packed, yy, cb, cr); + YCbCrToRgbTables.Pack(ref packed, yy, cb, cr); pixels[x, y] = packed; } }); diff --git a/src/ImageSharp/Formats/Jpeg/JpegEncoderCore.cs b/src/ImageSharp/Formats/Jpeg/JpegEncoderCore.cs index eb083c35d..b741fb2e6 100644 --- a/src/ImageSharp/Formats/Jpeg/JpegEncoderCore.cs +++ b/src/ImageSharp/Formats/Jpeg/JpegEncoderCore.cs @@ -5,11 +5,9 @@ namespace ImageSharp.Formats { - using System; using System.Buffers; using System.IO; using System.Runtime.CompilerServices; - using ImageSharp.Formats.Jpg; using ImageSharp.Formats.Jpg.Components; using ImageSharp.PixelFormats; @@ -24,6 +22,11 @@ namespace ImageSharp.Formats /// private const int QuantizationTableCount = 2; + /// + /// Lookup tables for converting Rgb to YCbCr + /// + private static readonly RgbToYCbCrTables RgbToYCbCrTables = default(RgbToYCbCrTables).Init(); + /// /// Counts the number of bits needed to hold an integer. /// @@ -321,29 +324,9 @@ namespace ImageSharp.Formats int g = Unsafe.Add(ref data0, dataIdx + 1); int b = Unsafe.Add(ref data0, dataIdx + 2); - // Speed up the algorithm by removing floating point calculation - // Scale by 65536, add .5F and truncate value. We use bit shifting to divide the result - int y0 = 19595 * r; // (0.299F * 65536) + .5F - int y1 = 38470 * g; // (0.587F * 65536) + .5F - int y2 = 7471 * b; // (0.114F * 65536) + .5F - - int cb0 = -11057 * r; // (-0.168736F * 65536) + .5F - int cb1 = 21710 * g; // (0.331264F * 65536) + .5F - int cb2 = 32768 * b; // (0.5F * 65536) + .5F - - int cr0 = 32768 * r; // (0.5F * 65536) + .5F - int cr1 = 27439 * g; // (0.418688F * 65536) + .5F - int cr2 = 5329 * b; // (0.081312F * 65536) + .5F - - float yy = (y0 + y1 + y2) >> 16; - float cb = 128 + ((cb0 - cb1 + cb2) >> 16); - float cr = 128 + ((cr0 - cr1 - cr2) >> 16); - int index = j8 + i; - yBlockRaw[index] = yy; - cbBlockRaw[index] = cb; - crBlockRaw[index] = cr; + RgbToYCbCrTables.Allocate(ref yBlockRaw, ref cbBlockRaw, ref crBlockRaw, index, r, g, b); dataIdx += 3; }