mirror of https://github.com/SixLabors/ImageSharp
Brian Popow
5 years ago
10 changed files with 212 additions and 34 deletions
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// Copyright (c) Six Labors.
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// Licensed under the Apache License, Version 2.0.
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using System; |
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using System.Runtime.CompilerServices; |
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using SixLabors.ImageSharp.Memory; |
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using SixLabors.ImageSharp.PixelFormats; |
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namespace SixLabors.ImageSharp.Formats.Tiff.PhotometricInterpretation |
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{ |
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internal class YCbCrTiffColor<TPixel> : TiffBaseColorDecoder<TPixel> |
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where TPixel : unmanaged, IPixel<TPixel> |
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{ |
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private readonly CodingRangeExpander yExpander; |
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private readonly CodingRangeExpander cbExpander; |
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private readonly CodingRangeExpander crExpander; |
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private readonly YCbCrToRgbConverter converter; |
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private static readonly Rational[] DefaultLuma = |
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{ |
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new Rational(299, 1000), |
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new Rational(587, 1000), |
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new Rational(114, 1000) |
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}; |
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private static readonly Rational[] DefaultReferenceBlackWhite = |
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{ |
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new Rational(0, 1), new Rational(255, 1), |
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new Rational(128, 1), new Rational(255, 1), |
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new Rational(128, 1), new Rational(255, 1) |
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}; |
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public YCbCrTiffColor(Rational[] referenceBlackAndWhite, Rational[] coefficients) |
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{ |
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referenceBlackAndWhite ??= DefaultReferenceBlackWhite; |
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coefficients ??= DefaultLuma; |
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if (referenceBlackAndWhite.Length != 6) |
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{ |
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TiffThrowHelper.ThrowImageFormatException("reference black and white array should have 6 entry's"); |
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} |
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if (coefficients.Length != 3) |
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{ |
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TiffThrowHelper.ThrowImageFormatException("luma coefficients array should have 6 entry's"); |
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} |
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this.yExpander = new CodingRangeExpander(referenceBlackAndWhite[0], referenceBlackAndWhite[1], 255); |
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this.cbExpander = new CodingRangeExpander(referenceBlackAndWhite[2], referenceBlackAndWhite[3], 127); |
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this.crExpander = new CodingRangeExpander(referenceBlackAndWhite[4], referenceBlackAndWhite[5], 127); |
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this.converter = new YCbCrToRgbConverter(coefficients[0], coefficients[1], coefficients[2]); |
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} |
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/// <inheritdoc/>
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public override void Decode(ReadOnlySpan<byte> data, Buffer2D<TPixel> pixels, int left, int top, int width, int height) |
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{ |
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var color = default(TPixel); |
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int offset = 0; |
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for (int y = top; y < top + height; y++) |
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{ |
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Span<TPixel> pixelRow = pixels.GetRowSpan(y).Slice(left, width); |
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for (int x = 0; x < pixelRow.Length; x++) |
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{ |
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Rgba32 rgba = this.ConvertToRgba32(data[offset], data[offset + 1], data[offset + 2]); |
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color.FromRgba32(rgba); |
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pixelRow[x] = color; |
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offset += 3; |
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} |
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} |
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} |
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[MethodImpl(MethodImplOptions.AggressiveInlining)] |
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private Rgba32 ConvertToRgba32(byte y, byte cb, byte cr) |
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{ |
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float yExpanded = this.yExpander.Expand(y); |
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float cbExpanded = this.cbExpander.Expand(cb); |
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float crExpanded = this.crExpander.Expand(cr); |
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Rgba32 rgba = this.converter.Convert(yExpanded, cbExpanded, crExpanded); |
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return rgba; |
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} |
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[MethodImpl(MethodImplOptions.AggressiveInlining)] |
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public static byte RoundAndClampTo8Bit(float value) |
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{ |
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int input = (int)MathF.Round(value); |
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return (byte)Math.Min(Math.Max(input, 0), 255); |
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} |
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private readonly struct CodingRangeExpander |
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{ |
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private readonly float f1; |
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private readonly float f2; |
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public CodingRangeExpander(Rational referenceBlack, Rational referenceWhite, int codingRange) |
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{ |
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float black = referenceBlack.ToSingle(); |
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float white = referenceWhite.ToSingle(); |
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this.f1 = codingRange / (white - black); |
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this.f2 = this.f1 * black; |
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} |
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[MethodImpl(MethodImplOptions.AggressiveInlining)] |
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public float Expand(float code) => (code * this.f1) - this.f2; |
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} |
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private readonly struct YCbCrToRgbConverter |
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{ |
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private readonly float cr2R; |
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private readonly float cb2B; |
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private readonly float y2G; |
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private readonly float cr2G; |
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private readonly float cb2G; |
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public YCbCrToRgbConverter(Rational lumaRed, Rational lumaGreen, Rational lumaBlue) |
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{ |
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this.cr2R = 2 - (2 * lumaRed.ToSingle()); |
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this.cb2B = 2 - (2 * lumaBlue.ToSingle()); |
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this.y2G = (1 - lumaBlue.ToSingle() - lumaRed.ToSingle()) / lumaGreen.ToSingle(); |
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this.cr2G = 2 * lumaRed.ToSingle() * (lumaRed.ToSingle() - 1) / lumaGreen.ToSingle(); |
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this.cb2G = 2 * lumaBlue.ToSingle() * (lumaBlue.ToSingle() - 1) / lumaGreen.ToSingle(); |
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} |
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[MethodImpl(MethodImplOptions.AggressiveInlining)] |
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public Rgba32 Convert(float y, float cb, float cr) |
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{ |
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var pixel = default(Rgba32); |
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pixel.R = RoundAndClampTo8Bit((cr * this.cr2R) + y); |
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pixel.G = RoundAndClampTo8Bit((this.y2G * y) + (this.cr2G * cr) + (this.cb2G * cb)); |
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pixel.B = RoundAndClampTo8Bit((cb * this.cb2B) + y); |
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pixel.A = byte.MaxValue; |
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return pixel; |
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} |
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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:dd1333eb93d8e7ea614b755ca1c8909c67b4b44fc03a8cab6be5491bf4d15841 |
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size 9753 |
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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 sha256:95f7b71c3a333734f799d73076032e31a6dfff1802bb3b454ba1eada7be50b0d |
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size 10058 |
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