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Reference RGB-YUV conversions

pull/2633/head
Ynse Hoornenborg 2 years ago
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2 changed files with 314 additions and 5 deletions
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  1. 156
      tests/ImageSharp.Tests/Formats/Heif/Av1/Av1ReferenceYuvConverter.cs
  2. 163
      tests/ImageSharp.Tests/Formats/Heif/Av1/Av1YuvConverterTests.cs

156
tests/ImageSharp.Tests/Formats/Heif/Av1/Av1ReferenceYuvConverter.cs
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@ -0,0 +1,156 @@
// Copyright (c) Six Labors.
// Licensed under the Six Labors Split License.
using System.Numerics;
using SixLabors.ImageSharp.Formats.Heif.Av1;
using SixLabors.ImageSharp.PixelFormats;
namespace SixLabors.ImageSharp.Tests.Formats.Heif.Av1;
/// <summary>
/// This simulates converting 24-bit RGB values to YUV, then back to 24-bit RGB.
/// Using BT.709 transfer functions: https://en.wikipedia.org/wiki/Rec._709
///
/// It demonstrates that converting to 30-bit YUV then back to 24-bit RGB is lossy.
/// Using 10 bits per YUV value appears to be lossless.
///
/// Converting RGB (24-bit) -> YUV(64-bit floats per channel, normalized[0 - 1]) -> RGB(24-bit)
/// Found 0 inaccurate conversions out of 16581375 RGB values
///
/// Converting RGB(24-bit) -> YUV(30-bit) -> RGB(24-bit)
/// Found 0 inaccurate conversions out of 16581375 RGB values
///
/// Converting RGB(24-bit) -> YUV(24-bit) -> RGB(24-bit)
/// Found 4058422 accurate conversions out of 16581375 RGB values
/// Found 12522953 inaccurate conversions out of 16581375 RGB values
/// Off by: {1: 8786792, 2: 3727753, 3: 8408}
/// </summary>
/// <remarks> Ported from Python to C# from: https://gist.github.com/linrock/5be4f365c9c9e61eee9e8984ba13cb25.</remarks>
internal class Av1ReferenceYuvConverter
{
// The range of UV values in BT.709 is [-Umax, Umax] and [-Vmax, Vmax]
private const double Umax = 0.436;
private const double Vmax = 0.615;
// Constants used in BT.709
private const double Wr = 0.2126;
private const double Wb = 0.0722;
// Constants used in BT.601
// private const double Wr = 0.299;
// private const double Wb = 0.114;
private const double Wg = 1 - Wr - Wb;
public static Span<Rgb24> RgbToYuv(Span<Rgb24> row)
{
Rgb24[] result = new Rgb24[row.Length];
for (int i = 0; i < row.Length; i++)
{
double[] current = RgbToYuv(row[i], false, true, false);
byte y = (byte)current[0];
byte u = (byte)current[1];
byte v = (byte)current[2];
result[i] = new Rgb24(y, u, v);
}
return result;
}
public static double[] RgbToYuv(Rgb24 rgb, bool normalize = false, bool is_8bit = false, bool is_10bit = false)
{
double r = rgb.R / 255.0;
double g = rgb.G / 255.0;
double b = rgb.B / 255.0;
double y = (Wr * r) + (Wg * g) + (Wb * b);
double u = Umax * (b - y) / (1 - Wb);
double v = Vmax * (r - y) / (1 - Wr);
// y[0, 1] u[-Umax, Umax] v[-Vmax, Vmax]
if (normalize)
{
u = (u + Umax) / (2 * Umax);
v = (v + Vmax) / (2 * Vmax);
// y[0, 1] u[0, 1] v[0, 1]
}
if (is_8bit)
{
y = Math.Round(y * 255);
u = Math.Round(u * 255);
v = Math.Round(v * 255);
// y[0, 255] u[0, 255] v[0, 255]
}
if (is_10bit)
{
y = Math.Round(y * 1023);
u = Math.Round(u * 1023);
v = Math.Round(v * 1023);
// y[0, 1023] u[0, 1023] v[0, 1023]
}
return [y, u, v];
}
public static Span<Rgb24> YuvToRgb(Av1FrameBuffer<byte> frameBuffer)
{
Span<byte> yRow = frameBuffer.BufferY!.DangerousGetSingleSpan();
Span<byte> uRow = frameBuffer.BufferCb!.DangerousGetSingleSpan();
Span<byte> vRow = frameBuffer.BufferCr!.DangerousGetSingleSpan();
Rgb24[] result = new Rgb24[yRow.Length];
double[] yuv = new double[3];
for (int i = 0; i < yRow.Length; i++)
{
yuv[0] = yRow[i];
yuv[1] = uRow[i];
yuv[2] = vRow[i];
result[i] = YuvToRgb(yuv, false, true, false);
}
return result;
}
public static Rgb24 YuvToRgb(double[] yuv, bool normalized = false, bool is_8bit = false, bool is_10bit = false)
{
double y = yuv[0];
double u = yuv[1];
double v = yuv[2];
if (is_8bit)
{
// y[0, 255] u[0, 255] v[0, 255]
y /= 255.0;
u /= 255.0;
v /= 255.0;
}
if (is_10bit)
{
// y[0, 1023] u[0, 1023] v[0, 1023]
y /= 1023.0;
u /= 1023.0;
v /= 1023.0;
}
if (normalized)
{
// y [0, 1], u [0, 1], v[0, 1]
u = (u - 0.5) * 2 * Umax;
v = (v - 0.5) * 2 * Vmax;
// y [0, 1], u [-Umax, Umax], v[-Vmax, Vmax]
}
// r = y + 1.28033 * v
// g = y - 0.21482 * u - 0.38059 * v
// b = y + 2.12798 * u
double r = y + (v * (1 - Wr) / Vmax);
double g = y - (u * Wb * (1 - Wb) / (Umax * Wg)) - (v * Wr * (1 - Wr) / (Vmax * Wg));
double b = y + (u * (1 - Wb) / Umax);
return new Rgb24((byte)Math.Round(r * 255), (byte)Math.Round(g * 255), (byte)Math.Round(b * 255));
}
}

163
tests/ImageSharp.Tests/Formats/Heif/Av1/Av1YuvConverterTests.cs
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@ -1,12 +1,8 @@
// Copyright (c) Six Labors.
// Licensed under the Six Labors Split License.
using Iced.Intel;
using SixLabors.ImageSharp.Formats.Heif.Av1;
using SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
using SixLabors.ImageSharp.Formats.Heif.Av1.Pipeline;
using SixLabors.ImageSharp.Formats.Heif.Av1.Tiling;
using SixLabors.ImageSharp.Memory;
using SixLabors.ImageSharp.PixelFormats;
using SixLabors.ImageSharp.Tests.TestUtilities.ImageComparison;
@ -15,6 +11,163 @@ namespace SixLabors.ImageSharp.Tests.Formats.Heif.Av1;
[Trait("Format", "Avif")]
public class Av1YuvConverterTests
{
[Theory]
[InlineData(255, 255, 255, 255, 127, 127)]
[InlineData(0, 0, 0, 0, 127, 127)]
[InlineData(42, 42, 42, 42, 127, 127)]
[InlineData(150, 100, 50, 107, 97, 154)]
public void RgbToYuvSinglePixel(byte r, byte g, byte b, int y, int u, int v)
{
// Assign
using Image<Rgb24> image = new(1, 1);
ImageFrame<Rgb24> frame = image.Frames.RootFrame;
frame.DangerousTryGetSinglePixelMemory(out Memory<Rgb24> memory);
memory.Span[0] = new Rgb24(r, g, b);
ObuSequenceHeader sequenceHeader = new();
sequenceHeader.MaxFrameWidth = 1;
sequenceHeader.MaxFrameHeight = 1;
Av1FrameBuffer<byte> frameBuffer = new(Configuration.Default, sequenceHeader, Av1ColorFormat.Yuv444, false);
// Act
Av1YuvConverter.ConvertFromRgb(Configuration.Default, frame, frameBuffer);
// Assert
byte actualY = frameBuffer.BufferY.DangerousGetRowSpan(0)[0];
byte actualU = frameBuffer.BufferCb.DangerousGetRowSpan(0)[0];
byte actualV = frameBuffer.BufferCr.DangerousGetRowSpan(0)[0];
Assert.Equal(y, actualY);
Assert.Equal(u, actualU);
Assert.Equal(v, actualV);
}
[Theory]
[InlineData(255, 255, 255, 255, 127, 127)]
[InlineData(0, 0, 0, 0, 127, 127)]
[InlineData(42, 42, 42, 42, 127, 127)]
[InlineData(150, 100, 50, 107, 97, 154)]
public void YuvToRgbSinglePixel(byte r, byte g, byte b, int y, int u, int v)
{
// Assign
using Image<Rgb24> image = new(1, 1);
ImageFrame<Rgb24> frame = image.Frames.RootFrame;
ObuSequenceHeader sequenceHeader = new();
sequenceHeader.MaxFrameWidth = 1;
sequenceHeader.MaxFrameHeight = 1;
Av1FrameBuffer<byte> frameBuffer = new(Configuration.Default, sequenceHeader, Av1ColorFormat.Yuv444, false);
frameBuffer.BufferY.DangerousGetRowSpan(0)[0] = (byte)y;
frameBuffer.BufferCb.DangerousGetRowSpan(0)[0] = (byte)u;
frameBuffer.BufferCr.DangerousGetRowSpan(0)[0] = (byte)v;
// Act
Av1YuvConverter.ConvertToRgb(Configuration.Default, frameBuffer, frame);
// Assert
frame.DangerousTryGetSinglePixelMemory(out Memory<Rgb24> memory);
Rgb24 actual = memory.Span[0];
Assert.Equal(r, actual.R, 1d);
Assert.Equal(g, actual.G, 1d);
Assert.Equal(b, actual.B, 1d);
}
[Fact]
public void RgbToYuvCompareToReferenceRandomPixels()
{
const int sampleCount = 1000;
// Assign
using Image<Rgb24> image = new(sampleCount, 1);
ImageFrame<Rgb24> frame = image.Frames.RootFrame;
frame.DangerousTryGetSinglePixelMemory(out Memory<Rgb24> memory);
Random rnd = new(42);
Span<byte> input = new byte[sampleCount * 3];
CreateTestData(rnd, input);
PixelOperations<Rgb24>.Instance.FromBgr24Bytes(Configuration.Default, input, memory.Span, image.Width);
ObuSequenceHeader sequenceHeader = new();
sequenceHeader.MaxFrameWidth = image.Width;
sequenceHeader.MaxFrameHeight = image.Height;
Av1FrameBuffer<byte> frameBuffer = new(Configuration.Default, sequenceHeader, Av1ColorFormat.Yuv444, false);
// Act
Av1YuvConverter.ConvertFromRgb(Configuration.Default, frame, frameBuffer);
Span<Rgb24> referenceOutput = Av1ReferenceYuvConverter.RgbToYuv(memory.Span);
// Assert
Span<Rgb24> actual = new Rgb24[frameBuffer.Width];
Span<byte> yRow = frameBuffer.BufferY!.DangerousGetSingleSpan();
Span<byte> uRow = frameBuffer.BufferCb!.DangerousGetSingleSpan();
Span<byte> vRow = frameBuffer.BufferCr!.DangerousGetSingleSpan();
for (int i = 0; i < frameBuffer.Width; i++)
{
Rgb24 pixel = new();
pixel.R = yRow[i];
pixel.G = uRow[i];
pixel.B = vRow[i];
actual[i] = pixel;
}
Compare(referenceOutput, actual, 1);
}
[Fact]
public void YuvToRgbCompareToReferenceRandomPixels()
{
const int sampleCount = 1000;
// Assign
using Image<Rgb24> image = new(sampleCount, 1);
ImageFrame<Rgb24> frame = image.Frames.RootFrame;
ObuSequenceHeader sequenceHeader = new();
sequenceHeader.MaxFrameWidth = image.Width;
sequenceHeader.MaxFrameHeight = image.Height;
Av1FrameBuffer<byte> frameBuffer = new(Configuration.Default, sequenceHeader, Av1ColorFormat.Yuv444, false);
Random rnd = new(42);
CreateTestData(rnd, frameBuffer.BufferY.DangerousGetRowSpan(0));
CreateTestData(rnd, frameBuffer.BufferCb.DangerousGetRowSpan(0));
CreateTestData(rnd, frameBuffer.BufferCr.DangerousGetRowSpan(0));
// Act
Av1YuvConverter.ConvertToRgb(Configuration.Default, frameBuffer, frame);
Span<Rgb24> referenceOutput = Av1ReferenceYuvConverter.YuvToRgb(frameBuffer);
// Assert
frame.DangerousTryGetSinglePixelMemory(out Memory<Rgb24> memory);
Span<Rgb24> actual = memory.Span;
Compare(referenceOutput, actual, 1);
}
private static void Compare(Span<Rgb24> referenceOutput, Span<Rgb24> actual, int allowedDifference)
{
for (int i = 0; i < actual.Length; i++)
{
if (Math.Abs(referenceOutput[i].R - actual[i].R) > allowedDifference ||
Math.Abs(referenceOutput[i].G - actual[i].G) > allowedDifference ||
Math.Abs(referenceOutput[i].B - actual[i].B) > allowedDifference)
{
Assert.Fail($"Difference at index {i}, expected: {referenceOutput[i]} but was {actual[i]}");
}
}
}
private static void CreateTestData(Random rnd, Span<byte> span, int bitCount = 8)
{
int max = (1 << bitCount) - 1;
for (int i = 0; i < span.Length; i++)
{
byte current = (byte)rnd.Next(max);
span[i] = current;
}
}
private static void CreateTestData(Random rnd, Span<ushort> span, int bitCount)
{
int max = (1 << bitCount) - 1;
for (int i = 0; i < span.Length; i++)
{
ushort current = (ushort)rnd.Next(max);
span[i] = current;
}
}
[Theory]
[InlineData(255, 255, 255)]
[InlineData(0, 0, 0)]
@ -24,7 +177,7 @@ public class Av1YuvConverterTests
[InlineData(42, 0, 42)]
[InlineData(0, 42, 42)]
[InlineData(0, 0, 42)]
[InlineData(50, 100, 150)]
[InlineData(150, 100, 50)]
public void RoundTripSinglePixel(byte r, byte g, byte b)
{
// Assign

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