/// <summary>
/// Convert raw spectral DCT data to color data and copy it to the color buffer <see cref="ColorBuffer"/>.
/// </summary>
public void CopyBlocksToColorBuffer(int spectralStep)
{
Buffer2D <Block8x8> spectralBuffer = this.component.SpectralBlocks;
float maximumValue = this.frame.MaxColorChannelValue;
int destAreaStride = this.ColorBuffer.Width;
int yBlockStart = spectralStep * this.blockRowsPerStep;
Size subSamplingDivisors = this.component.SubSamplingDivisors;
Block8x8F dequantTable = this.rawJpeg.QuantizationTables[this.component.QuantizationTableIndex];
Block8x8F workspaceBlock = default;
for (int y = 0; y < this.blockRowsPerStep; y++)
{
int yBuffer = y * this.blockAreaSize.Height;
Span <float> colorBufferRow = this.ColorBuffer.DangerousGetRowSpan(yBuffer);
Span <Block8x8> blockRow = spectralBuffer.DangerousGetRowSpan(yBlockStart + y);
for (int xBlock = 0; xBlock < spectralBuffer.Width; xBlock++)
{
// Integer to float
workspaceBlock.LoadFrom(ref blockRow[xBlock]);
// Dequantize
workspaceBlock.MultiplyInPlace(ref dequantTable);
// Convert from spectral to color
FastFloatingPointDCT.TransformIDCT(ref workspaceBlock);
// To conform better to libjpeg we actually NEED TO loose precision here.
// This is because they store blocks as Int16 between all the operations.
// To be "more accurate", we need to emulate this by rounding!
workspaceBlock.NormalizeColorsAndRoundInPlace(maximumValue);
// Write to color buffer acording to sampling factors
int xColorBufferStart = xBlock * this.blockAreaSize.Width;
workspaceBlock.ScaledCopyTo(
ref colorBufferRow[xColorBufferStart],
destAreaStride,
subSamplingDivisors.Width,
subSamplingDivisors.Height);
}
}
}