/// <summary>
/// Encodes the image with subsampling. The Cb and Cr components are each subsampled
/// at a factor of 2 both horizontally and vertically.
/// </summary>
/// <typeparam name="TPixel">The pixel format.</typeparam>
/// <param name="pixels">The pixel accessor providing access to the image pixels.</param>
private void Encode420 <TPixel>(Image <TPixel> pixels)
where TPixel : struct, IPixel <TPixel>
{
// TODO: Need a JpegScanEncoder<TPixel> class or struct that encapsulates the scan-encoding implementation. (Similar to JpegScanDecoder.)
Block8x8F b = default(Block8x8F);
BlockQuad cb = default(BlockQuad);
BlockQuad cr = default(BlockQuad);
Block8x8F *cbPtr = (Block8x8F *)cb.Data;
Block8x8F *crPtr = (Block8x8F *)cr.Data;
Block8x8F temp1 = default(Block8x8F);
Block8x8F temp2 = default(Block8x8F);
Block8x8F onStackLuminanceQuantTable = this.luminanceQuantTable;
Block8x8F onStackChrominanceQuantTable = this.chrominanceQuantTable;
ZigZag unzig = ZigZag.CreateUnzigTable();
var pixelConverter = YCbCrForwardConverter <TPixel> .Create();
// ReSharper disable once InconsistentNaming
int prevDCY = 0, prevDCCb = 0, prevDCCr = 0;
for (int y = 0; y < pixels.Height; y += 16)
{
for (int x = 0; x < pixels.Width; x += 16)
{
for (int i = 0; i < 4; i++)
{
int xOff = (i & 1) * 8;
int yOff = (i & 2) * 4;
pixelConverter.Convert(pixels.Frames.RootFrame, x + xOff, y + yOff);
cbPtr[i] = pixelConverter.Cb;
crPtr[i] = pixelConverter.Cr;
prevDCY = this.WriteBlock(
QuantIndex.Luminance,
prevDCY,
&pixelConverter.Y,
&temp1,
&temp2,
&onStackLuminanceQuantTable,
unzig.Data);
}
Block8x8F.Scale16X16To8X8(&b, cbPtr);
prevDCCb = this.WriteBlock(
QuantIndex.Chrominance,
prevDCCb,
&b,
&temp1,
&temp2,
&onStackChrominanceQuantTable,
unzig.Data);
Block8x8F.Scale16X16To8X8(&b, crPtr);
prevDCCr = this.WriteBlock(
QuantIndex.Chrominance,
prevDCCr,
&b,
&temp1,
&temp2,
&onStackChrominanceQuantTable,
unzig.Data);
}
}
}
public static unsafe float GetScalarAt(Block8x8F *blockPtr, int idx)
{
float *fp = (float *)blockPtr;
return(fp[idx]);
}
public static unsafe void LoadFrom(Block8x8F *blockPtr, MutableSpan <float> source)
{
Marshal.Copy(source.Data, source.Offset, (IntPtr)blockPtr, ScalarCount);
}
public static unsafe void CopyTo(Block8x8F *blockPtr, MutableSpan <float> dest)
{
Marshal.Copy((IntPtr)blockPtr, dest.Data, dest.Offset, ScalarCount);
}
public static unsafe void SetScalarAt(Block8x8F *blockPtr, int idx, float value)
{
float *fp = (float *)blockPtr;
fp[idx] = value;
}
