/// <summary>
/// Writes a block of pixel data using the given quantization table,
/// returning the post-quantized DC value of the DCT-transformed block.
/// The block is in natural (not zig-zag) order.
/// </summary>
/// <param name="index">The quantization table index.</param>
/// <param name="prevDC">The previous DC value.</param>
/// <param name="src">Source block</param>
/// <param name="tempDest1">Temporal block to be used as FDCT Destination</param>
/// <param name="tempDest2">Temporal block 2</param>
/// <param name="quant">Quantization table</param>
/// <param name="unzigPtr">The 8x8 Unzig block pointer</param>
/// <returns>
/// The <see cref="int"/>
/// </returns>
private int WriteBlock(
QuantIndex index,
int prevDC,
Block8x8F *src,
Block8x8F *tempDest1,
Block8x8F *tempDest2,
Block8x8F *quant,
int *unzigPtr)
{
DCT.TransformFDCT(ref *src, ref *tempDest1, ref *tempDest2);
Block8x8F.UnzigDivRound(tempDest1, tempDest2, quant, unzigPtr);
float *unziggedDestPtr = (float *)tempDest2;
int dc = (int)unziggedDestPtr[0];
// Emit the DC delta.
this.EmitHuffRLE((HuffIndex)((2 * (int)index) + 0), 0, dc - prevDC);
// Emit the AC components.
HuffIndex h = (HuffIndex)((2 * (int)index) + 1);
int runLength = 0;
for (int zig = 1; zig < Block8x8F.ScalarCount; zig++)
{
int ac = (int)unziggedDestPtr[zig];
if (ac == 0)
{
runLength++;
}
else
{
while (runLength > 15)
{
this.EmitHuff(h, 0xf0);
runLength -= 16;
}
this.EmitHuffRLE(h, runLength, ac);
runLength = 0;
}
}
if (runLength > 0)
{
this.EmitHuff(h, 0x00);
}
return(dc);
}
/// <summary>
/// Initializes quantization table.
/// </summary>
/// <param name="i">The quantization index.</param>
/// <param name="scale">The scaling factor.</param>
/// <param name="quant">The quantization table.</param>
private static void InitQuantizationTable(int i, int scale, ref Block8x8F quant)
{
for (int j = 0; j < Block8x8F.ScalarCount; j++)
{
int x = UnscaledQuant[i, j];
x = ((x * scale) + 50) / 100;
if (x < 1)
{
x = 1;
}
if (x > 255)
{
x = 255;
}
quant[j] = x;
}
}
internal void Clear()
{
// The cheapest way to do this in C#:
this = new Block8x8F();
}
/// <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="TColor">The pixel format.</typeparam>
/// <param name="pixels">The pixel accessor providing access to the image pixels.</param>
private void Encode420 <TColor>(PixelAccessor <TColor> pixels)
where TColor : struct, IPackedPixel, IEquatable <TColor>
{
// TODO: Need a JpegScanEncoder<TColor> 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;
UnzigData unzig = UnzigData.Create();
// ReSharper disable once InconsistentNaming
int prevDCY = 0, prevDCCb = 0, prevDCCr = 0;
using (PixelArea <TColor> rgbBytes = new PixelArea <TColor>(8, 8, ComponentOrder.Xyz))
{
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;
ToYCbCr(pixels, x + xOff, y + yOff, &b, cbPtr + i, crPtr + i, rgbBytes);
prevDCY = this.WriteBlock(
QuantIndex.Luminance,
prevDCY,
&b,
&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);
}
}
}
}
