/// <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="block">The block to write.</param>
/// <param name="index">The quantization table index.</param>
/// <param name="prevDC">The previous DC value.</param>
/// <returns></returns>
private int WriteBlock(Block block, QuantIndex index, int prevDC)
{
FDCT.Transform(block);
// Emit the DC delta.
int dc = Round(block[0], 8 * this.quant[(int)index][0]);
this.EmitHuffRLE((HuffIndex)(2 * (int)index + 0), 0, dc - prevDC);
// Emit the AC components.
var h = (HuffIndex)(2 * (int)index + 1);
int runLength = 0;
for (int zig = 1; zig < Block.BlockSize; zig++)
{
int ac = Round(block[Unzig[zig]], 8 * this.quant[(int)index][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>
/// Writes the descrete quantization tables.
/// </summary>
/// <param name="writer">The writer to write to the stream.</param>
private void WriteDescreteQuantizationTables(EndianBinaryWriter writer)
{
byte[] dqt = new byte[134];
// Write the define quantization table marker. Markers are always prefixed with with 0xff.
dqt[0] = JpegConstants.Markers.XFF;
dqt[1] = JpegConstants.Markers.DQT;
dqt[2] = 0x00;
dqt[3] = 0x84; // Length 132
this.fdct = new FDCT(this.quality);
int offset = 4;
for (int i = 0; i < 2; i++)
{
dqt[offset++] = (byte)i;
// TODO: Perf. Split and avoid allocation.
int[] tempArray = this.fdct.Quantum[i];
for (int j = 0; j < 64; j++)
{
dqt[offset++] = (byte)tempArray[ZigZag.ZigZagMap[j]];
}
}
writer.Write(dqt);
}
