){kind=link}
/// <summary>
/// Refines non-zero entries of b in zig-zag order.
/// If <paramref name="nz" /> >= 0, the first <paramref name="nz" /> zero entries are skipped over.
/// </summary>
/// <param name="decoder">The decoder</param>
/// <param name="zig">The zig-zag start index</param>
/// <param name="nz">The non-zero entry</param>
/// <param name="delta">The low transform offset</param>
/// <returns>The <see cref="int" /></returns>
private int RefineNonZeroes(JpegDecoderCore decoder, int zig, int nz, int delta)
{
var b = this.pointers.Block;
for (; zig <= this.zigEnd; zig++)
{
int u = this.pointers.Unzig[zig];
float bu = Block8x8F.GetScalarAt(b, u);
// TODO: Are the equality comparsions OK with floating point values? Isn't an epsilon value necessary?
if (bu == 0)
{
if (nz == 0)
{
break;
}
nz--;
continue;
}
bool bit = decoder.DecodeBit();
if (!bit)
{
continue;
}
if (bu >= 0)
{
// b[u] += delta;
Block8x8F.SetScalarAt(b, u, bu + delta);
}
else
{
// b[u] -= delta;
Block8x8F.SetScalarAt(b, u, bu - delta);
}
}
return(zig);
}
/// <summary>
/// Decodes a successive approximation refinement block, as specified in section G.1.2.
/// </summary>
/// <param name="decoder">The decoder instance</param>
/// <param name="h">The Huffman tree</param>
/// <param name="delta">The low transform offset</param>
private void Refine(JpegDecoderCore decoder, ref HuffmanTree h, int delta)
{
Block8x8F *b = this.pointers.Block;
// Refining a DC component is trivial.
if (this.zigStart == 0)
{
if (this.zigEnd != 0)
{
throw new ImageFormatException("Invalid state for zig DC component");
}
bool bit = decoder.DecodeBit();
if (bit)
{
int stuff = (int)Block8x8F.GetScalarAt(b, 0);
// int stuff = (int)b[0];
stuff |= delta;
// b[0] = stuff;
Block8x8F.SetScalarAt(b, 0, stuff);
}
return;
}
// Refining AC components is more complicated; see sections G.1.2.2 and G.1.2.3.
int zig = this.zigStart;
if (this.eobRun == 0)
{
for (; zig <= this.zigEnd; zig++)
{
bool done = false;
int z = 0;
byte val = decoder.DecodeHuffman(ref h);
int val0 = val >> 4;
int val1 = val & 0x0f;
switch (val1)
{
case 0:
if (val0 != 0x0f)
{
this.eobRun = (ushort)(1 << val0);
if (val0 != 0)
{
this.eobRun |= (ushort)decoder.DecodeBits(val0);
}
done = true;
}
break;
case 1:
z = delta;
bool bit = decoder.DecodeBit();
if (!bit)
{
z = -z;
}
break;
default:
throw new ImageFormatException("Unexpected Huffman code");
}
if (done)
{
break;
}
zig = this.RefineNonZeroes(decoder, zig, val0, delta);
if (zig > this.zigEnd)
{
throw new ImageFormatException($"Too many coefficients {zig} > {this.zigEnd}");
}
if (z != 0)
{
// b[Unzig[zig]] = z;
Block8x8F.SetScalarAt(b, this.pointers.Unzig[zig], z);
}
}
}
if (this.eobRun > 0)
{
this.eobRun--;
this.RefineNonZeroes(decoder, zig, -1, delta);
}
}