private static int DecodeHuffmanCode(ref JpegBitReader reader, JpegHuffmanDecodingTable table)
{
int bits = reader.PeekBits(16, out int bitsRead);
JpegHuffmanDecodingTable.Entry entry = table.Lookup(bits);
bitsRead = Math.Min(entry.CodeSize, bitsRead);
_ = reader.TryAdvanceBits(bitsRead, out _);
return(entry.SymbolValue);
}
private static int Receive(ref JpegBitReader reader, int length)
{
Debug.Assert(length > 0);
if (!reader.TryReadBits(length, out int value, out bool isMarkerEncountered))
{
if (isMarkerEncountered)
{
ThrowInvalidDataException("Expect raw data from bit stream. Yet a marker is encountered.");
}
ThrowInvalidDataException("The bit stream ended prematurely.");
}
return(value);
}
private static void CopyBlockBaseline(ref JpegBitReader reader, ref JpegWriter writer, JpegTranscodeComponent component)
{
Debug.Assert(!(component.DcTable is null));
Debug.Assert(!(component.DcEncodingTable is null));
Debug.Assert(!(component.AcTable is null));
Debug.Assert(!(component.AcEncodingTable is null));
// DC
int symbol = DecodeHuffmanCode(ref reader, component.DcTable !);
component.DcEncodingTable !.GetCode(symbol, out ushort code, out int codeLength);
writer.WriteBits(code, codeLength);
if (symbol != 0)
{
int received = Receive(ref reader, symbol);
writer.WriteBits((uint)received, symbol);
}
// AC
for (int i = 1; i < 64;)
{
symbol = DecodeHuffmanCode(ref reader, component.AcTable !);
component.AcEncodingTable !.GetCode(symbol, out code, out codeLength);
writer.WriteBits(code, codeLength);
int r = symbol >> 4;
symbol &= 15;
if (symbol != 0)
{
i += r + 1;
int received = Receive(ref reader, symbol);
writer.WriteBits((uint)received, symbol);
}
else
{
if (r == 0)
{
break;
}
i += 16;
}
}
}
private static void ProcessBlockBaseline(ref JpegBitReader reader, JpegTranscodeComponent component)
{
Debug.Assert(!(component.DcTable is null));
Debug.Assert(!(component.DcTableBuilder is null));
Debug.Assert(!(component.AcTable is null));
Debug.Assert(!(component.AcTableBuilder is null));
// DC
int t = DecodeHuffmanCode(ref reader, component.DcTable !);
component.DcTableBuilder !.IncrementCodeCount(t);
if (t != 0)
{
Receive(ref reader, t);
}
// AC
for (int i = 1; i < 64;)
{
int s = DecodeHuffmanCode(ref reader, component.AcTable !);
component.AcTableBuilder !.IncrementCodeCount(s);
int r = s >> 4;
s &= 15;
if (s != 0)
{
i += r;
i++;
Receive(ref reader, s);
}
else
{
if (r == 0)
{
break;
}
i += 16;
}
}
}
private void CopyScanBaseline(ref JpegReader reader, ref JpegWriter writer, JpegScanHeader scanHeader)
{
JpegFrameHeader frameHeader = _frameHeader.GetValueOrDefault();
if (scanHeader.Components is null)
{
throw new InvalidOperationException();
}
// Compute maximum sampling factor
byte maxHorizontalSampling = 1;
byte maxVerticalSampling = 1;
foreach (JpegFrameComponentSpecificationParameters currentFrameComponent in frameHeader.Components !)
{
maxHorizontalSampling = Math.Max(maxHorizontalSampling, currentFrameComponent.HorizontalSamplingFactor);
maxVerticalSampling = Math.Max(maxVerticalSampling, currentFrameComponent.VerticalSamplingFactor);
}
// Resolve each component
JpegTranscodeComponent[] components = new JpegTranscodeComponent[scanHeader.NumberOfComponents];
for (int i = 0; i < scanHeader.NumberOfComponents; i++)
{
JpegScanComponentSpecificationParameters scanComponenet = scanHeader.Components[i];
int componentIndex = 0;
JpegFrameComponentSpecificationParameters?frameComponent = null;
for (int j = 0; j < frameHeader.NumberOfComponents; j++)
{
JpegFrameComponentSpecificationParameters currentFrameComponent = frameHeader.Components[j];
if (scanComponenet.ScanComponentSelector == currentFrameComponent.Identifier)
{
componentIndex = j;
frameComponent = currentFrameComponent;
}
}
if (frameComponent is null)
{
throw new InvalidDataException();
}
components[i] = new JpegTranscodeComponent
{
ComponentIndex = componentIndex,
HorizontalSamplingFactor = frameComponent.GetValueOrDefault().HorizontalSamplingFactor,
VerticalSamplingFactor = frameComponent.GetValueOrDefault().VerticalSamplingFactor,
DcTable = GetHuffmanTable(true, scanComponenet.DcEntropyCodingTableSelector),
AcTable = GetHuffmanTable(false, scanComponenet.AcEntropyCodingTableSelector),
DcEncodingTable = _encodingTables.GetTable(true, scanComponenet.DcEntropyCodingTableSelector),
AcEncodingTable = _encodingTables.GetTable(false, scanComponenet.AcEntropyCodingTableSelector)
};
}
// Prepare
int mcusPerLine = (frameHeader.SamplesPerLine + 8 * maxHorizontalSampling - 1) / (8 * maxHorizontalSampling);
int mcusPerColumn = (frameHeader.NumberOfLines + 8 * maxVerticalSampling - 1) / (8 * maxVerticalSampling);
JpegBitReader bitReader = new JpegBitReader(reader.RemainingBytes);
int mcusBeforeRestart = _restartInterval;
bool eoiReached = false;
writer.EnterBitMode();
for (int rowMcu = 0; rowMcu < mcusPerColumn && !eoiReached; rowMcu++)
{
for (int colMcu = 0; colMcu < mcusPerLine && !eoiReached; colMcu++)
{
foreach (JpegTranscodeComponent component in components)
{
int h = component.HorizontalSamplingFactor;
int v = component.VerticalSamplingFactor;
for (int y = 0; y < v; y++)
{
for (int x = 0; x < h; x++)
{
CopyBlockBaseline(ref bitReader, ref writer, component);
}
}
}
if (_restartInterval > 0 && (--mcusBeforeRestart) == 0)
{
bitReader.AdvanceAlignByte();
JpegMarker marker = bitReader.TryReadMarker();
if (marker == JpegMarker.EndOfImage)
{
eoiReached = true;
break;
}
if (!marker.IsRestartMarker())
{
throw new InvalidOperationException("Expect restart marker.");
}
mcusBeforeRestart = _restartInterval;
writer.ExitBitMode();
writer.WriteMarker(marker);
writer.EnterBitMode();
}
}
}
bitReader.AdvanceAlignByte();
writer.ExitBitMode();
int bytesConsumed = reader.RemainingByteCount - bitReader.RemainingBits / 8;
if (eoiReached)
{
bytesConsumed -= 2;
}
else if (bitReader.TryPeekMarker() != 0)
{
if (!bitReader.TryPeekMarker().IsRestartMarker())
{
bytesConsumed -= 2;
}
}
reader.TryAdvance(bytesConsumed);
}