private JpegScanHeader ProcessScanHeader(ref JpegReader reader, bool metadataOnly)
{
if (!reader.TryReadLength(out ushort length))
{
ThrowInvalidDataException(reader.ConsumedByteCount, "Unexpected end of input data when reading segment length.");
}
if (!reader.TryReadBytes(length, out ReadOnlySequence <byte> buffer))
{
ThrowInvalidDataException(reader.ConsumedByteCount, "Unexpected end of input data when reading segment content.");
}
if (!JpegScanHeader.TryParse(buffer, metadataOnly, out JpegScanHeader scanHeader, out int bytesConsumed))
{
ThrowInvalidDataException(reader.ConsumedByteCount - length + bytesConsumed, "Failed to parse scan header.");
}
return(scanHeader);
}
public void Optimize(bool strip = true)
{
if (_encodingTables.IsEmpty)
{
throw new InvalidOperationException();
}
IBufferWriter <byte> bufferWriter = _output ?? throw new InvalidOperationException();
JpegReader reader = new JpegReader(_inputBuffer);
var writer = new JpegWriter(bufferWriter, _minimumBufferSegmentSize);
bool eoiReached = false;
bool huffmanTableWritten = false;
bool quantizationTableWritten = false;
while (!eoiReached && !reader.IsEmpty)
{
if (!reader.TryReadMarker(out JpegMarker marker))
{
ThrowInvalidDataException(reader.ConsumedByteCount, "No marker found.");
return;
}
switch (marker)
{
case JpegMarker.StartOfImage:
writer.WriteMarker(marker);
break;
case JpegMarker.App0:
case JpegMarker.StartOfFrame0:
case JpegMarker.StartOfFrame1:
writer.WriteMarker(marker);
CopyMarkerData(ref reader, ref writer);
break;
case JpegMarker.StartOfFrame2:
ProcessFrameHeader(ref reader, false, true);
throw new InvalidDataException("Progressive JPEG is not supported currently.");
case JpegMarker.StartOfFrame3:
case JpegMarker.StartOfFrame5:
case JpegMarker.StartOfFrame6:
case JpegMarker.StartOfFrame7:
case JpegMarker.StartOfFrame9:
case JpegMarker.StartOfFrame10:
case JpegMarker.StartOfFrame11:
case JpegMarker.StartOfFrame13:
case JpegMarker.StartOfFrame14:
case JpegMarker.StartOfFrame15:
ThrowInvalidDataException(reader.ConsumedByteCount, $"This type of JPEG stream is not supported ({marker}).");
return;
case JpegMarker.DefineHuffmanTable:
if (!huffmanTableWritten)
{
WriteHuffmanTables(ref writer);
huffmanTableWritten = true;
}
break;
case JpegMarker.DefineQuantizationTable:
if (!quantizationTableWritten)
{
WriteQuantizationTables(ref writer);
quantizationTableWritten = true;
}
break;
case JpegMarker.StartOfScan:
writer.WriteMarker(marker);
ReadOnlySequence <byte> buffer = CopyMarkerData(ref reader, ref writer);
if (!JpegScanHeader.TryParse(buffer, false, out JpegScanHeader scanHeader, out _))
{
ThrowInvalidDataException(reader.ConsumedByteCount - (int)buffer.Length, "Failed to parse scan header.");
}
CopyScanBaseline(ref reader, ref writer, scanHeader);
break;
case JpegMarker.DefineRestart0:
case JpegMarker.DefineRestart1:
case JpegMarker.DefineRestart2:
case JpegMarker.DefineRestart3:
case JpegMarker.DefineRestart4:
case JpegMarker.DefineRestart5:
case JpegMarker.DefineRestart6:
case JpegMarker.DefineRestart7:
writer.WriteMarker(marker);
break;
case JpegMarker.EndOfImage:
writer.WriteMarker(JpegMarker.EndOfImage);
eoiReached = true;
break;
default:
if (strip)
{
SkipMarkerData(ref reader);
}
else
{
writer.WriteMarker(marker);
CopyMarkerData(ref reader, ref writer);
}
break;
}
}
writer.Flush();
}