public static bool TryParse(ReadOnlySequence <byte> buffer, bool metadataOnly, out JpegScanHeader scanHeader, out int bytesConsumed)
{
if (buffer.IsSingleSegment)
{
return(TryParse(buffer.First.Span, metadataOnly, out scanHeader, out bytesConsumed));
}
bytesConsumed = 0;
if (buffer.IsEmpty)
{
scanHeader = default;
return(false);
}
byte numberOfComponents = buffer.First.Span[0];
buffer = buffer.Slice(1);
bytesConsumed++;
if (buffer.Length < (2 * numberOfComponents + 3))
{
scanHeader = default;
return(false);
}
JpegScanComponentSpecificationParameters[]? components;
if (metadataOnly)
{
components = null;
buffer = buffer.Slice(2 * numberOfComponents);
bytesConsumed += 2 * numberOfComponents;
}
else
{
components = new JpegScanComponentSpecificationParameters[numberOfComponents];
for (int i = 0; i < components.Length; i++)
{
#pragma warning disable CA1806
JpegScanComponentSpecificationParameters.TryParse(buffer, out components[i]);
#pragma warning restore CA1806
buffer = buffer.Slice(2);
bytesConsumed += 2;
}
}
Span <byte> local = stackalloc byte[4];
buffer.Slice(0, 3).CopyTo(local);
byte successiveApproximationBitPosition = local[2];
byte endOfSpectralSelection = local[1];
byte startOfSpectralSelection = local[0];
bytesConsumed += 3;
scanHeader = new JpegScanHeader(numberOfComponents, components, startOfSpectralSelection, endOfSpectralSelection, (byte)(successiveApproximationBitPosition >> 4), (byte)(successiveApproximationBitPosition & 0xf));
return(true);
}
public static bool TryParse(ReadOnlySpan <byte> buffer, out JpegScanComponentSpecificationParameters component)
{
if (buffer.Length < 2)
{
component = default;
return(false);
}
byte entropyCodingTableSelector = buffer[1];
byte scanComponentSelector = buffer[0];
component = new JpegScanComponentSpecificationParameters(scanComponentSelector, (byte)(entropyCodingTableSelector >> 4), (byte)(entropyCodingTableSelector & 0xf));
return(true);
}
public static bool TryParse(ReadOnlySequence <byte> buffer, out JpegScanComponentSpecificationParameters component)
{
if (buffer.IsSingleSegment)
{
return(TryParse(buffer.First.Span, out component));
}
if (buffer.Length < 2)
{
component = default;
return(false);
}
Span <byte> local = stackalloc byte[2];
buffer.Slice(0, 2).CopyTo(local);
byte entropyCodingTableSelector = local[1];
byte scanComponentSelector = local[0];
component = new JpegScanComponentSpecificationParameters(scanComponentSelector, (byte)(entropyCodingTableSelector >> 4), (byte)(entropyCodingTableSelector & 0xf));
return(true);
}
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);
}