private static void Decode1DScanline(ref BitReader bitReader, bool whiteIsZero, Span <byte> scanline)
{
int width = scanline.Length;
// Process every code word in this scanline
byte fillValue = whiteIsZero ? (byte)0 : (byte)255;
CcittDecodingTable currentTable = CcittDecodingTable.WhiteInstance;
CcittDecodingTable otherTable = CcittDecodingTable.BlackInstance;
int unpacked = 0;
while (true)
{
int runLength = currentTable.DecodeRun(ref bitReader);
if ((uint)runLength > (uint)scanline.Length)
{
throw new InvalidOperationException();
}
scanline.Slice(0, runLength).Fill(fillValue);
scanline = scanline.Slice(runLength);
unpacked += runLength;
// Switch to the other color.
fillValue = (byte)~fillValue;
CcittHelper.SwapTable(ref currentTable, ref otherTable);
if (unpacked == width)
{
// This line is fully unpacked. Should exit and process next line.
break;
}
}
}
/// <inheritdoc />
public void Decompress(TiffDecompressionContext context, ReadOnlyMemory <byte> input, Memory <byte> output)
{
if (context is null)
{
throw new ArgumentNullException(nameof(context));
}
if (context.PhotometricInterpretation != TiffPhotometricInterpretation.WhiteIsZero && context.PhotometricInterpretation != TiffPhotometricInterpretation.BlackIsZero)
{
throw new NotSupportedException("T4 compression does not support this photometric interpretation.");
}
if (context.BitsPerSample.Count != 1 || context.BitsPerSample[0] != 1)
{
throw new NotSupportedException("Unsupported bits per sample.");
}
ReadOnlySpan <byte> inputSpan = input.Span;
Span <byte> scanlinesBufferSpan = output.Span;
bool whiteIsZero = context.PhotometricInterpretation == TiffPhotometricInterpretation.WhiteIsZero;
int width = context.ImageSize.Width;
int height = context.SkippedScanlines + context.RequestedScanlines;
var bitReader = new BitReader(inputSpan, higherOrderBitsFirst: _higherOrderBitsFirst);
// Skip the first EOL code
if (bitReader.Peek(12) == 0b000000000001) // EOL code is 000000000001 (12bits).
{
bitReader.Advance(12);
}
else if (bitReader.Peek(16) == 1) // Or EOL code is zero filled.
{
bitReader.Advance(16);
}
// Process every scanline
for (int i = 0; i < height; i++)
{
if (scanlinesBufferSpan.Length < width)
{
throw new InvalidDataException();
}
Span <byte> scanline = scanlinesBufferSpan.Slice(0, width);
scanlinesBufferSpan = scanlinesBufferSpan.Slice(width);
// Process every code word in this scanline
byte fillValue = whiteIsZero ? (byte)0 : (byte)255;
CcittDecodingTable currentTable = CcittDecodingTable.WhiteInstance;
CcittDecodingTable otherTable = CcittDecodingTable.BlackInstance;
int unpacked = 0;
CcittCodeValue tableEntry;
while (true)
{
uint value = bitReader.Peek(16);
if (!currentTable.TryLookup(value, out tableEntry))
{
throw new InvalidDataException();
}
if (tableEntry.IsEndOfLine)
{
// fill the rest of scanline
scanline.Fill(fillValue);
bitReader.Advance(tableEntry.BitsRequired);
break;
}
// Check to see whether we are encountering a "filled" EOL ?
if ((value & 0b1111111111110000) == 0)
{
// Align to 8 bits
int filledBits = 8 - (bitReader.ConsumedBits + 12) % 8;
if (bitReader.Peek(filledBits) != 0)
{
throw new InvalidDataException();
}
// Confirm it is indeed an EOL code.
value = bitReader.Read(filledBits + 12);
if (value == 0b000000000001)
{
// fill the rest of scanline
scanline.Fill(fillValue);
break;
}
throw new InvalidDataException();
}
// Process normal code.
int runLength = tableEntry.RunLength;
scanline.Slice(0, runLength).Fill(fillValue);
scanline = scanline.Slice(runLength);
unpacked += runLength;
bitReader.Advance(tableEntry.BitsRequired);
// Terminating code is met. Switch to the other color.
if (tableEntry.IsTerminatingCode)
{
fillValue = (byte)~fillValue;
CcittHelper.SwapTable(ref currentTable, ref otherTable);
// This line is fully unpacked. Should exit and process next line.
if (unpacked == width)
{
// If this is the last line of the image, we don't process any code after this.
if (i == height - 1)
{
break;
}
// Is the next code word EOL ?
value = bitReader.Peek(16);
if ((value >> 4) == 0b000000000001)
{
// Skip the EOL code
bitReader.Advance(12);
break;
}
// Maybe the EOL is zero filled? First align to 8 bits
int filledBits = 8 - (bitReader.ConsumedBits + 12) % 8;
if (bitReader.Peek(filledBits) != 0)
{
bitReader.AdvanceAlignByte();
break;
}
// Confirm it is indeed an EOL code.
value = bitReader.Peek(filledBits + 12);
if (value == 0b000000000001)
{
bitReader.Advance(filledBits + 12);
}
bitReader.AdvanceAlignByte();
break;
}
}
}
}
}
private static void Decode2DScanline(ref BitReader bitReader, bool whiteIsZero, ReferenceScanline referenceScanline, Span <byte> scanline)
{
int width = scanline.Length;
CcittDecodingTable currentTable = CcittDecodingTable.WhiteInstance;
CcittDecodingTable otherTable = CcittDecodingTable.BlackInstance;
CcittTwoDimensionalDecodingTable decodingTable = CcittTwoDimensionalDecodingTable.Instance;
CcittTwoDimensionalCodeValue tableEntry;
const int PeekCount = CcittTwoDimensionalDecodingTable.PeekCount;
// 2D Encoding variables.
int a0 = -1, a1, b1;
byte fillByte = whiteIsZero ? (byte)0 : (byte)255;
// Process every code word in this scanline
int unpacked = 0;
while (true)
{
// Read next code word and advance pass it.
int value = (int)bitReader.Peek(PeekCount); // PeekCount = 12
// Special case handling for EOL.
// Lucky we don't need to peek again for EOL, because PeekCount(12) is excatly the length of EOL code.
if (value == 0b000000000001)
{
scanline.Fill(fillByte);
break;
}
// Look up in the table and advance past this code.
if (!decodingTable.TryLookup(value, out tableEntry))
{
throw new InvalidDataException();
}
bitReader.Advance(tableEntry.BitsRequired);
// Update 2D Encoding variables.
b1 = referenceScanline.FindB1(a0, fillByte);
// Switch on the code word.
switch (tableEntry.Type)
{
case CcittTwoDimensionalCodeType.Pass:
int b2 = referenceScanline.FindB2(b1);
scanline.Slice(unpacked, b2 - unpacked).Fill(fillByte);
unpacked = b2;
a0 = b2;
break;
case CcittTwoDimensionalCodeType.Horizontal:
// Decode M(a0a1)
int runLength = currentTable.DecodeRun(ref bitReader);
if ((uint)runLength > (uint)(scanline.Length - unpacked))
{
throw new InvalidOperationException();
}
scanline.Slice(unpacked, runLength).Fill(fillByte);
unpacked += runLength;
fillByte = (byte)~fillByte;
CcittHelper.SwapTable(ref currentTable, ref otherTable);
// Decode M(a1a2)
runLength = currentTable.DecodeRun(ref bitReader);
if ((uint)runLength > (uint)(scanline.Length - unpacked))
{
throw new InvalidOperationException();
}
scanline.Slice(unpacked, runLength).Fill(fillByte);
unpacked += runLength;
fillByte = (byte)~fillByte;
CcittHelper.SwapTable(ref currentTable, ref otherTable);
// Prepare next a0
a0 = unpacked;
break;
case CcittTwoDimensionalCodeType.Vertical0:
a1 = b1;
scanline.Slice(unpacked, a1 - unpacked).Fill(fillByte);
unpacked = a1;
a0 = a1;
fillByte = (byte)~fillByte;
CcittHelper.SwapTable(ref currentTable, ref otherTable);
break;
case CcittTwoDimensionalCodeType.VerticalR1:
a1 = b1 + 1;
scanline.Slice(unpacked, a1 - unpacked).Fill(fillByte);
unpacked = a1;
a0 = a1;
fillByte = (byte)~fillByte;
CcittHelper.SwapTable(ref currentTable, ref otherTable);
break;
case CcittTwoDimensionalCodeType.VerticalR2:
a1 = b1 + 2;
scanline.Slice(unpacked, a1 - unpacked).Fill(fillByte);
unpacked = a1;
a0 = a1;
fillByte = (byte)~fillByte;
CcittHelper.SwapTable(ref currentTable, ref otherTable);
break;
case CcittTwoDimensionalCodeType.VerticalR3:
a1 = b1 + 3;
scanline.Slice(unpacked, a1 - unpacked).Fill(fillByte);
unpacked = a1;
a0 = a1;
fillByte = (byte)~fillByte;
CcittHelper.SwapTable(ref currentTable, ref otherTable);
break;
case CcittTwoDimensionalCodeType.VerticalL1:
a1 = b1 - 1;
scanline.Slice(unpacked, a1 - unpacked).Fill(fillByte);
unpacked = a1;
a0 = a1;
fillByte = (byte)~fillByte;
CcittHelper.SwapTable(ref currentTable, ref otherTable);
break;
case CcittTwoDimensionalCodeType.VerticalL2:
a1 = b1 - 2;
scanline.Slice(unpacked, a1 - unpacked).Fill(fillByte);
unpacked = a1;
a0 = a1;
fillByte = (byte)~fillByte;
CcittHelper.SwapTable(ref currentTable, ref otherTable);
break;
case CcittTwoDimensionalCodeType.VerticalL3:
a1 = b1 - 3;
scanline.Slice(unpacked, a1 - unpacked).Fill(fillByte);
unpacked = a1;
a0 = a1;
fillByte = (byte)~fillByte;
CcittHelper.SwapTable(ref currentTable, ref otherTable);
break;
default:
throw new NotSupportedException("1D and 2D Extensions not supportted.");
}
// This line is fully unpacked. Should exit and process next line.
if (unpacked == width)
{
break;
}
else if (unpacked > width)
{
throw new InvalidDataException();
}
}
}
/// <inheritdoc />
public void Decompress(TiffDecompressionContext context, ReadOnlyMemory <byte> input, Memory <byte> output)
{
if (context is null)
{
throw new ArgumentNullException(nameof(context));
}
if (context.PhotometricInterpretation != TiffPhotometricInterpretation.WhiteIsZero && context.PhotometricInterpretation != TiffPhotometricInterpretation.BlackIsZero)
{
throw new NotSupportedException("Modified Huffman compression does not support this photometric interpretation.");
}
if (context.BitsPerSample.Count != 1 || context.BitsPerSample[0] != 1)
{
throw new NotSupportedException("Unsupported bits per sample.");
}
ReadOnlySpan <byte> inputSpan = input.Span;
Span <byte> scanlinesBufferSpan = output.Span;
bool whiteIsZero = context.PhotometricInterpretation == TiffPhotometricInterpretation.WhiteIsZero;
int width = context.ImageSize.Width;
int height = context.SkippedScanlines + context.RequestedScanlines;
var bitReader = new BitReader(inputSpan, higherOrderBitsFirst: _higherOrderBitsFirst);
// Process every scanline
for (int i = 0; i < height; i++)
{
if (scanlinesBufferSpan.Length < width)
{
throw new InvalidDataException();
}
Span <byte> scanline = scanlinesBufferSpan.Slice(0, width);
scanlinesBufferSpan = scanlinesBufferSpan.Slice(width);
// Process every code word in this scanline
byte fillValue = whiteIsZero ? (byte)0 : (byte)255;
CcittDecodingTable currentTable = CcittDecodingTable.WhiteInstance;
CcittDecodingTable otherTable = CcittDecodingTable.BlackInstance;
int unpacked = 0;
while (true)
{
if (!currentTable.TryLookup(bitReader.Peek(16), out CcittCodeValue tableEntry))
{
throw new InvalidDataException();
}
if (tableEntry.IsEndOfLine)
{
// EOL code is not used in modified huffman algorithm
throw new InvalidDataException();
}
// Process normal code.
int runLength = tableEntry.RunLength;
scanline.Slice(0, runLength).Fill(fillValue);
scanline = scanline.Slice(runLength);
unpacked += runLength;
bitReader.Advance(tableEntry.BitsRequired);
// Terminating code is met. Switch to the other color.
if (tableEntry.IsTerminatingCode)
{
fillValue = (byte)~fillValue;
CcittHelper.SwapTable(ref currentTable, ref otherTable);
// This line is fully unpacked. Should exit and process next line.
if (unpacked == width)
{
break;
}
}
}
bitReader.AdvanceAlignByte();
}
}