Add progressive JPEG encoder

src/ImageSharp/Formats/Jpeg/Components/Decoder/HuffmanScanDecoder.cs

@@ -119,6 +119,8 @@ public void ParseEntropyCodedData(int scanComponentCount)
 
  this.frame.AllocateComponents();
 
+ this.todo = this.restartInterval;
+
  if (!this.frame.Progressive)
  {
  this.ParseBaselineData();

src/ImageSharp/Formats/Jpeg/Components/Encoder/HuffmanScanEncoder.cs

@@ -87,6 +87,8 @@ internal class HuffmanScanEncoder
  /// </remarks>
  private readonly byte[] streamWriteBuffer;
 
+ private readonly int restartInterval;
+
  /// <summary>
  /// Number of jagged bits stored in <see cref="accumulatedBits"/>
  /// </summary>
@@ -103,13 +105,16 @@ internal class HuffmanScanEncoder
  /// Initializes a new instance of the <see cref="HuffmanScanEncoder"/> class.
  /// </summary>
  /// <param name="blocksPerCodingUnit">Amount of encoded 8x8 blocks per single jpeg macroblock.</param>
+ /// <param name="restartInterval">Numbers of MCUs between restart markers.</param>
  /// <param name="outputStream">Output stream for saving encoded data.</param>
- public HuffmanScanEncoder(int blocksPerCodingUnit, Stream outputStream)
+ public HuffmanScanEncoder(int blocksPerCodingUnit, int restartInterval, Stream outputStream)
  {
  int emitBufferByteLength = MaxBytesPerBlock * blocksPerCodingUnit;
  this.emitBuffer = new uint[emitBufferByteLength / sizeof(uint)];
  this.emitWriteIndex = this.emitBuffer.Length;
 
+ this.restartInterval = restartInterval;
+
  this.streamWriteBuffer = new byte[emitBufferByteLength * OutputBufferLengthMultiplier];
 
  this.target = outputStream;
@@ -211,6 +216,9 @@ public void EncodeScanBaseline(Component component, CancellationToken cancellati
  ref HuffmanLut dcHuffmanTable = ref this.dcHuffmanTables[component.DcTableId];
  ref HuffmanLut acHuffmanTable = ref this.acHuffmanTables[component.AcTableId];
 
+ int restarts = 0;
+ int restartsToGo = this.restartInterval;
+
  for (int i = 0; i < h; i++)
  {
  cancellationToken.ThrowIfCancellationRequested();
@@ -221,6 +229,13 @@ public void EncodeScanBaseline(Component component, CancellationToken cancellati
 
  for (nuint k = 0; k < (uint)w; k++)
  {
+ if (this.restartInterval > 0 && restartsToGo == 0)
+ {
+ this.FlushRemainingBytes();
+ this.WriteRestart(restarts % 8);
+ component.DcPredictor = 0;
+ }
+
  this.WriteBlock(
  component,
  ref Unsafe.Add(ref blockRef, k),
@@ -231,6 +246,133 @@ ref Unsafe.Add(ref blockRef, k),
  {
  this.FlushToStream();
  }
+
+ if (this.restartInterval > 0)
+ {
+ if (restartsToGo == 0)
+ {
+ restartsToGo = this.restartInterval;
+ restarts++;
+ }
+
+ restartsToGo--;
+ }
+ }
+ }
+
+ this.FlushRemainingBytes();
+ }
+
+ /// <summary>
+ /// Encodes the DC coefficients for a given component's blocks in a scan.
+ /// </summary>
+ /// <param name="component">The component whose DC coefficients need to be encoded.</param>
+ /// <param name="cancellationToken">The token to request cancellation.</param>
+ public void EncodeDcScan(Component component, CancellationToken cancellationToken)
+ {
+ int h = component.HeightInBlocks;
+ int w = component.WidthInBlocks;
+
+ ref HuffmanLut dcHuffmanTable = ref this.dcHuffmanTables[component.DcTableId];
+
+ int restarts = 0;
+ int restartsToGo = this.restartInterval;
+
+ for (int i = 0; i < h; i++)
+ {
+ cancellationToken.ThrowIfCancellationRequested();
+
+ Span<Block8x8> blockSpan = component.SpectralBlocks.DangerousGetRowSpan(y: i);
+ ref Block8x8 blockRef = ref MemoryMarshal.GetReference(blockSpan);
+
+ for (nuint k = 0; k < (uint)w; k++)
+ {
+ if (this.restartInterval > 0 && restartsToGo == 0)
+ {
+ this.FlushRemainingBytes();
+ this.WriteRestart(restarts % 8);
+ component.DcPredictor = 0;
+ }
+
+ this.WriteDc(
+ component,
+ ref Unsafe.Add(ref blockRef, k),
+ ref dcHuffmanTable);
+
+ if (this.IsStreamFlushNeeded)
+ {
+ this.FlushToStream();
+ }
+
+ if (this.restartInterval > 0)
+ {
+ if (restartsToGo == 0)
+ {
+ restartsToGo = this.restartInterval;
+ restarts++;
+ }
+
+ restartsToGo--;
+ }
+ }
+ }
+
+ this.FlushRemainingBytes();
+ }
+
+ /// <summary>
+ /// Encodes the AC coefficients for a specified range of blocks in a component's scan.
+ /// </summary>
+ /// <param name="component">The component whose AC coefficients need to be encoded.</param>
+ /// <param name="start">The starting index of the AC coefficient range to encode.</param>
+ /// <param name="end">The ending index of the AC coefficient range to encode.</param>
+ /// <param name="cancellationToken">The token to request cancellation.</param>
+ public void EncodeAcScan(Component component, nint start, nint end, CancellationToken cancellationToken)
+ {
+ int h = component.HeightInBlocks;
+ int w = component.WidthInBlocks;
+
+ int restarts = 0;
+ int restartsToGo = this.restartInterval;
+
+ ref HuffmanLut acHuffmanTable = ref this.acHuffmanTables[component.AcTableId];
+
+ for (int i = 0; i < h; i++)
+ {
+ cancellationToken.ThrowIfCancellationRequested();
+
+ Span<Block8x8> blockSpan = component.SpectralBlocks.DangerousGetRowSpan(y: i);
+ ref Block8x8 blockRef = ref MemoryMarshal.GetReference(blockSpan);
+
+ for (nuint k = 0; k < (uint)w; k++)
+ {
+ if (this.restartInterval > 0 && restartsToGo == 0)
+ {
+ this.FlushRemainingBytes();
+ this.WriteRestart(restarts % 8);
+ }
+
+ this.WriteAcBlock(
+ ref Unsafe.Add(ref blockRef, k),
+ start,
+ end,
+ ref acHuffmanTable);
+
+ if (this.IsStreamFlushNeeded)
+ {
+ this.FlushToStream();
+ }
+
+ if (this.restartInterval > 0)
+ {
+ if (restartsToGo == 0)
+ {
+ restartsToGo = this.restartInterval;
+ restarts++;
+ }
+
+ restartsToGo--;
+ }
  }
  }
 
@@ -250,6 +392,9 @@ private void EncodeScanBaselineInterleaved<TPixel>(JpegFrame frame, SpectralConv
  int mcusPerColumn = frame.McusPerColumn;
  int mcusPerLine = frame.McusPerLine;
 
+ int restarts = 0;
+ int restartsToGo = this.restartInterval;
+
  for (int j = 0; j < mcusPerColumn; j++)
  {
  cancellationToken.ThrowIfCancellationRequested();
@@ -260,6 +405,16 @@ private void EncodeScanBaselineInterleaved<TPixel>(JpegFrame frame, SpectralConv
  // Encode spectral to binary
  for (int i = 0; i < mcusPerLine; i++)
  {
+ if (this.restartInterval > 0 && restartsToGo == 0)
+ {
+ this.FlushRemainingBytes();
+ this.WriteRestart(restarts % 8);
+ foreach (var component in frame.Components)
+ {
+ component.DcPredictor = 0;
+ }
+ }
+
  // Scan an interleaved mcu... process components in order
  int mcuCol = mcu % mcusPerLine;
  for (int k = 0; k < frame.Components.Length; k++)
@@ -300,6 +455,17 @@ ref Unsafe.Add(ref blockRef, blockCol),
  {
  this.FlushToStream();
  }
+
+ if (this.restartInterval > 0)
+ {
+ if (restartsToGo == 0)
+ {
+ restartsToGo = this.restartInterval;
+ restarts++;
+ }
+
+ restartsToGo--;
+ }
  }
  }
 
@@ -371,25 +537,29 @@ ref Unsafe.Add(ref c2BlockRef, i),
  this.FlushRemainingBytes();
  }
 
- private void WriteBlock(
+ private void WriteDc(
  Component component,
  ref Block8x8 block,
- ref HuffmanLut dcTable,
- ref HuffmanLut acTable)
+ ref HuffmanLut dcTable)
  {
  // Emit the DC delta.
  int dc = block[0];
  this.EmitHuffRLE(dcTable.Values, 0, dc - component.DcPredictor);
  component.DcPredictor = dc;
+ }
 
+ private void WriteAcBlock(
+ ref Block8x8 block,
+ nint start,
+ nint end,
+ ref HuffmanLut acTable)
+ {
  // Emit the AC components.
  int[] acHuffTable = acTable.Values;
 
- nint lastValuableIndex = block.GetLastNonZeroIndex();
-
  int runLength = 0;
  ref short blockRef = ref Unsafe.As<Block8x8, short>(ref block);
- for (nint zig = 1; zig <= lastValuableIndex; zig++)
+ for (nint zig = start; zig < end; zig++)
  {
  const int zeroRun1 = 1 << 4;
  const int zeroRun16 = 16 << 4;
@@ -413,14 +583,25 @@ private void WriteBlock(
  }
 
  // if mcu block contains trailing zeros - we must write end of block (EOB) value indicating that current block is over
- // this can be done for any number of trailing zeros, even when all 63 ac values are zero
- // (Block8x8F.Size - 1) == 63 - last index of the mcu elements
- if (lastValuableIndex != Block8x8F.Size - 1)
+ if (runLength > 0)
  {
  this.EmitHuff(acHuffTable, 0x00);
  }
  }
 
+ private void WriteBlock(
+ Component component,
+ ref Block8x8 block,
+ ref HuffmanLut dcTable,
+ ref HuffmanLut acTable)
+ {
+ this.WriteDc(component, ref block, ref dcTable);
+ this.WriteAcBlock(ref block, 1, 64, ref acTable);
+ }
+
+ private void WriteRestart(int restart) =>
+ this.target.Write([0xff, (byte)(JpegConstants.Markers.RST0 + restart)], 0, 2);
+
  /// <summary>
  /// Emits the most significant count of bits to the buffer.
  /// </summary>

src/ImageSharp/Formats/Jpeg/JpegEncoder.cs

@@ -13,6 +13,16 @@ public sealed class JpegEncoder : ImageEncoder
  /// </summary>
  private int? quality;
 
+ /// <summary>
+ /// Backing field for <see cref="ProgressiveScans"/>
+ /// </summary>
+ private int progressiveScans = 4;
+
+ /// <summary>
+ /// Backing field for <see cref="RestartInterval"/>
+ /// </summary>
+ private int restartInterval;
+
  /// <summary>
  /// Gets the quality, that will be used to encode the image. Quality
  /// index must be between 1 and 100 (compression from max to min).
@@ -33,6 +43,56 @@ public int? Quality
  }
  }
 
+ /// <summary>
+ /// Gets a value indicating whether progressive encoding is used.
+ /// </summary>
+ public bool Progressive { get; init; }
+
+ /// <summary>
+ /// Gets number of scans per component for progressive encoding.
+ /// Defaults to <value>4</value>.
+ /// </summary>
+ /// <remarks>
+ /// Number of scans must be between 2 and 64.
+ /// There is at least one scan for the DC coefficients and one for the remaining 63 AC coefficients.
+ /// </remarks>
+ /// <exception cref="ArgumentException">Progressive scans must be in [2..64] range.</exception>
+ public int ProgressiveScans
+ {
+ get => this.progressiveScans;
+ init
+ {
+ if (value is < 2 or > 64)
+ {
+ throw new ArgumentException("Progressive scans must be in [2..64] range.");
+ }
+
+ this.progressiveScans = value;
+ }
+ }
+
+ /// <summary>
+ /// Gets numbers of MCUs between restart markers.
+ /// Defaults to <value>0</value>.
+ /// </summary>
+ /// <remarks>
+ /// Currently supported in progressive encoding only.
+ /// </remarks>
+ /// <exception cref="ArgumentException">Restart interval must be in [0..65535] range.</exception>
+ public int RestartInterval
+ {
+ get => this.restartInterval;
+ init
+ {
+ if (value is < 0 or > 65535)
+ {
+ throw new ArgumentException("Restart interval must be in [0..65535] range.");
+ }
+
+ this.restartInterval = value;
+ }
+ }
+
  /// <summary>
  /// Gets the component encoding mode.
  /// </summary>