Class CCITTRLE

java.lang.Object
org.apache.sis.internal.storage.inflater.PixelChannel
org.apache.sis.internal.storage.inflater.CompressionChannel
org.apache.sis.internal.storage.inflater.CCITTRLE
All Implemented Interfaces:
Closeable, AutoCloseable, Channel, ReadableByteChannel
final class CCITTRLE extends CompressionChannel
Inflater for values encoded with the CCITT Group 3, 1-Dimensional Modified Huffman run length encoding. This compression is described in section 10 of TIFF 6 specification. "Run length" (consecutive black or white pixels) are encoded with "words" having a variable number of bits. Example:
Run length encoding examples
Run length Encoding
0 0000110111
1 010
2 11
3 10
4 011
5 0011
Because the number of bits varies, leading zeros are significant. For example, "11" is not equivalent to "011", which is not equivalent to "0011" neither. Consequently, we cannot parse directly the bits as integer values.
Since:
1.1
Version:
1.3

  • Field Details

    • WHITE_RUNLENGTH_TREE

      private static final short[] WHITE_RUNLENGTH_TREE
      Modified Huffman tree for length of runs of white and black colors. This array is generated by the CCITTRLETest class, which will also verifies that those values are still corrects. This array is used for finding the "run length" associated to a sequence of bits like below:
      • If value at offset i is negative, then the result is ~RUNLENGTH_TREE[i].
      • Otherwise read a bit and choose a branch according the bit value:
        • If the bit is 0, continue tree traversal at i+1.
        • If the bit is 1, continue tree traversal at RUNLENGTH_TREE[i].

    • BLACK_RUNLENGTH_TREE

      private static final short[] BLACK_RUNLENGTH_TREE
      Modified Huffman tree for length of runs of white and black colors. This array is generated by the CCITTRLETest class, which will also verifies that those values are still corrects. This array is used for finding the "run length" associated to a sequence of bits like below:
      • If value at offset i is negative, then the result is ~RUNLENGTH_TREE[i].
      • Otherwise read a bit and choose a branch according the bit value:
        • If the bit is 0, continue tree traversal at i+1.
        • If the bit is 1, continue tree traversal at RUNLENGTH_TREE[i].

    • TERMINATING_LIMIT

      static final int TERMINATING_LIMIT
      Value after the last terminating run length. Run lengths equal or greater to this value must be added to the next value until a terminating value is found.
      See Also:

    • bitsPerRow

      private final int bitsPerRow
      Number of bits in an image row, ignoring sub-regions and subsampling.

    • remainingBitsInRow

      private int remainingBitsInRow
      Number of bits that we still have to read for current image row.

    • runIsWhite

      private boolean runIsWhite
      true if reading black color, or false if reading white color. The photometric interpretation ("White is zero" versus "Black is zero") does not need to be handled here; it is handled by the color model instead.

    • runLength

      private int runLength
      Number of black or white pixels to write in the destination buffer.

    • SIZE_SHIFT

      private static final int SIZE_SHIFT
      Bit shift to apply on 1 for obtaining 8 (2³ = 8).
      See Also:

  • Constructor Details

    • CCITTRLE

      CCITTRLE(ChannelDataInput input, StoreListeners listeners, int sourceWidth)
      Creates a new channel which will decompress data from the given input. The setInputRegion(long, long) method must be invoked after construction before a reading process can start.
      Parameters:
      input - the source of data to decompress.
      listeners - object where to report warnings.
      sourceWidth - number of pixels in a row of the source image.

  • Method Details

    • setInputRegion

      public void setInputRegion(long start, long byteCount) throws IOException
      Prepares this inflater for reading a new tile or a new band of a tile.
      Overrides:
      setInputRegion in class CompressionChannel
      Parameters:
      start - stream position where to start reading.
      byteCount - number of bytes to read from the input.
      Throws:
      IOException - if the stream cannot be seek to the given start position.

    • getRunLength

      final int getRunLength(short[] tree) throws IOException
      Returns the number of bits of white pixels or black pixels to append.
      Parameters:
      tree - WHITE_RUNLENGTH_TREE or BLACK_RUNLENGTH_TREE.
      Throws:
      IOException

    • read

      public int read(ByteBuffer target) throws IOException
      Decompresses some bytes from the input into the given destination buffer.
      Parameters:
      target - the buffer into which bytes are to be transferred.
      Returns:
      the number of bytes read, or -1 if end-of-stream.
      Throws:
      IOException - if some other I/O error occurs.