Class PackBitsDecoder

java.lang.Object
com.twelvemonkeys.io.enc.PackBitsDecoder
All Implemented Interfaces:
Decoder

public final class PackBitsDecoder extends Object implements Decoder
Decoder implementation for Apple PackBits run-length encoding.

From Wikipedia, the free encyclopedia
PackBits is a fast, simple compression scheme for run-length encoding of data.

Apple introduced the PackBits format with the release of MacPaint on the Macintosh computer. This compression scheme is one of the types of compression that can be used in TIFF-files.

A PackBits data stream consists of packets of one byte of header followed by data. The header is a signed byte; the data can be signed, unsigned, or packed (such as MacPaint pixels).

PackBits
Header byteData
0 to 127 1 + n literal bytes of data
0 to -127 One byte of data, repeated 1 - n times in the decompressed output
-128 No operation

Note that interpreting 0 as positive or negative makes no difference in the output. Runs of two bytes adjacent to non-runs are typically written as literal data.

Version:
$Id: //depot/branches/personal/haraldk/twelvemonkeys/release-2/twelvemonkeys-core/src/main/java/com/twelvemonkeys/io/enc/PackBitsDecoder.java#1 $
Author:
Harald Kuhr
See Also:
  • Constructor Details

    • PackBitsDecoder

      public PackBitsDecoder()
      Creates a PackBitsDecoder.
    • PackBitsDecoder

      public PackBitsDecoder(boolean disableNoOp)
      Creates a PackBitsDecoder, with optional compatibility mode.

      As some implementations of PackBits-like encoders treat -128 as length of a compressed run, instead of a no-op, it's possible to disable no-ops for compatibility. Should be used with caution, even though, most known encoders never write no-ops in the compressed streams.

      Parameters:
      disableNoOp - true if -128 should be treated as a compressed run, and not a no-op
    • PackBitsDecoder

      public PackBitsDecoder(int sampleSize, boolean disableNoOp)
      Creates a PackBitsDecoder, with optional compatibility mode.

      As some implementations of PackBits-like encoders treat -128 as length of a compressed run, instead of a no-op, it's possible to disable no-ops for compatibility. Should be used with caution, even though, most known encoders never write no-ops in the compressed streams.

      Parameters:
      disableNoOp - true if -128 should be treated as a compressed run, and not a no-op
  • Method Details

    • decode

      public int decode(InputStream stream, ByteBuffer buffer) throws IOException
      Decodes bytes from the given input stream, to the given buffer.
      Specified by:
      decode in interface Decoder
      Parameters:
      stream - the stream to decode from
      buffer - a byte array, minimum 128 (or 129 if no-op is disabled) bytes long
      Returns:
      The number of bytes decoded
      Throws:
      IOException - if a problem occurs during decoding.