Java Doc for StdEntropyCoder.java in  » 6.0-JDK-Modules » Java-Advanced-Imaging » jj2000 » j2k » entropy » encoder » Java Source Code / Java DocumentationJava Source Code and Java Documentation

The number of threads used by this entropy coder is specified by the "jj2000.j2k.entropy.encoder.StdEntropyCoder.nthreads" Java system property. If set to "0" the single threaded implementation is used. If set to 'n' ('n' larger than 0) then 'n' extra threads are started by this class which are used to encode the code-blocks in parallel (i.e. ideally 'n' code-blocks will be encoded in parallel at a time). On multiprocessor machines under a "native threads" Java Virtual Machine implementation each one of these threads can run on a separate processor speeding up the encoding time. By default the single-threaded implementation is used. The multi-threaded implementation currently assumes that the vast majority of consecutive calls to 'getNextCodeBlock()' will be done on the same component. If this is not the case, the speed-up that can be expected on multiprocessor machines might be significantly decreased.

The code-blocks are rectangular, with dimensions which must be powers of 2. Each dimension has to be no smaller than 4 and no larger than 256. The product of the two dimensions (i.e. area of the code-block) may not exceed 4096.

Context 0 of the MQ-coder is used as the uniform one (uniform, non-adaptive probability distribution). Context 1 is used for RLC coding. Contexts 2-10 are used for zero-coding (ZC), contexts 11-15 are used for sign-coding (SC) and contexts 16-18 are used for magnitude-refinement (MR).

This implementation buffers the symbols and calls the MQ coder only once per stripe and per coding pass, to reduce the method call overhead.

This implementation also provides some timing features. They can be enabled by setting the 'DO_TIMING' constant of this class to true and recompiling. The timing uses the 'System.currentTimeMillis()' Java API call, which returns wall clock time, not the actual CPU time used. The timing results will be printed on the message output. Since the times reported are wall clock times and not CPU usage times they can not be added to find the total used time (i.e. some time might be counted in several places). When timing is disabled ('DO_TIMING' is false) there is no penalty if the compiler performs some basic optimizations. Even if not the penalty should be negligeable.

The source module must implement the CBlkQuantDataSrcEnc interface and code-block's data is received in a CBlkWTData instance. This modules sends code-block's information in a CBlkRateDistStats instance.
See Also:   CBlkQuantDataSrcEnc
See Also:   CBlkWTData
See Also:   CBlkRateDistStats

If the 'OPT_PRED_TERM' option is given then the MQ termination must be 'TERM_PRED_ER' or an exception is thrown.

When changing the current tile (through 'setTile()' or 'nextTile()') this method will always return the first code-block, as if this method was never called before for the new current tile.

The data returned by this method is always a copy of the internal data of this object, if any, and it can be modified "in place" without any problems after being returned.
Parameters:
  c - The component for which to return the next code-block.
Parameters:
  ccb - If non-null this object might be used in returning the codedcode-block in this or any subsequent call to this method. If null a newone is created and returned. If the 'data' array of 'cbb' is not nullit may be reused to return the compressed data. The next coded code-block in the current tile for component'n', or null if all code-blocks for the current tile have beenreturned.
See Also:   CBlkRateDistStats

This default implementation just advances to the next tile in the source.

This default implementation just changes the tile in the source.
Parameters:
  x - The horizontal index of the tile.
Parameters:
  y - The vertical index of the new tile.