Add option to apply trellis quantization to the DC coefficients ( see
#57 ). May need further refinement to make sure block order during
trellis optimization matches order during coding.
From jpeglib-turbo r1221:
Integrate a slightly modified version of Mozilla's patch for
precomputing the bit-counting LUT. This is useful if the table needs
to be shared among multiple processes, although the primary reason for
doing that is reduced footprint on mobile devices, which are probably
already covered by the clz intrinsic code.
Optimizes quantization matrix by minimizing reconstruction error based
on quantized coefficients.
Feature is controlled by cinfo->trellis_q_opt; disabled by default.
Trellis quantization is modified:
- to work on the configurable spectral range Ss to Se
- to optionally optimize runs of EOBs
- to optionally split optimization between 2 spectral ranges
In trellis quantization passes Huffman table code optimization is
modified such as to generable a valid code length for each possible
symbol by resetting frequency counters to 1 instead of 0
Different lambda values may be used for each frequency in DCT domain.
The weighting table is currently not configurable but can be
enabled/disabled with cinfo-> use_lambda_weight_tbl
A new pass type trellis_pass is added. It defines a pass where trellis
quantization is done in the quantize_trellis() function.
Trellis quantization can be enabled by setting use_moz_defaults to 2 or
by using the -trellis option in cjpeg
Note that trellis does currently not work with scan optimization. Scan
optimization is disabled when trellis is enabled.
