Clean up the lossless JPEG feature
- Rename jpeg_simple_lossless() to jpeg_enable_lossless() and modify the
function so that it stores the lossless parameters directly in the Ss
and Al fields of jpeg_compress_struct rather than using a scan script.
- Move the cjpeg -lossless switch into "Switches for advanced users".
- Document the libjpeg API and run-time features that are unavailable in
lossless mode, and ensure that all parameters, functions, and switches
related to unavailable features are ignored or generate errors in
- Defer any action that depends on whether lossless mode is enabled
until jpeg_start_compress()/jpeg_start_decompress() is called.
- Document the purpose of the point transform value.
- "Codec" stands for coder/decoder, so it is a bit awkward to say
"lossless compression codec" and "lossless decompression codec".
Use "lossless compressor" and "lossless decompressor" instead.
- Restore backward API/ABI compatibility with libjpeg v6b:
* Move the new 'lossless' field from the exposed jpeg_compress_struct
and jpeg_decompress_struct structures into the opaque
jpeg_comp_master and jpeg_decomp_master structures, and allocate the
master structures in the body of jpeg_create_compress() and
* Remove the new 'process' field from jpeg_compress_struct and
jpeg_decompress_struct and replace it with the old
'progressive_mode' field and the new 'lossless' field.
* Remove the new 'data_unit' field from jpeg_compress_struct and
jpeg_decompress_struct and replace it with a locally-computed
data unit variable.
* Restore the names of macros and fields that refer to DCT blocks, and
document that they have a different meaning in lossless mode. (Most
of them aren't very meaningful in lossless mode anyhow.)
* Remove the new alloc_darray() method from jpeg_memory_mgr and
replace it with an internal macro that wraps the alloc_sarray()
* Move the JDIFF* data types from jpeglib.h and jmorecfg.h into
* Remove the new 'codec' field from jpeg_compress_struct and
jpeg_decompress_struct and instead reuse the existing internal
coefficient control, forward/inverse DCT, and entropy
encoding/decoding structures for lossless compression/decompression.
* Repurpose existing error codes rather than introducing new ones.
(The new JERR_BAD_RESTART and JWRN_MUST_DOWNSCALE codes remain,
although JWRN_MUST_DOWNSCALE will probably be removed in
libjpeg-turbo, since we have a different way of handling multiple
- Automatically enable lossless mode when a scan script with parameters
that are only valid for lossless mode is detected, and document the
use of scan scripts to generate lossless JPEG images.
- Move the sequential and shared Huffman routines back into jchuff.c and
jdhuff.c, and document that those routines are shared with jclhuff.c
and jdlhuff.c as well as with jcphuff.c and jdphuff.c.
- Move MAX_DIFF_BITS from jchuff.h into jclhuff.c, the only place where
it is used.
- Move the predictor and scaler code into jclossls.c and jdlossls.c.
- Streamline register usage in the [un]differencers (inspired by similar
optimizations in the color [de]converters.)
- Restructure the logic in a few places to reduce duplicated code.
- Ensure that all lossless-specific code is guarded by
C_LOSSLESS_SUPPORTED or D_LOSSLESS_SUPPORTED and that the library can
be built successfully if either or both of those macros is undefined.
- Remove all short forms of external names introduced by the lossless
JPEG patch. (These will not be needed by libjpeg-turbo, so there is
no use cleaning them up.)
- Various wordsmithing, formatting, and punctuation tweaks
- Eliminate various compiler warnings.
67 files changed