PNG compression level setting API: this allows the various compression settings
controlling deflate, fitlering, and so on to be set via a single setting with
six values. This is currently documented in png.h ("Write compression
settings").
Internally the compression settings have been tuned both for the overall setting
and for any specific settings made by the original APIs.
APIs to control iCCP chunk compression separately have been added.
contrib/examples/pngcp.c has been modified to accomodate the new compression
setting and to include options for separate control of iCCP chunk compression.
The new ABI, png_setting, has been modified to accomodate a wider range of
settings and most of the old compression control ABIs have been replaced by
function-like macros with the same API which call png_setting. This is an API
check in 1.7.0 for png_setting (alone). png_setting now handles all of
png_set_option. This eliminates 19 ABIs at the cost of adding 1 (png_setting).
CRC and benign error checking has been updated internally to use bit-fields and
the CRC calculation skip when the CRC is not used has been improved slightly to
avoid the initialization of the CRC. A new png_setting based API allows more
detailed control of benign error/warning messages (this may change, the internal
error handling seems too complex.) The ERROR_NUMBERS support has been removed
with the intent of implementing proper i18n.
The memcpy-size-0 issue in png_push_fill_buffer has been fixed, with an
appropriate debug() assert if a fill for 0 bytes occurs.
Most PNG_FLAG_ values for png_struct::flags have been eliminated (as a result of
the benign error handling changes). Only one remains.
Signed-off-by: John Bowler <jbowler@acm.org>
Palette index checking: checking on read was erroneously skipped. pngcp can now
turn off the palette index checking or fix the errors (mainly to allow
comparison with libpng 1.6, which defaulted to ignoring it). The API now
documents how the 'enabled' parameter works. On read the check is on by default
(it was apparently off in libpng 1.6) however now if explicitly turned on the
warning message is stopped, this provides better interaction with
get_palette_max at the cost of a small API change (may need to be reviewed.)
Palette size errors: invalid entries in the palette are now set to #beaded to
make the errors more obvious and allow easy detection in memory.
Read transform pipeline caching: changes to fix the palette index check (which
are erroneously cached), the pipeline can now contain multiple caches. E.g.
caching of packing of palette indices can be combined with caching of palette
RGB transforms.
Read code now checks for callbacks to read 0 data (and faults them). Fixed the
reading of PNGs with multiple 0 length IDATs that failed as a result plus the
handling of zero length unknown. (Which occurs, validly; the spurious warning
has been removed).
filter selection: the 1.6 and earlier sum of absolute differences algorithm has
been reintroduced with an option to disfavor some filters over others where the
sums are close (not yet exposed). The selection code also logs the last known
occurence of each possible byte code across multiple lines. This allows
detection of PNG images with lower bit depth than the format implies and,
therefore, allows the filtering to be turned off in those cases as well.
The default write zlib settings are still lower than libpng16. The selection
algorithm is being refined (the overall results are worse than not doing any
filtering).
Signed-off-by: John Bowler <jbowler@acm.org>
A debug() assert fired if windowBits was set to 8 for the Huffman only and
no-compression cases. This commit changes it to do some extra checking. Remove
unreachable code in pz_default_settings, eliminate a spurious warning in pngcp
for small files.
Signed-off-by: John Bowler <jbowler@acm.org>
Implemented better defaulting of zlib settings based on image properties.
Implemented pass-through of png_write_rows when the rows can be used directly (a
common case) optimizing the handling of previous-row buffering.
Removed the METHODICAL filter selection method and disabled the HEURISTIC one;
the first was ridiculously slow (though useful for experiments) the second
doesn't work. Filter selection is temporarily disabled (it defaults to the
lowest numbered filter in the list; typically 'none').
New handling of compression settings (incomplete), new PNG compression level
(not yet visible in an API).
Back ported 'PNG_FAST_FILTERS' from 1.6 (in png.h).
There are minimal API changes beyond removal of the selection options. Work is
still to be done to investigate a filter selection mechanism that is at least as
good as the previous one.
Signed-off-by: John Bowler <jbowler@acm.org>
Output results during the search; not a perfect implementation but sufficient
for basic tests on zlib parameters.
Signed-off-by: John Bowler <jbowler@acm.org>
Some refinements for the search option and better (more consistent) reporting of
the results plus changes so that when compiled against libpng 1.6 the program
correctly copies text chunks; previously when a search option caused multiple
copies of the same file the copies after the first would not have the text
chunks.
Signed-off-by: John Bowler <jbowler@acm.org>
The internal read code change to stop sharing the palette was incompletely
implemented. The result is that unless palette index checking is turned off and
there are no read transformations the png_info palette gets deleted when the
png_struct is deleted. This is normally harmless (png_info gets deleted first)
but in the case of pngcp it results in use-after-free of the palette and,
therefore, palette corruption and maybe on some operating systems and access
violation.
This also updated pngcp 'search' mode to check a restricted range of memLevels;
there is an unrelated bug which means that lower zlib memLevels result in memory
corruption under some circumstances, probably less often than 1:1000.
Signed-off-by: John Bowler <jbowler@acm.org>
Also change the order of the 'level' and 'windowBits' searches to seach
windowBits first; this favours windowBits optimizations over compression level
ones on the basis that the latter should only affect the write code.
Signed-off-by: John Bowler <jbowler@acm.org>
This is still a work-in-progress but it seems fairly stable (if not exactly 100%
optimal). pngcp now allows 'all' for some options which iterates through all
possible settings (this reliably produces the smallest IDAT that libpng can
produce with those settings.) It also contains a --search command line option
which attempts to optimize this by skipping pointless tests; it is close, most
of the time, but not perfect.
Signed-off-by: John Bowler <jbowler@acm.org>
This adds code to iterate through the command line options when non-list options
have the 'all' parameter. Used to rapidly test the effect of different zlib
options.
Signed-off-by: John Bowler <jbowler@acm.org>
Also add an example program, pngcp.c, which illustrates the problem when used to
copy pngtest.png (the result is an invalid PNG because the tIME chunk is
duplicated.)
Signed-off-by: John Bowler <jbowler@acm.org>
