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Write code update

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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>
This commit is contained in:
John Bowler
2016-05-04 17:02:20 -07:00
parent 1fd42d849d
commit cde9b583a8
10 changed files with 1834 additions and 1330 deletions
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43
png.h
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@@ -1690,25 +1690,14 @@ PNG_EXPORT(66, void, png_set_crc_action, (png_structrp png_ptr, int crit_action,
* ignored if SUB is set; this is because these filter pairs are equivalent
* when there is no previous row.
*
* 2) PNG_SELECT_FILTER_METHODICALLY_SUPPORTED:
* If SELECT_FILTER_METHODICALLY is 'on' libpng tries all the filters in the
* list and selects the one which gives the shortest compressed row, favoring
* earlier filters.
* 2) PNG_SELECT_FILTER_SUPPORTED:
* libpng will buffer rows until enough data is available to perform a
* reasonable filter selection heuristic then select filters for at least the
* first buffered row.
*
* 3) PNG_SELECT_FILTER_HEURISTICALLY_SUPPORTED:
* If SELECT_FILTER_HEURISTICALLY is 'on' libpng tests the start of each row
* (a few thousand bytes at most) to see which filter is likely to produce
* best compression.
*
* 4) If neither (2) nor (3) libpng selects the first filter in the list (there
* is no warning that this will happen - check the #defines if you need to
* know.)
*
* The seletion options are turned 'on' using png_set_option(method,
* PNG_OPTION_ON) and turned off with PNG_OPTION_OFF. If a selection method is
* turned off it will never be used, if neither option is turned on or off (i.e.
* if png_set_option is not called) the first supported option (2) or (3) will
* be used.
* 3) !PNG_SELECT_FILTER_SUPPORTED:
* libpng selects the first filter in the list (there is no warning that this
* will happen - check the #defines if you need to know.)
*
* If you intend to use 'previous row' filters in an image set either the UP or
* PAETH filter before the first call to png_write_row, depending on whether you
@@ -1717,12 +1706,6 @@ PNG_EXPORT(66, void, png_set_crc_action, (png_structrp png_ptr, int crit_action,
* You can also select AVG on the first row; it uses half the value of the
* preceding byte as a predictor and is not likely to have very good
* performance.
*
* The SELECT_FILTER_METHODICALLY option is slow and memory intensive, but it is
* almost certain to produce the smallest PNG file. Depending on the image data
* the HEURISTIC option may improve results significantly over the NONE filter
* and it has little overall effect on compression speed, however it can
* sometimes produce larger files than not using any filtering.
*/
PNG_EXPORT(67, void, png_set_filter, (png_structrp png_ptr, int method,
int filters));
@@ -1752,12 +1735,12 @@ PNG_EXPORT(67, void, png_set_filter, (png_structrp png_ptr, int method,
#define PNG_FILTER_AVG PNG_FILTER_MASK(PNG_FILTER_VALUE_AVG)
#define PNG_FILTER_PAETH PNG_FILTER_MASK(PNG_FILTER_VALUE_PAETH)
/* Then two convenience values. PNG_NO_FILTERS is the same as
/* Then three convenience values. PNG_NO_FILTERS is the same as
* PNG_FILTER_VALUE_NONE, but this is harmless because they mean the same thing.
*/
#define PNG_NO_FILTERS 0x00
#define PNG_ALL_FILTERS (PNG_FILTER_NONE | PNG_FILTER_SUB | PNG_FILTER_UP | \
PNG_FILTER_AVG | PNG_FILTER_PAETH)
#define PNG_NO_FILTERS 0x00
#define PNG_FAST_FILTERS (PNG_FILTER_NONE | PNG_FILTER_SUB | PNG_FILTER_UP)
#define PNG_ALL_FILTERS (PNG_FAST_FILTERS | PNG_FILTER_AVG | PNG_FILTER_PAETH)
#ifdef PNG_WRITE_SUPPORTED
#ifdef PNG_WRITE_WEIGHTED_FILTER_SUPPORTED /* DEPRECATED */
@@ -3629,9 +3612,7 @@ PNG_EXPORT(245, int, png_image_write_to_memory, (png_imagep image, void *memory,
#define PNG_EXTENSIONS 0 /* BOTH: enable or disable extensions */
#define PNG_MAXIMUM_INFLATE_WINDOW 2 /* SOFTWARE: force maximum window */
#define PNG_SKIP_sRGB_CHECK_PROFILE 4 /* SOFTWARE: Check ICC profile for sRGB */
#define PNG_SELECT_FILTER_HEURISTICALLY 6 /* SOFTWARE: see png_set_filter */
#define PNG_SELECT_FILTER_METHODICALLY 8 /* SOFTWARE: see png_set_filter */
#define PNG_OPTION_NEXT 10 /* Next option - numbers must be even */
#define PNG_OPTION_NEXT 6 /* Next option - numbers must be even */
/* Return values: NOTE: there are four values and 'off' is *not* zero */
#define PNG_OPTION_UNSET 0 /* Unset - defaults to off */