Signed-off-by: NJohn Bowler <jbowler@acm.org>

This reverts commit 9517f7b6.

inadvertently replaced with libpng17 versions).

attempts to ignore the errors in the code aren't quite enough to
deal with the 'channel selection' encoding added to libpng 1.7; abort.

The previous attempts to ignore the errors in the code aren't quite enough to
deal with the 'channel selection' encoding added to libpng 1.7; abort.
pngvalid.c is changed to drop this encoding in prior versions.
Signed-off-by: NJohn Bowler <jbowler@acm.org>

Signed-off-by: NJohn Bowler <jbowler@acm.org>

Signed-off-by: NJohn Bowler <jbowler@acm.org>

Remove the '--strict' in 1.6 because of the double-gamma-correction warning,
update pngstest-errors.h for the errors detected with the new contrib/testspngs
PNG test files.
Signed-off-by: NJohn Bowler <jbowler@acm.org>

Back ported from libpng 1.7
Signed-off-by: NJohn Bowler <jbowler@acm.org>

tests/pngstest-* are changed so that the new test files are divided into 8
groups by gamma and alpha channel.  This makes each test take just under 5
seconds on a moderately up-to-date x86_64 system using libpng16 (test times are
somewhat variable under libpng17 at present because of the lack of optimization
in some gamma processing paths.)

These tests have considerably better code and pixel-value coverage than
contrib/pngsuite however coverage is still incomplete.
Signed-off-by: NJohn Bowler <jbowler@acm.org>

functions. They unnecessarily duplicate png_set_filler() and png_set_add_alpha()
which now work properly with 16-bit images.

input that was made in version 1.6.17beta01, to preserve legacy
behavior even though it was incorrect.  Instead, added new API
png_set_filter_16() and png_set_add_alpha_16() that set a flag to
make png_do_read_filter() interpret the filler bytes properly.

This update incorporates errors resulting from the more extensive image test
suite used in libpng 1.7
Signed-off-by: NJohn Bowler <jbowler@acm.org>

Splitting the machine generated error structs out to a file allows the values to
be updated without changing pngstest.c itself, since libpng 1.6 and 1.7 have
slightly different error limits this simplifies maintenance.
Signed-off-by: NJohn Bowler <jbowler@acm.org>

This is a patch for libpng16.
It incorporates fixes to the low-bit-depth gray background handling from
libpng17 and turns one of the low-bit-depth gray cases that does work (and,
indeed, did work before) in libpng16
Signed-off-by: NJohn Bowler <jbowler@acm.org>

This updates libpng16 with all the test changes from libpng17,
including changes to pngvalid.c to ensure that the original,
distributed, version of contrib/visupng/cexcept.h can be used.

pngvalid contains the correction to the use of SAVE/STORE_
UNKNOWN_CHUNKS; a bug revealed by changes in libpng 1.7.  More
tests contain the --strict option to detect warnings and the
pngvalid-standard test has been corrected so that it does not
turn on progresive-read (there is a separate test which does
that.)

Some signed/unsigned fixes have been made.
Signed-off-by: NJohn Bowler <jbowler@acm.org>