libpng/KNOWNBUG

Known bugs and suggested enhancements in libpng-1.0.4


1. March 15, 1998 -- OPTIMIZATION -- Kevin Bracey

   Loops need to be optimized everywhere

   Make them count down instead of up -- Kevin Bracey

   Optimizing compilers don't need this, and making
   the change would be error prone -- Tom Lane, Glenn R-P

   Question whether i-- or --i is better.

   STATUS: Under investigation, postponed until after
   libpng-1.0.5.  About 160 loops will be turned around
   in libpng-1.0.Nn, for testing.

2. July 4, 1998 -- ENHANCEMENT -- Glenn R-P

   libpng-1.0.5 and earlier transform colors to gamma=1.0 space for
   merging with background, and then back to the image's gamma.  The
   bit_depth of the intermediate (gamma=1.0) representation is probably
   not sufficient.  In the typical gamma=1/2.2 situation, the linear
   pixels need about 4 more bits than the gamma-encoded ones, to avoid
   loss of precision.  A similar situation exists with the rgb_to_gray
   operation.

   STATUS: under development.

3. September 1999 -- ENHANCEMENT --

   It should be possible to use libpng without floating-point aritmetic.

   STATUS: Under investigation, implementation postponed until after
   libpng-1.0.5.  The application interface will change because replacements
   for the png_set_gAMA(), png_set_cHRM(), and corresponding png_get_()
   functions will be needed.

4. September 1999 -- BUG --

   Portions of the new MMX code in pngvcrd.c are defined out because the
   did not work properly.  When PNGVCRD_INTERLACE_BUG_IS_FIXED is defined,
   to enable the code, pngtest pngtest.png pngout.png results in a
   "Debug error! Damage before normal block # 57 at 0x007e19f0" on
   a Pentium II with MMX system.  This seems to be caused by the heap
   being trashed before a free() in png_read_destroy().

   When PNGVCRD_COMBINE_BUG_IS_FIXED is defined (what?)