libpng/KNOWNBUG

Known bugs and suggested enhancements in libpng-1.0.6

1. April 23, 2000 -- BUG -- binary incompatibility

   Libpng-1.0.6 introduced binary incompatibility for applications that
   make direct access to the info_ptr and png_ptr, due to the insertion
   of the free_me member ahead of some previously existing members.

   STATUS:  Fixed in libpng-1.0.6g

2. April 15, 2000 -- BUG -- pnggccrd.c

   If PNG_NO_GLOBAL_ARRAYS is defined, pnggccrd.c will not compile.

   STATUS: Fixed in libpng-1.0.6g

3. April 1, 2000 -- BUG

   Under some circumstances old applications that make direct access to
   the info_ptr->text and its members might free the same memory that
   is also free'ed by libpng during the png_destroy_struct process.

   Fixed in libpng-1.0.6-patch-c and libpng-1.0.6d.  The PNG_FREE_TEXT flag
   bit in info_ptr->free_me is now checked to make sure libpng is responsible
   for freeing the memory.

4. April 1, 2000 -- BUG

   The non-ISO-C "strdup()" function is used in png.c

   STATUS: The function has been simplified and no longer uses strdup()
   in libpng-1.0.6-patch-c and libpng-1.0.6d.

5. March 24, 2000 -- BUG

   The png_set_rgb_to_gray_fixed() function is setting incorrect weighting
   factors.

   STATUS: Fixed in libpng-1.0.6-patch-b and libpng-1.0.6d.

6. March 22, 2000 -- BUG

   There are some printf() and fprintf() statements active in pngwutil.c
   when PNG_NO_STDIO and PNG_sCAL_SUPPORTED are both defined.

   STATUS: Fixed in libpng-1.0.6-patch-a and libpng-1.0.6d.  The strcpy()
   function is used instead.

7. March 22, 2000 -- BUG

   The length of the iCCP chunk data is calculated incorrectly; because
   it can contain zeroes, strlen() doesn't work.

   STATUS: Fixed in libpng-1.0.6-patch-a and libpng-1.0.6d by adding a
   data_length parameter to the png_decompress_chunk() function.

8. 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-1.1.0.  About 160 loops will be turned around
   in libpng-1.1.Nn, for testing.

9. 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.

10. September 1999 -- ENHANCEMENT --

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

   STATUS: Under investigation, implementation postponed until after
   libpng-1.0.6.  The application interface will change because replacements
   for the png_set_gAMA(), png_set_cHRM(), and corresponding png_get_()
   functions will be needed.

   Much of this was completed in libpng-1.0.6, but gamma compensation
   is not yet done in fixed-point arithmetic.