PNG_FREE_HIST     597 png.c             if ((mask & PNG_FREE_HIST)  & info_ptr->free_me)
PNG_FREE_HIST     181 pngset.c          png_free_data(png_ptr, info_ptr, PNG_FREE_HIST, 0);
PNG_FREE_HIST     195 pngset.c          info_ptr->free_me |= PNG_FREE_HIST;