PNG_FILTER_VALUE_SUB  241 libavcodec/pngdec.c     case PNG_FILTER_VALUE_SUB:
PNG_FILTER_VALUE_SUB  145 libavcodec/pngenc.c     case PNG_FILTER_VALUE_SUB:
PNG_FILTER_VALUE_SUB  171 libavcodec/pngenc.c         pred = PNG_FILTER_VALUE_SUB;