P_NOTSET         1646 pngread.c         if (encoding == P_NOTSET) /* must be the file encoding */
P_NOTSET         1734 pngread.c            if (display->file_encoding == P_NOTSET)
P_NOTSET         2053 pngread.c         unsigned int data_encoding = P_NOTSET; /* Encoding libpng must produce */