An 8-bit PCX file whose image data is followed by the palette marker
(0x0C) and fewer than 768 color bytes was read as gray levels. The reader
now notes where the run-length encoded image data ends, and when the
palette marker follows it without all 768 colors, refuses the file as cut
short. An 8-bit file with nothing after its image data still reads as
gray levels, and a gray level of 12 that falls 769 bytes before the end of
such a file is read as a pixel instead of as the palette marker.