ppmtoyuvsplit - convert a portable pixmap into 3 subsampled raw YUV files
Reads a portable pixmap as input. Produces 3 raw files
basename.Y, basename.U and basename.V as output. These files
are the subsampled raw YUV representation of the input
pixmap, as required by the Stanford MPEG codec. The
subsampling is done by arithmetic mean of 4 pixels colors
into one. The YUV values are scaled according to CCIR.601,
as assumed by MPEG.
Copyright (C) 1993 by Andre Beck.
Based on ppmtoyuv.c