pnmdepth(1)
NAME
pnmdepth - change the maxval in a portable anymap
SYNOPSIS
pnmdepth newmaxval [pnmfile]
DESCRIPTION
Reads a portable anymap as input. Scales all the pixel values, and
writes out the image with the new maxval. Scaling the colors down to a
smaller maxval will result in some loss of information.
Be careful of off-by-one errors when choosing the new maxval. For
instance, if you want the color values to be five bits wide, use a maxval of 31, not 32.
One important use of pnmdepth is to convert a new format 2-byte-persample PNM file to the older 1-byte-per-sample format. Before April
2000, essentially all raw (binary) format PNM files had a maxval less
than 256 and one byte per sample, and many programs may rely on that.
If you specify a newmaxval less than 256, the resulting file should be
readable by any program that worked with PNM files before April 2000.
SEE ALSO
pnm(5), ppmquant(1), ppmdither(1)
AUTHOR
- Copyright (C) 1989, 1991 by Jef Poskanzer.