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 max­
       val.   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-per-sample  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.


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