til Netpbm 10.20
(January 2004), <b>pamcomp</b>'s predecessor <b>pnmcomp</b> always
treated the PPM samples as intensity-proportional even though they
were not, and drew few complaints.  So using <b>-linear</b> as a lie
is a reasonable thing to do if speed is important to you.

<p>Another technique to consider is to convert your PNM image to the
linear variation with <b>pnmgamma</b>, run <b>pamcomp</b> on it and
other transformations that like linear PNM, and then convert it back
to true PNM with <b>pnmgamm