hat
are not linearly proportional to intensity.  So <b>pamcomp</b>, by
default, performs a calculation on each sample read from its input and
each sample written to its output to convert between these
gamma-adjusted numbers and internal intensity-proportional numbers.

<p>Sometimes you are not working with true PNM or PAM images, but
rather a variation in which the sample values are in fact directly
proportional to intensity.  If so, use the <b>-linear</b> option to
tell <b>pamcomp</b> this.  <b>pamcomp</B>