g image subtracted from it.  In either
case, <b>pamcomp</b> clips the resulting color component intensities
so they are nonnegative and don't exceed the output image's maxval.

<p>This may seem like a strange thing to do, but it has uses.  You
can use it to brighten or darken or saturate or desaturate areas of the
underlaying image.  See <a href="extendedopacity.html">
this description</a> of the technique.
     
<p>This option was added in Netpbm 10.6 (July 2002).  Before Netpbm 10.15
(April 2003), values 