wever, <b>pamditherbw</b> doesn't check, so if you feed
it e.g. a PPM image, it will produce arbitrary results (actually, it
just takes the first channel of whatever you give it and treats it as
if it represented gray levels).

<p>The output is a PAM with tuple type BLACKANDWHITE.  You can turn
this into a PBM (if you need to use it with an older program doesn't
understand PAM) with <b>pamtopnm</b>.

<P>To do the opposite of dithering, you can usually just scale the image
down and then back up again with <b