riginal image times inverse mask.

<DT><B>shadback.ppm</B>
<DD>
Generated shadow times positive mask

<DT><B>allbutfg.ppm</b>
<dd>
Everything but the foreground (foreground area is black).

</DL>

<A NAME="lbAG">&nbsp;</A>
<H2>LIMITATIONS</H2>

<p>The source image must contain sufficient space on the edges in the
direction in which the shadow is cast to contain the shadow -- if it
doesn't some of the internal steps may fail.  You can usually expand
the border of a too-tightly-cropped image with <B>pnmmargin