mscale -xysize 2400 3000 image.pgm | pamditherbw -hilbert |  \
      pamtopnm | pnmtops -scale 0.25 &gt; image.ps 
</pre>

<P>All options can be abbreviated to their shortest unique prefix.

<A NAME="lbAF">&nbsp;</A>
<H2>REFERENCES</H2>

<p>The only reference you need for this stuff is &quot;Digital
Halftoning&quot; by Robert Ulichney, MIT Press, ISBN 0-262-21009-6.

<P>The Hilbert curve space filling method is taken from &quot;Digital
Halftoning with Space Filling Curves&quot; by Luiz Velho, Computer
Graph