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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 3.2//EN">
<HTML><HEAD><TITLE>Pbmreduce User Manual</TITLE></HEAD>
<BODY>
<H1>pbmreduce</H1>
Updated: 02 August 1989
<BR>
<A HREF="#index">Table Of Contents</A>

<H2>NAME</H2>

pbmreduce - read a PBM image and reduce it N times

<H2 id="synopsis">SYNOPSIS</H2>

<B>pbmreduce</B>
[<B>-floyd</B>|<B>-fs</B>|<B>-threshold</B>]
[<B>-value</B> <I>val</I>] <I>N</I>
[<I>pbmfile</I>]

<P>You can abbreviate any option to its shortest unique prefix.

<H2 id="description">DESCRIPTION</H2>

<p>This program is part of <a href="index.html">Netpbm</a>.

<p><b>pbmreduce</b> reads a PBM image as input and reduces it by a
factor of <I>N</I>, producing a PBM image as output.

<P><b>pbmreduce</b> duplicates a lot of the functionality of
<b>pamditherbw</b>; you could do something like <tt>pamscale |
pamditherbw</tt>, but <b>pbmreduce</b> is a lot faster.

<P>You can use <B>pbmreduce</B> to &quot;re-halftone&quot; an image.
Let's say you have a scanner that only produces black&amp;white, not
grayscale, and it does a terrible job of halftoning (most b&amp;w
scanners fit this description).  One way to fix the halftoning is to
scan at the highest possible resolution, say 300 dpi, and then reduce
by a factor of three or so using <b>pbmreduce</b>.  You can even
correct the brightness of an image, by using the <B>-value</B> option.

<H2 id="options">OPTIONS</H2>

<P>By default, <b>pbmreduce</b> does the halftoning after the
reduction via boustrophedonic Floyd-Steinberg error diffusion;
however, you can use the <B>-threshold</B> option to specify simple
thresholding.  This gives better results when reducing line drawings.

<P>The <B>-value</B> option alters the thresholding value for all
quantizations.  It should be a real number between 0 and 1.  Above 0.5
means darker images; below 0.5 means lighter.

<H2 id="seealso">SEE ALSO</H2>

<A HREF="pamenlarge.html">pamenlarge</A>,
<A HREF="pamscale.html">pamscale</A>,
<A HREF="pamditherbw.html">pamditherbw</A>,
<A HREF="pbm.html">pbm</A>

<H2 id="author">AUTHOR</H2>

Copyright (C) 1988 by Jef Poskanzer.

<HR>
<H2 id="index">Table Of Contents</H2>
<UL>
<LI><A HREF="#synopsis">SYNOPSIS</A>
<LI><A HREF="#description">DESCRIPTION</A>
<LI><A HREF="#options">OPTIONS</A>
<LI><A HREF="#seealso">SEE ALSO</A>
<LI><A HREF="#author">AUTHOR</A>
</UL>
</BODY>
</HTML>