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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 3.2//EN">
<HTML><HEAD><TITLE>Pbmmask User Manual</TITLE></HEAD>
<BODY>
<H1>pbmmask</H1>
Updated: 08 August 1989
<BR>
<A HREF="#index">Table Of Contents</A>

<A NAME="lbAB">&nbsp;</A>
<H2>NAME</H2>

pbmmask - create a mask bitmap from a regular bitmap

<A NAME="lbAC">&nbsp;</A>
<H2>SYNOPSIS</H2>

<B>pbmmask</B>
[<B>-expand</B>]
[<I>pbmfile</I>]

<A NAME="lbAD">&nbsp;</A>
<H2>DESCRIPTION</H2>

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

<p><b>pbmmask</b> reads a PBM image as input and Generates a
corresponding mask of the foreground areas as another PBM image.

<P>The color to be interpreted as &quot;background&quot; is
determined automatically.  Regardless of which color is background,
the mask will be white where the background is and black where the
figure is.

<P>This lets you do a masked paste like this, for objects with a black
background:

<PRE>
    pbmmask obj &gt; objmask
    pnmpaste &lt; dest -and objmask &lt;x&gt; &lt;y&gt; | pnmpaste -or obj &lt;x&gt; &lt;y&gt;
</PRE>

For objects with a white background, you can either invert them or
add a step:
<PRE>
    pbmmask obj &gt; objmask
    pnminvert objmask | pnmpaste -and obj 0 0 &gt; blackback
    pnmpaste &lt; dest -and objmask &lt;x&gt; &lt;y&gt; | pnmpaste -or blackback &lt;x&gt; &lt;y&gt;
</PRE>

Note that this three-step version works for objects with black backgrounds
too, if you don't care about the wasted time.

<P>You can also use masks with grayscale and color images, using the
<I>pnmarith</I> tool.  For instance:

<PRE>
    ppmtopgm obj.ppm | pamditherbw -threshold | pbmmask &gt; objmask.pbm
    pnmarith -multiply dest.ppm objmask.pbm &gt; t1.ppm
    pnminvert objmask.pbm | pnmarith -multiply obj.ppm - &gt; t2.ppm
    pnmarith -add t1.ppm t2.ppm
</PRE>

An interesting variation on this is to pipe the mask through
<I>pnmsmooth</I> before using it.  This makes the boundary between the
two images less sharp.

<A NAME="lbAE">&nbsp;</A>
<H2>OPTIONS</H2>

<DL COMPACT>
<DT><B>-expand</B>

<DD>Expands the mask by one pixel out from the image.  This is useful
if you want a little white border around your image.  (A better
solution might be to turn the <b>pbmlife</b> program into a general
cellular automaton tool...)

</DL>

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

<B><A HREF="ppmcolormask.html">ppmcolormask</A></B>,
<B><A HREF="pnmpaste.html">pnmpaste</A></B>,
<B><A HREF="pnminvert.html">pnminvert</A></B>,
<B><A HREF="pnmarith.html">pnmarith</A></B>,
<B><A HREF="pnmsmooth.html">pnmsmooth</A></B>
<B><A HREF="pbm.html">pbm</A></B>,

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

Copyright (C) 1988 by Jef Poskanzer.

<HR>
<A NAME="index">&nbsp;</A>
<H2>Table Of Contents</H2>
<UL>
<LI><A HREF="#lbAB">NAME</A>
<LI><A HREF="#lbAC">SYNOPSIS</A>
<LI><A HREF="#lbAD">DESCRIPTION</A>
<LI><A HREF="#lbAE">OPTIONS</A>
<LI><A HREF="#lbAF">SEE ALSO</A>
<LI><A HREF="#lbAG">AUTHOR</A>
</UL>
</BODY>
</HTML>