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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 3.3//EN">
<html><head><title>Pgmdeshadow User Manual</title></head>
<body>
<h1>pgmdeshadow</h1>
Updated: 06 July 2006
<br>
<a href="#index">Table Of Contents</a>
<h2>NAME</h2>
pgmdeshadow - Deshadow a PGM image
<h2 id="synopsis">SYNOPSIS</h2>
<b>pgmdeshadow</b>
[<i>pnmfile</i>]
<h2 id="description">DESCRIPTION</h2>
<p>This program is part of <a href="index.html">Netpbm</a>.
<p><b>pgmdeshadow</b> removes gray shadows from an image. This is
useful for an image containing text, such as a scanned book pages,
where a shadow typically appears near the book crease or near one side
of the image. <b>pgmdeshadow</b> recognizes a gray shadow as an area
of smoothly changing color, starting from the outer edges of the
image. The program uses a simple image reconstruction algorithm to
determine the local shadow gray level, then divides each pixel's gray
level by the local shadow gray level.
<p>The algorithm is the "fast hybrid grayscale reruction"
algorithm from Luc Vincent, "Morphological Grayscale Reruction in
Image Analysis: Applications and Efficient Algorithms.
<h2 id="options">OPTIONS</h2>
<p>There are no command line options defined specifically
for <b>pgmdeshadow</b>, but it recognizes the options common to all
programs based on libnetpbm (See <a href="index.html#commonoptions">
Common Options</a>.)
<h2 id="references">REFERENCES</h2>
<ul>
<li>Luc Vincent, "Morphological Grayscale Reconstruction in Image
Analysis: Applications and Efficient Algorithms," IEEE
Transactions on Image Processing, vol. 2, no. 2, April 1993,
pp. 176-201.
</ul>
<h2 id="seealso">SEE ALSO</h2>
<a href="ppmshadow.html">ppmshadow</a>,
<a href="pgm.html">pgm</a>
<h2 id="history">HISTORY</h2>
<p><b>pgmdeshadow</b> was added to Netpbm in Version 10.35 (August 2006).
<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="#references">REFERENCES</a>
<li><a href="#seealso">SEE ALSO</a>
<li><a href="#history">HISTORY</a>
</ul>
</body>
</html>
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