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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 3.3//EN">
<html><head><title>Xwdtopnm User Manual</title></head>
<body>
<h1>xwdtopnm</h1>
Updated: 08 January 2010
<br>
<a href="#index">Table Of Contents</a>
<h2>NAME</h2>
xwdtopnm - convert an X11 or X10 window dump file to a PNM image
<h2 id="synopsis">SYNOPSIS</h2>
<b>xwdtopnm</b>
[<b>-verbose</b>]
[<b>-headerdump</b>]
[<i>xwdfile</i>]
<h2 id="description">DESCRIPTION</h2>
<p>This program is part of <a href="index.html">Netpbm</a>.
<p><b>xwdtopnm</b> reads an X11 or X10 window dump file as input and
produces a PNM image as output. The type of the output image depends
on the input file - if it's black and white, the output is PBM. If
it's grayscale, the output is PGM. Otherwise, it's PPM. The program
tells you which type it is writing.
<p>Using this program, you can convert anything you can display on an
X workstation's screen into a PNM image. Just display whatever you're
interested in, run the <b>xwd</b> program to capture the contents of
the window, run it through <b>xwdtopnm</b>, and then use <b>pamcut</b>
to select the part you want.
<p>Note that a pseudocolor XWD image (typically what you get when you
make a dump of a pseudocolor X window) has maxval 65535, which means
the PNM file that <b>xwdtopnm</b> generates has maxval 65535. Many
older image processing programs (that aren't part of the Netpbm
package and don't use the Netpbm programming library) don't know how
to handle a PNM image with maxval greater than 255 (because there are
two bytes instead of one for each sample in the image). So you may
want to run the output of <b>xwdtopnm</b> through <b>pamdepth</b>
before feeding it to one of these old programs.
<p><b>xwdtopnm</b> can't convert every kind of XWD image (which essentially
means it can't convert an XWD created from every kind of X display
configuration). In particular, it cannot convert one with more than 24 bits
per pixel.
<h2 id="options">OPTIONS</h2>
<p>In addition to the options common to all programs based on libnetpbm
(most notably <b>-quiet</b>, see <a href="index.html#commonoptions">
Common Options</a>), <b>xwdtopnm</b> recognizes the following
command line options:
<dl>
<dt><b>-verbose</b>
<dd>This option causes <b>xwdtopnm</b> to display handy information about the
input image and the conversion process
<dt><b>-headerdump</b>
<dd>This option causes <b>xwdtopnm</b> to display the contents of the
X11 header. It has no effect when the input is X10. This option was
new in Netpbm 10.26 (December 2004).
</dl>
<h2 id="notes">NOTES</h2>
<h3 id="twobytesamples">Two Byte Samples</h3>
<p><b>xwdtopnm</b> sometimes produces output with a maxval greater than 255,
which means the maximum value of a sample (one intensity value, e.g. the
red component of a pixel) is greater than 255 and therefore each sample
takes 2 bytes to represent. This can be a problem because some programs
expect those bytes in a different order from what the Netpbm format specs
say, which is what <b>xwdtopnm</b> produces, which means they will see totally
different colors than they should. <b>xv</b> is one such program.
<p>If this is a problem (e.g. you want to look at the output of <b>xwdtopnm</b>
with <b>xv</b>), there are two ways to fix it:
<ul>
<li>Pass the output through <b>pamendian</b> to produce the format the
program expects.
<li>Pass the output through <b>pamdepth</b> to reduce the maxval below 256
so there is only one byte per sample.
</ul>
<p>Often, there is no good reason to have a maxval greater than 255. It
happens because in XWD, but not PNM, each color component of a pixel can have
different resolution, for example 5 bits for blue (maxval 31), 5 bits for red
(maxval 31), and 6 bits for green (maxval 63), for a total of 16 bits per
pixel. In order to reproduce the colors as closely as possible,
<b>xwdtopnm</b> has to use a large maxval. In this example, it would use
31 * 63 = 1953, and use 48 bits per pixel.
<p>Because this is a common and frustrating problem when using <b>xwdtopnm</b>,
the program issues a warning whenever it generates output with two byte
samples. You can quiet this warning with the <b>-quiet</b> <a href="index.html#commonoptions">common option</a>. The warning was new in Netpbm 10.46
(March 2009).
<h2 id="seealso">SEE ALSO</h2>
<a href="pnmtoxwd.html">pnmtoxwd</a>,
<a href="pamendian.html">pamendian</a>,
<a href="pamdepth.html">pamdepth</a>,
<a href="pnm.html">pnm</a>,
<b>xwd</b> man page
<h2 id="author">AUTHOR</h2>
Copyright (C) 1989, 1991 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="#notes">NOTES</a>
<ul>
<li><a href="#twobytesamples">Two Byte Samples</a>
</ul>
<li><a href="#seealso">SEE ALSO</a>
<li><a href="#author">AUTHOR</a>
</ul>
</body>
</html>
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