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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 3.3//EN">
<html><head><title>Pnmcat User Manual</title></head>
<body>
<h1>pnmcat</h1>
Updated: 30 July 2022
<h2>NAME</h2>
pnmcat - replaced by pamcat
<h2>DESCRIPTION</h2>
<p>This program is part of <a href="index.html">Netpbm</a>.
<p><b>pnmcat</b> was obsoleted by <a href="pamcat.html"><b>pamcat</b></a>,
introduced with Netpbm 11.00 (September 2022). <b>pamcat</b> is almost
backward compatible with <b>pnmcat</b>, plus adds many additional functions,
including the ability to process PAM images.
<p>These are the ways in which <b>pamcat</b> is not backward compatible with
<b>pnmcat</b>:
<ul>
<li><b>pamcat</b> produces PAM output, whereas <b>pnmcat</b> produces PNM.
With <b>pamcat</b>, If your inputs are PNM and you want PNM output, you
can run the output through <b>pamtopnm</b>. But most Netpbm programs
that take PNM input can just as well take the PAM input, so this may not
be necessary.
<li><b>pnmcat</b> recognizes PBM, PGM, and PPM input images as visual
images and makes sure the images are the same in the concatenated
outputs even though the output may be a different format. For example,
if you are concatenating PBM image foo.pbm and PPM image bar.ppm, the
resulting image will be PPM and the foo part of it will have the same
black and white pixels as the foo.pbm input.
<p><b>pamcat</b>, on the other hand, work on generic PAM images and does
not really recognize colors. It sees a PBM input as a 1-plane image
and a PPM input as a 3-plane image and produces a 3-plane output
image. By default, in the example above, the foo part of the output
contains the black and white sample values in its first plane, but
zeroes in its second and third planes, which means if you take the
output image to be a PPM-like color visual image, the foo part is
black and red instead of black and white.
<p>But this is easy to fix. Use the <b>-extendplane</b> option to say
instead of making those additional planes zero, make them copies of
the first plane. So the three panes in the foo part of the output
image will all contain the same sample values as the single plane of
the PBM input, which means if you use the output image as a color
image, those pixels are black and white.
</ul>
<p>For full backward compatibility, <b>pnmcat</b> remains in Netpbm,
implemented as a simple wrapper of <b>pamcat</b>. For the fewest problems
with future releases of Netpbm, you should not use <b>pnmcat</b> in any
new work.
<h2>Using pnmcat in old Netpbm</h2>
<p>In Netpbm before 11.00, use the manual for <b>pamcat</b> with
<b>pnmcat</b>, observing the following differences:
<ul>
<li><b>pnmcat</b> accepts only PNM input (i.e. PBM, PGM, or PPM)
and produces only PNM output. The output is the highest format
(PBM, PGM, PPM) of any of its inputs.
<li>Features that the manual says were added to <b>pamcat</b>
in Release 11.00 or later are not there.
</ul>
</body>
</html>
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