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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 3.3//EN">
<html><head><title>Pamdepth User Manual</title></head>
<body>
<h1>pamdepth</h1>
Updated: 26 August 2020
<br>
<a href="#index">Table Of Contents</a>
<h2>NAME</h2>
pamdepth - change the depth (color resolution) in a Netpbm image
<h2 id="synopsis">SYNOPSIS</h2>
<b>pamdepth</b> <i>newmaxval</i> [<i>netpbmfile</i>]
<h2 id="description">DESCRIPTION</h2>
<p>This program is part of <a href="index.html">Netpbm</a>.
<p><b>pamdepth</b> reads a Netpbm image as input, changes its depth (color
resolution), and writes out the resulting Netpbm image. I.e. the output has a
different maxval from the input, but all the same colors (apart from rounding
error).
<p>Reducing the depth results in some loss of information.
<p>Here is an example of the effect at the image format level: Assume you
start with an image with maxval 100 and sample values of 50 and 100. You
tell <b>pamdepth</b> to change it to depth 150. The output has maxval
200 and sample values 75 and 150.
<p>This program works on multi-image streams.
<p>Be careful of off-by-one errors when choosing the new maxval. For
instance, if you want the color values to be five bits wide, use a
maxval of 31, not 32.
<p>One important use of <b>pamdepth</b> is to convert a new format
2-byte-per-sample PNM file to the older 1-byte-per-sample format.
Before April 2000, essentially all raw (binary) format PNM files had a
maxval less than 256 and one byte per sample, and many programs may
rely on that. If you specify a <i>newmaxval</i> less than 256, the
resulting file should be readable by any program that worked with PNM
files before April 2000.
<h3 id="output_format">Output Format</h3>
<p>The output format (PBM, etc.) and, in the case of PAM, tuple type, of the
output is usually the same as the input.
<p>However, changing the depth of a black and white image does not make
sense, except to turn it into a grayscale image, so if the input is a black
and white image, <b>pamdepth</b> makes the output grayscale. To be more
precise, if the input is a PBM image, the output is PGM, and if the input
is a PAM with tuple type BLACK_AND_WHITE or BLACK_AND_WHITE_ALPHA, the
output is a PAM with tuple type GRAYSCALE or GRAYSCALE_ALPHA, respectively.
<p>This conversion happens even if the new maxval is 1.
<p>Before Netpbm 10.92 (September 2020), <b>pamdepth</b> failed if the input
was PAM with a black and white tuple type and the new maxval was anything but
1. But it always promoted PBM to PGM.
<h2 id="options">OPTIONS</h2>
<p>There are no command line options defined specifically
for <b>pamdepth</b>, but it recognizes the options common to all
programs based on libnetpbm (See <a href="index.html#commonoptions">
Common Options</a>.)
<h2 id="seealso">SEE ALSO</h2>
<a href="pnm.html">pnm</a>,
<a href="pam.html">pam</a>,
<a href="pnmquant.html">pnmquant</a>,
<a href="ppmdither.html">ppmdither</a>
<a href="pambrighten.html">pambrighten</a>
<a href="pamfunc.html">pamfunc</a>
<h2 id="history">HISTORY</h2>
<p><b>pamdepth</b> was new in Netpbm 10.32 (February 2006). It replaced
<b>pnmdepth</b>, by Jef Poskanzer. <b>pamdepth</b> is backward compatible
with <b>pnmdepth</b> and adds the ability to process arbitrary PAM images
and the ability to process multi-image input streams. <b>pnmdepth</b>
handled only PNM images and ignored all but the first in any stream.
<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="#history">HISTORY</a>
</ul>
</body>
</html>
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