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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 3.3//EN">
<html><head><title>Pambrighten User Manual</title></head>
<body>
<h1>pambrighten</h1>
Updated: 12 January 2019
<br>
<a href="#index">Table Of Contents</a>
<h2>NAME</h2>
pambrighten - change a PPM image's Saturation and Value
<h2 id="synopsis">SYNOPSIS</h2>
<b>pambrighten</b>
[<b>-saturation=</b>[<b>+</b>|<b>-</b><i>saturation_percent</i>]]
[<b>-value=</b>[<b>+</b>|<b>-</b><i>value_percent</i>]]
<i>netpbmfile</i>
<p>Minimum unique abbreviation of option is acceptable. You may use
double hyphens instead of single hyphen to denote options. You may use
white space in place of the equals sign to separate an option name
from its value.
<h2 id="description">DESCRIPTION</h2>
<p>This program is part of <a href="index.html">Netpbm</a>.
<p><b>pambrighten</b> increases or decreases the Saturation and Value
(from the HSV color space) of each pixel of a Netpbm image. You specify
the percentage change for each of those parameters.
<p>You can also remap the colors of the pixels so their Values cover the full
range of possible Values.
<p>The output format is the same as the input format and any extra channels,
such as transparency, are passed through.
<p>Hue-Saturation-Value, or HSV, is one way to represent a color, like the
more well-known RGB. Hue, Saturation, and Value are numbers in the range from
0 to 1. We always capitalize them in this document when we mean the number
from the HSV color space, especially since "value" as a conventional English
word has a much more abstract meaning.
<p>Value is a measure of how bright the color is, relative to some specified
maximum (the Netpbm formats are also defined in terms of a specified maximum
brightness -- For the purposes of this program, they are the same). In
particular, it is the brightness of the brightest primary color component of
the color divided by the maximum brightness possible for a component. Zero
Value means black. White has full Value.
<p>Hue is an indication of the secondary color with the same brightness that
most closely approximates the color. A secondary color is made of a
combination of at most two of the primary colors.
<p>Saturation is a measure of how close the color is to the color indicated by
the Hue and Value. A lower number means more light of the third primary color
must be added to get the exact color. Full Saturation means the color is a
secondary color. Zero Saturation means the color is gray (or black or white).
Decreasing the saturation of a color tends to make it washed out.
<p>If it is impossible to increase the Value of a pixel by the amount you
specify (e.g. the Value is .5 and you specify +200%), <b>pambrighten</b>
increases it to full Value instead.
<p>If it is impossible to increase the Saturation of a pixel by the amount
you specify (e.g. it is already half saturated and you specify +200%),
<b>pambrighten</b> increases it to full Saturation instead.
<p>For a simpler kind of brightening, you can use <b>pamfunc -multiplier</b>
simply to increase the brightness of each pixel by a specified percentage,
clipping each RGB component where the calculated brightness would exceed full
brightness. Thus, the brightest colors in the image would change chromaticity
in addition to not getting the specified brightness boost. For
<em>decreasing</em> brightness, <b>pamfunc</b> should do the same thing as
<b>pambrighten</b>.
<p><b>ppmflash</b> does another kind of brightening. It changes the color of
each pixel to bring it a specified percentage closer to white. This increases
the value and saturation.
<p><b>pambrighten</b> is the same as <b>pambrighten</b>, except that it
recognizes the various Netpbm image formats rather than treating them all as
PPM. The output format is the same as the input format and extra channels in
a PAM image (such as a transparency channel) get passed through.
<p>If you want to modify the hues in the image, use <b>pamhue</b>.
<h2 id="examples">EXAMPLES</h2>
<p>To double the Value of each pixel:
<pre>
pambrighten -value=100
</pre>
<p>To double the Saturation and halve the Value of each pixel:
<pre>
pambrighten -saturation=+100 -value=-50
</pre>
<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>pambrighten</b> recognizes the following
command line options:
<dl>
<dt><b>-value=</b><i>value_percent</i>
<dd>This option specifies the amount, as a percentage, by which you want to
change the Value of each pixel. It may be negative.
<dt><b>-saturation=</b><i>value_percent</i>
<dd>This option specifies the amount, as a percentage, by which you want to
change the Saturation of each pixel. It may be negative.
</dl>
<h2 id="seealso">SEE ALSO</h2>
<a href="pnmnorm.html">pnmnorm</a>,
<a href="ppmdim.html">ppmdim</a>,
<a href="pamfunc.html">pamfunc</a>,
<a href="ppmflash.html">ppmflash</a>,
<a href="pamaltsat.html">pamaltsat</a>,
<a href="pamdepth.html">pamdepth</a>,
<a href="pnmgamma.html">pnmgamma</a>,
<a href="pamhue.html">pamhue</a>,
<a href="ppmhist.html">ppmhist</a>,
<a href="ppm.html">ppm</a>
<h2 id="history">HISTORY</h2>
<p><b>pambrighten</b> was new in Netphm 10.86 (March 2019). It was a
PAM conversion of the much older <b>ppmbrighten</b>.
<h2 id="author">AUTHOR</h2>
<p>Copyright (C) 1990 by Brian Moffet.
Copyright (C) 1989 by Jef Poskanzer.
<p>
Permission to use, copy, modify, and distribute this software and its
documentation for any purpose and without fee is hereby granted, provided
that the above copyright notice appear in all copies and that both that
copyright notice and this permission notice appear in supporting
documentation. This software is provided "as is" without express or
implied warranty.
<hr>
<h2 id="index">Table Of Contents</h2>
<ul>
<li><a href="#synopsis">SYNOPSIS</a>
<li><a href="#description">DESCRIPTION</a>
<li><a href="#examples">EXAMPLES</a>
<li><a href="#options">OPTIONS</a>
<li><a href="#seealso">SEE ALSO</a>
<li><a href="#history">HISTORY</a>
<li><a href="#author">AUTHOR</a>
</ul>
</body>
</html>
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