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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 3.2//EN">
<HTML><HEAD><TITLE>Ppmmix User Manual</TITLE></HEAD>
<BODY>
<H1>ppmmix</H1>
Updated: 23 March 2010
<BR>
<A HREF="#index">Table Of Contents</A>
<H2>NAME</H2>
ppmmix - blend together two PPM images
<H2 id="synopsis">SYNOPSIS</H2>
ppmmix <I>fadefactor</I> <I>ppmfile1</i> <i>ppmfile2</I>
<H2 id="description">DESCRIPTION</H2>
<p>This program is part of <a href="index.html">Netpbm</a>.
<p><b>ppmmix</b> reads two PPM images as input and mixes them together
using the specified fade factor. The fade factor may be in the range
from 0.0 (only ppmfile1's image data) to 1.0 (only ppmfile2's image
data). Anything in between specifies a smooth blend between the two
images.
<P>The two images must have the same dimensions, the same maxval, and the
same type (PBM/PGM/PPM).
<p>The fade factor is applied to brightness, not light intensity. That means
for example that if you have a series of images you generated
using <b>ppmmix</b> of a black and a white image with a linearly increasing
fade factor, you will see an image getting linearly brighter, but the light
intensity will increase faster at the end. That is because it requires more
intensity change at the bright end of the scale than at the dark end for the
human eye to perceive the same brightness change. This also means that
if the original images aren't all one color, the mixed image is distorted,
since the intensity relationship between pixels is different from the
original image.
<P><B>pamcomp</B> is a more general alternative. It allows you to mix
images of different size and to have the fade factor vary throughout
the image (through the use of an alpha mask). It does not have the
same-maxval and same-type restrictions. It mixes light intensity, not
brightness.
<H2 id="seealso">SEE ALSO</H2>
<B><A HREF="pamcomp.html">pamcomp</A></B>,
<B><A HREF="ppm.html">ppm</A></B>
<H2 id="author">AUTHOR</H2>
Copyright (C) 1993 by Frank Neumann
<HR>
<A NAME="index"> </A>
<H2>Table Of Contents</H2>
<UL>
<LI><A HREF="#synopsis">SYNOPSIS</A>
<LI><A HREF="#description">DESCRIPTION</A>
<LI><A HREF="#seealso">SEE ALSO</A>
<LI><A HREF="#author">AUTHOR</A>
</UL>
</BODY>
</HTML>
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