114 lines
2.8 KiB
HTML
114 lines
2.8 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML><HEAD><TITLE>Man page of pnmconvol</TITLE>
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</HEAD><BODY>
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<H1>pnmconvol</H1>
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Section: User Commands (1)<BR>Updated: 26 November 1994<BR><A HREF="#index">Index</A>
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<A HREF="/cgi-bin/man/man2html">Return to Main Contents</A><HR>
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<A NAME="ixAAB"></A>
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<A NAME="lbAB"> </A>
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<H2>NAME</H2>
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pnmconvol - general MxN convolution on a portable anymap
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<A NAME="lbAC"> </A>
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<H2>SYNOPSIS</H2>
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<B>pnmconvol</B>
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<I>convolutionfile</I>
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[<I>pnmfile</I>]
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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Reads two portable anymaps as input.
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Convolves the second using the first,
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and writes a portable anymap as output.
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<A NAME="ixAAC"></A>
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<P>
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Convolution means replacing each pixel with a weighted average of the
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nearby pixels. The weights and the area to average are determined by
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the convolution matrix.
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The unsigned numbers in the convolution file are offset by -maxval/2 to
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make signed numbers, and then normalized, so the actual values in the
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convolution file are only relative.
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<P>
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Here is a sample convolution file;
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it does a simple average of the nine immediate neighbors, resulting
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in a smoothed image:
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<PRE>
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P2
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3 3
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18
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10 10 10
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10 10 10
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10 10 10
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</PRE>
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<P>
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To see how this works, do the above-mentioned offset: 10 - 18/2 gives 1.
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The possible range of values is from 0 to 18, and after the offset
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that's -9 to 9. The normalization step makes the range -1 to 1, and
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the values get scaled correspondingly so they become 1/9 - exactly what
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you want.
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The equivalent matrix for 5x5 smoothing would have maxval 50 and be
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filled with 26.
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<P>
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The convolution file will usually be a graymap,
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so that the same convolution gets applied to each color component.
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However, if you want to use a pixmap and do a different convolution to
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different colors, you can certainly do that.
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<P>
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At the edges of the convolved image, where the convolution matrix would
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extend over the edge of the image,
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<B>pnmconvol</B>
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just copies the input pixels directly to the output.
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<P>
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<A NAME="lbAE"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?1+pnmsmooth">pnmsmooth</A></B>(1),
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<B><A HREF="/cgi-bin/man/man2html?5+pnm">pnm</A></B>(5)
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<P>
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<A NAME="lbAF"> </A>
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<H2>AUTHORS</H2>
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Copyright (C) 1989, 1991 by Jef Poskanzer.
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<BR>
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Modified 26 November 1994 by Mike Burns, <A HREF="mailto:burns@chem.psu.edu">burns@chem.psu.edu</A>
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<P>
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<HR>
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<A NAME="index"> </A><H2>Index</H2>
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<DL>
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<DT id="1"><A HREF="#lbAB">NAME</A><DD>
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<DT id="2"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="3"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="4"><A HREF="#lbAE">SEE ALSO</A><DD>
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<DT id="5"><A HREF="#lbAF">AUTHORS</A><DD>
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</DL>
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<HR>
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This document was created by
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<A HREF="/cgi-bin/man/man2html">man2html</A>,
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using the manual pages.<BR>
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Time: 00:05:24 GMT, March 31, 2021
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