132 lines
2.9 KiB
HTML
132 lines
2.9 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 pbmreduce</TITLE>
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</HEAD><BODY>
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<H1>pbmreduce</H1>
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Section: User Commands (1)<BR>Updated: 02 August 1989<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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pbmreduce - read a portable bitmap and reduce it N times
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<A NAME="lbAC"> </A>
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<H2>SYNOPSIS</H2>
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<B>pbmreduce</B>
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[<B>-floyd</B>|<B>-fs</B>|<B>-threshold</B>
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]
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[<B>-value</B>
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<I>val</I>]
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<I>N</I>
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[<I>pbmfile</I>]
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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Reads a portable bitmap as input.
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Reduces it by a factor of
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<I>N</I>,
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and produces a portable bitmap as output.
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<A NAME="ixAAC"></A>
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<P>
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<I>pbmreduce</I>
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duplicates a lot of the functionality of
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<I>pgmtopbm;</I>
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<A NAME="ixAAD"></A>
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you could do something like
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<B>pnmscale | pgmtopbm,</B>
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<A NAME="ixAAE"></A>
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but
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<I>pbmreduce</I>
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is a lot faster.
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<P>
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<I>pbmreduce</I>
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can be used to "re-halftone" an image.
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<A NAME="ixAAF"></A>
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Let's say you have a scanner that only produces black&white, not
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grayscale, and it does a terrible job of halftoning (most b&w scanners
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fit this description).
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One way to fix the halftoning is to scan at the highest possible
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resolution, say 300 dpi, and then reduce by a factor of three or
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so using
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<I>pbmreduce</I>.
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You can even correct the brightness of an image, by using the
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<B>-value</B>
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flag.
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<A NAME="lbAE"> </A>
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<H2>OPTIONS</H2>
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<P>
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By default, the halftoning after the reduction is done via
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boustrophedonic Floyd-Steinberg error diffusion; however, the
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<A NAME="ixAAG"></A>
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<A NAME="ixAAH"></A>
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<B>-threshold</B>
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flag can be used to specify simple thresholding. This gives better
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<A NAME="ixAAI"></A>
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results when reducing line drawings.
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<P>
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The
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<B>-value</B>
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flag alters the thresholding value for all quantizations.
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It should be a real number between 0 and 1.
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Above 0.5 means darker images; below 0.5 means lighter.
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<P>
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All flags can be abbreviated to their shortest unique prefix.
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<A NAME="lbAF"> </A>
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<H2>SEE ALSO</H2>
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<A HREF="/cgi-bin/man/man2html?1+pnmenlarge">pnmenlarge</A>(1), <A HREF="/cgi-bin/man/man2html?1+pnmscale">pnmscale</A>(1), <A HREF="/cgi-bin/man/man2html?1+pgmtopbm">pgmtopbm</A>(1), <A HREF="/cgi-bin/man/man2html?5+pbm">pbm</A>(5)
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<A NAME="lbAG"> </A>
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<H2>AUTHOR</H2>
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Copyright (C) 1988 by Jef Poskanzer.
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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">OPTIONS</A><DD>
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<DT id="5"><A HREF="#lbAF">SEE ALSO</A><DD>
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<DT id="6"><A HREF="#lbAG">AUTHOR</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: 00:05:21 GMT, March 31, 2021
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</BODY>
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</HTML>
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