172 lines
3.8 KiB
HTML
172 lines
3.8 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 ppmquant</TITLE>
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</HEAD><BODY>
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<H1>ppmquant</H1>
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Section: User Commands (1)<BR>Updated: 12 January 1991<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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ppmquant - quantize the colors in a portable pixmap down to a specified number
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<A NAME="lbAC"> </A>
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<H2>SYNOPSIS</H2>
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<B>ppmquant</B>
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[<B>-floyd</B>|<B>-fs</B>]
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<I>ncolors</I>
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[<I>ppmfile</I>]
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<BR>
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<B>ppmquant</B>
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[<B>-floyd</B>|<B>-fs</B>]
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[<B>-nofloyd</B>|<B>-nofs</B>]
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<B>-mapfile</B>
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<I>mapfile</I>
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[<I>ppmfile</I>]
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<P>
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All options can be abbreviated to their shortest unique prefix. You
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may use two hyphens instead of one to designate an option. You may
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use either white space or equals signs between an option name and its
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value.
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<P>
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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<B>pnmquant </B>
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is a newer, more general program that is backward compatible with
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<B>ppmquant</B>.
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<B>ppmquant</B>
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may be faster, though.
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<P>
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Reads a PPM image as input. Chooses
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<I>ncolors</I>
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colors to best represent the image, maps the existing colors
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to the new ones, and writes a PPM image as output.
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<A NAME="ixAAC"></A>
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<P>
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The quantization method is Heckbert's "median cut".
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<A NAME="ixAAD"></A>
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<P>
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Alternately, you can skip the color-choosing step by
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specifying your own set of colors with the
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<B>-mapfile</B>
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option. The
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<I>mapfile</I>
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is just a
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<I>ppm</I>
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file; it can be any shape, all that matters is the colors in it.
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For instance, to quantize down to the 8-color IBM TTL color set, you
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might use:
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<PRE>
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P3
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8 1
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255
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0 0 0
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255 0 0
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0 255 0
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0 0 255
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255 255 0
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255 0 255
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0 255 255
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255 255 255
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</PRE>
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If you want to quantize one image to use the colors in another one,
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just use the second one as the mapfile. You don't have to reduce it
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down to only one pixel of each color, just use it as is.
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<P>
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If you use a mapfile, the output image has the same maxval as the
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mapfile. Otherwise, the output maxval is the same as the input
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maxval, or less in some cases where the quantization process reduces
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the necessary resolution.
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<P>
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<P>
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The
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<B>-floyd</B>/<B>-fs</B>
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option enables a Floyd-Steinberg error diffusion step.
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<A NAME="ixAAE"></A>
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<A NAME="ixAAF"></A>
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Floyd-Steinberg gives vastly better results on images where the unmodified
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quantization has banding or other artifacts, especially when going to a
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small number of colors such as the above IBM set.
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However, it does take substantially more CPU time, so the default is off.
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<P>
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<B>-nofloyd</B>/<B>-nofs</B>
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means not to use the Floyd-Steinberg error diffusion. This is the default.
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<P>
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<A NAME="lbAE"> </A>
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<H2>REFERENCES</H2>
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"Color Image Quantization for Frame Buffer Display" by Paul Heckbert,
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SIGGRAPH '82 Proceedings, page 297.
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<P>
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<A NAME="lbAF"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?1+pnmquant">pnmquant</A></B>(1),
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<B><A HREF="/cgi-bin/man/man2html?1+ppmquantall">ppmquantall</A></B>(1),
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<B><A HREF="/cgi-bin/man/man2html?1+pnmdepth">pnmdepth</A></B>(1),
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<B><A HREF="/cgi-bin/man/man2html?1+ppmdither">ppmdither</A></B>(1),
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<B><A HREF="/cgi-bin/man/man2html?5+ppm">ppm</A></B>(5)
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<P>
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<A NAME="lbAG"> </A>
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<H2>AUTHOR</H2>
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Copyright (C) 1989, 1991 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">REFERENCES</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: 00:05:25 GMT, March 31, 2021
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