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NAME

       pnmremap - replace colors in a PPM image with colors from another set

SYNOPSIS

       pnmremap    [-floyd|-fs|-nfloyd|-nofs]   [-firstisdefault]   [-verbose]
       [-mapfile=mapfile] [-missingcolor=color] [pnmfile]

       All options can be abbreviated to their shortest  unique  prefix.   You
       may use two hyphens instead of one to designate an option.  You may use
       either white space or an equals sign between an  option  name  and  its
       value.

DESCRIPTION

       pnmremap  replaces  the  colors  in  an  input  image with those from a
       colormap you specify.  Where a  color  in  the  input  is  not  in  the
       colormap,  you have three choices: 1) choose the closest color from the
       colormap; 2) choose the first color from the colormap; 3) use  a  color
       specified  by a command option.  (In this latter case, if the color you
       specify is not in your color  map,  the  output  will  not  necessarily
       contain only colors from the colormap).

       Two  reasons to do this are: 1) you want to reduce the number of colors
       in the input image; and 2) you need to feed the image to something that
       can handle only certain colors.

       To  reduce  colors,  you  can  generate  the colormap with ppmcolormap.
       Example:

       ppmcolormap testimg.ppm 256 >colormap.ppm
       ppmremap -map=colormap.ppm testimg.ppm
       >reduced_testimg.ppm

       To limit colors to a certain set, a typical example  is  to  create  an
       image  for posting on the World Wide Web, where different browsers know
       different colors.  But all browsers are supposed to know the  216  "web
       safe"  colors which are essentially all the colors you can represent in
       a PPM image with a maxval of 5.  So you can do this:

       ppmcolors 5 >websafe.ppm
       ppmremap -map=webafe.ppm testimg.ppm >websafe_testimg.ppm

       The output image has the same type and maxval as the map file.

PARAMETERS

       There is one parameter, which is required:  The  file  specifcation  of
       the input PNM file.

       OPTIONS

       -floyd -fs  -nofloyd  -nofs  These  options  determine  whether  Floyd-
              Steinberg  dithering  is  done.   Without  Floyd-Steinberg,  the
              selection  of  output  color of a pixel is based on the color of
              only  the  corresponding  input  pixel.   With  Floyd-Steinberg,
              multiple  input  pixels are considered so that the average color
              of an area tends to stay  more  the  same  than  without  Floyd-
              Steinberg.  For example, if you map an image with a black, gray,
              gray, and white pixel adjacent, through a map that contains only
              black  and  white, it might result in an output of black, black,
              white, white.  Pixel-by-pixel mapping would instead map both the
              gray pixels to the same color.

              -fs is a synomym for -floyd.  -nofs is a synonym for -nofloyd.

              The default is -nofloyd.

       -firstisdefault
              This  affects what happens with a pixel in the input image whose
              color  is  not  in  the  map  file.   If  you  specify   neither
              -firstisdefault  nor  -missingcolor,  pnmremap  chooses  for the
              output the color in the map which is closest to the color in the
              input.   With  -firstisdefault,  pnmremap instead uses the first
              color in the colormap.

              If you specify -firstisdefault, the maxval of  your  input  must
              match the maxval of your colormap.

       -missingcolor=color
              This  affects what happens with a pixel in the input image whose
              color  is  not  in  the  map  file.   If  you  specify   neither
              -firstisdefault  nor  -missingcolor,  pnmremap  chooses  for the
              output the color in the map which is closest to the color in the
              input.  With -missingcolor, pnmremap uses color.  color need not
              be in the colormap.

              If you specify -missingcolor, the  maxval  of  your  input  must
              match the maxval of your colormap.

       -verbose
              Display helpful messages about the mapping process.

SEE ALSO

       pnmcolormap(1), ppmcolors(1), pnmquant(1), ppmquantall(1), pnmdepth(1),
       ppmdither(1), ppmquant(1), ppm(5)

AUTHOR

       Copyright (C) 1989, 1991 by Jef Poskanzer.  Copyright (C) 2001 by Bryan
       Henderson.

                                01 January 2002                    pnmremap(1)