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)