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)