pnmremap

pnmremap(1)                 General Commands Manual                pnmremap(1)

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

SYNOPSIS
       pnmremap [-floyd|-fs|-nfloyd|-nofs] [-firstisdefault] [-verbose] [-map-
       file=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 col-
       ormap 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.  Ex-
       ample:

       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 im-
       age  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-Stein-
              berg 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  exam-
              ple,  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  -firstis-
              default  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  -firstis-
              default  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)