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)