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Pgmtoppm User Manual(0)                                Pgmtoppm User Manual(0)



NAME
       pgmtoppm - colorize a PGM (grayscale) image into a PPM (color) image


SYNOPSIS
       pgmtoppm colorspec [pgmfile] pgmtoppm colorspec1-colorspec2 [pgmfile] pgmtoppm -map=mapfile [pgmfile]

       Minimum  unique  abbreviation  of option is acceptable.  You may use double hyphens instead of single hyphen to
       denote options.  You may use white space in place of the equals sign to separate an option name from its value.


DESCRIPTION
       This program is part of Netpbm(1).

       pgmtoppm  reads  a  PGM  as input and produces a PPM file as output with a specific color assigned to each gray
       value in the input.

       If you specify one color argument, black in the pgm file stays black and white in the pgm file turns  into  the
       specified  color  in  the ppm file.  Gray values in between are linearly mapped to differing intensities of the
       specified color.

       If you specify two color arguments (separated by a hyphen), then black gets mapped to the first color and white
       gets  mapped to the second and gray values in between get mapped linearly (across a three dimensional space) to
       colors in between.

       Specify the color (color) as described for the argument of the ppm_parsecolor() library routine .

       Also, you can specify an entire colormap with the -map option.  The mapfile is just a ppm file; it can  be  any
       shape,  all  that  matters is the colors in it and their order.  In this case, black gets mapped into the first
       color in the map file, and white gets mapped to the last and gray values in between are  mapped  linearly  onto
       the sequence of colors in between.  The maxval of the output image is the maxval of the map image.

       A more direct way to specify a particular color to replace each particular gray level is to use pamlookup.  You
       make an index file that explicitly associates a color with each possible gray level.


NOTE - MAXVAL
       When you don't use -map, the 'maxval,' or depth, of the output image is the same as that of  the  input  image.
       The  maxval affects the color resolution, which may cause quantization errors you don't anticipate in your out-
       put.  For example, you have a simple black and white image as a PGM with maxval 1.  Run this image through pgm-
       toppm 0f/00/00 to try to make the image black and faint red.  Because the output image will also have maxval 1,
       there is no such thing as faint red.  It has to be either full-on red or  black.   pgmtoppm  rounds  the  color
       0f/00/00 down to black, and you get an output image that is nothing but black.

       The  fix  is  easy: Pass the input through pamdepth on the way into pgmtoppm to increase its depth to something
       that would give you the resolution you need to get your desired color.  In this case, pamdepth 16 would do  it.
       Or spare yourself the unnecessary thinking and just say pamdepth 255.

       PBM  input is a special case.  While you might think this would be equivalent to a PGM with maxval 1 since only
       two gray levels are necessary to represent a PBM image, pgmtoppm, like all Netpbm programs, in fact  treats  it
       as a maxval of 255.


SEE ALSO
       pamdepth(1), rgb3toppm(1), ppmtopgm(1), ppmtorgb3(1), ppm(1), pgm(1)


AUTHOR
       Copyright (C) 1991 by Jef Poskanzer.



netpbm documentation           10 December 2006        Pgmtoppm User Manual(0)