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  dou-
       ble  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 intensi-
       ties 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 <libppm.html#colorname> .

       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 partic-
       ular 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 res-
       olution,	 which	may  cause quantization errors you don't anticipate in
       your output.  For example, you have a simple black and white image as a
       PGM  with maxval 1.  Run this image through pgmtoppm 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 pgm-
       toppm to increase its depth to something that would give you the	 reso-
       lution  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 neces-
       sary  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)