man > pgmtoppm(1)

Pgmtoppm User Manual(1)                General Commands Manual               Pgmtoppm User Manual(1)

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


SYNOPSIS
       pgmtoppm [-black=colorspec1] [-white=colorspec2]
        [pgmfile]  pgmtoppm  -map=filename  [pgmfile]  pgmtoppm  colorspec [pgmfile] pgmtoppm color‐
       spec1-colorspec2 [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 sep‐
       arate an option name from its value.


DESCRIPTION
       This program is part of Netpbm(1).

       If all you want to do is convert PGM to PPM, keeping the same gray pixels,
         you may not need to.  All Netpbm programs that expect PPM input also
         recognize PGM.  And if you must have a PPM file, use ppmtoppm
         instead.  It is more efficient and easier to use.

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

       You can specify the color in the output to which black in the input maps,
         and the color to which white maps.  All the gray values in between map
         linearly (across a three dimensional space) to colors between the black and
         white colors you specify.

       Use the -black and -white options for this.  For historical
         reasons, you can alternatively use a non-option argument to specify the
         colors.  If you do that, pgmtoppm interprets the color argument
         like this: if the argument takes the form black-white,
         it has the effect of -black=black -white=white
         If instead there is no hyphen in the color argument, it has the effect of
         -white=color_argument.

       Because of the historical syntax, it is not possible to let both
         -black and -white default (but you shouldn't want to --
         see below for advice on making such a null conversion).


       You can alternatively specify an entire colormap with the -map option.


       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.



OPTIONS
       In addition to the options common to all programs based on libnetpbm  (most  notably  -quiet,
       see ]8;;index.html#commonoptions\ Common Options]8;;\ ), pgmtoppm recognizes the following command line options:




       -black=colorspec
              The  program  maps black pixels in the input to this color in the output.  The default
              is black.

              Specify the color (color) as described  for  the  ]8;;libnetpbm_image.html#colorname\argument of the pnm_parsecolor() li‐
              brary routine]8;;\ .

              You cannot specify this together with -map.

              This option was new in Netpbm 10.97 (December 2021).  Before that,
                use the color argument.


       -white=colorspec
              The  program  maps white pixels in the input to this color in the output.  The default
              is white.

              Specify the color (color) as described  for  the  ]8;;libnetpbm_image.html#colorname\argument of the pnm_parsecolor() li‐
              brary routine]8;;\ .

              You cannot specify this together with -map.

              This option was new in Netpbm 10.97 (December 2021).  Before that,
                use the color argument.


       -map=filename
              This option specifies a complete mapping of gray values in the input to
                  color values in the output.  The map file (named filename) 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.





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  er‐
       rors you don't anticipate in your output.  For example, you have a simple black and white im‐
       age  as a PGM with maxval 1.  Run this image through pgmtoppm 0f/00/00 to try to make the im‐
       age 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
       ppmtoppm(1), pamdepth(1), rgb3toppm(1), ppmtopgm(1), ppmtorgb3(1), ppm(1), pgm(1)


AUTHOR
       Copyright (C) 1991 by Jef Poskanzer.

DOCUMENT SOURCE
       This manual page was generated by the Netpbm tool 'makeman' from  HTML  source.   The  master
       documentation is at

              http://netpbm.sourceforge.net/doc/pgmtoppm.html

netpbm documentation                       02 October 2021                   Pgmtoppm User Manual(1)