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



Table Of Contents


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


SYNOPSIS
       pgmtoppm

       colorspec

       [pgmfile] pgmtoppm

       colorspec1-colorspec2

       [pgmfile] pgmtoppm -map

       mapfile

       [pgmfile]


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
       dash),  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.

       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
       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 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 pnmdepth 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, pnmdepth 16 would do it.
       Or spare yourself the unnecessary thinking and just  say
       pnmdepth 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
       pnmdepth(1),  rgb3toppm(1),  ppmtopgm(1),  ppmtorgb3(1),
       ppm(1), pgm(1)


AUTHOR
       Copyright (C) 1991 by Jef Poskanzer.



netpbm documentation    24 January 2001 Pgmtoppm User Manual(0)
