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


SYNOPSIS

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


DESCRIPTION

       Reads a PGM as input.  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 spec­
       ified 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.

       You can specify the color in one of five ways:

       o      A name, from an X11-style color names file.

       o      An  X11-style  hexadecimal  specifier:   rgb:r/g/b,
              where  r g and b are each 1- to 4-digit hexadecimal
              numbers.

       o      An X11-style decimal specifier: rgbi:r/g/b, where r
              g and b are floating point numbers between 0 and 1.

       o      For backwards compatibility, an old-X11-style  hex­
              adecimal  number:  #rgb,  #rrggbb,  #rrrgggbbb,  or
              #rrrrggggbbbb.

       o      For backwards compatibility, a triplet  of  numbers
              separated  by  commas:  r,g,b,  where r g and b are
              floating point numbers  between  0  and  1.   (This
              style was added before MIT came up with the similar
              rgbi style.)

       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," 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 (in fact, let's say it's a PBM file,
       since pgmtoppm, like all Netpbm programs, can accept a PBM
       file as if it were PGM.  The maxval of this  image  is  1,
       because  only two gray values are needed: black and white.
       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 .


SEE ALSO

       pnmdepth(1),  rgb3toppm(1),   ppmtopgm(1),   ppmtorgb3(1),
       ppm(5), pgm(5)


AUTHOR

       Copyright (C) 1991 by Jef Poskanzer.


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