pgmtoppm - colorize a portable graymap into a portable pixmap


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


   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 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.

   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   hexadecimal
          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 .


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


   Copyright (C) 1991 by Jef Poskanzer.

                            24 January 2001                    pgmtoppm(1)


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