NAME
    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 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 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 num-
    ber: #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.

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 (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 pgm-
    toppm 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 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, 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.