NAME
    ppmchange - change all pixels of one color to another in a portable
    pixmap

SYNOPSIS
    ppmchange [ -closeness closeness_percent ] [ -remainder remainder_color
    ] [ oldcolor newcolor ] ... [ppmfile]

DESCRIPTION
    Reads a  portable pixmap as input. Changes all pixels of oldcolor to
    newcolor. You may specify up to 256 oldcolor/newcolor pairs on the
    command line. ppmchange leaves all colors not mentioned unchanged,
    unless you specify the -remainder option, in which case they are all
    changed to the single specified color.

    You can specify that colors similar, but not identical, to the ones you
    specify get replaced by specifying a "closeness" factor.

    The colors can be specified in five ways:

    o   A name, assuming that a pointer to an X11-style color names file
    was compiled in.

    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.)

    If a pixel matches two different oldcolors, ppmchange replaces
    it with the newcolor of the leftmost specified one.

OPTIONS
    -closeness closeness_percent
    closeness is an integer per centage indicating how close to the
    color you specified a pixel must be  to get replaced. By
    default, it is 0, which means the pixel must be the exact  color
    you specified.

    A  pixel gets replaced if the distance in color between it and
    the color you specified is less than or equal to closeness.

    The "distance" in color is defined as the cartesian sum of the
    individual differences in red,  green,  and blue intensities
    between the two pixels,  normalized so  that the difference
    between black and white is 100%.

    This is probably simpler than what you want most the time. You
    probably would like to change colors that have similar chromi-
    nance, regardless of their intensity. So if there's a red barn
    that is variously shadowed, you want the entire barn changed.
    But because the  shadowing significantly changes the  color
    according to ppmchange's distance formula, parts of the barn are
    probably about as distant in color from other parts of the barn
    as they are from green grass next to the barn.

    Maybe ppmchange will be enhanced some day to do chrominance
    analysis.

    -remainder color
    ppmchange  changes all pixels which are not of a color for which
    you specify an explicit replacement color on the command line to
    color color.

    An example application of this is

    ppmchange -remainder=black red red

    to lift only the red portions from an image, or

    ppmchange -remainder=black red white | ppmtopgm

    to create a mask file for the red portions of the image.

SEE ALSO
   pgmtoppm(1),ppmcolormask(1), ppm(5)

AUTHOR
    Wilson H. Bent. Jr. (whb@usc.edu) with modifications by Alberto Acco-
    mazzi (alberto@cfa.harvard.edu)