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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
              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.)

              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
              chrominance, 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
       Accomazzi (alberto@cfa.harvard.edu)

                                07 January 2001                   ppmchange(1)