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


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


   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.


   -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

   -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.


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


   Wilson  H.  Bent.  Jr.  (whb@usc.edu)  with  modifications  by  Alberto
   Accomazzi (alberto@cfa.harvard.edu)

                            07 January 2001                   ppmchange(1)


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