ppmchange

ppmchange(1)                General Commands Manual               ppmchange(1)

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, un-
       less 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 be-
              tween 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 de-
              fault, 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 be-
              tween 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 ac-
              cording 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)

                                07 January 2001                   ppmchange(1)