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RedHat 9 (Linux i386) - man page for ppmchange (redhat section 1)

ppmchange(1)			     General Commands Manual			     ppmchange(1)

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

       ppmchange  [ -closeness closeness_percent ] [ -remainder remainder_color ] [ oldcolor new-
       color ] ...  [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 col-
       ors 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 num-
	      bers 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  speci-
	      fied is less than or equal to closeness.

	      The  "distance"  in color is defined as the cartesian sum of the individual differ-
	      ences 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.

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

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

					 07 January 2001			     ppmchange(1)

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