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Ppmchange User Manual(0)						 Ppmchange User Manual(0)

NAME
       ppmchange - change all pixels of one color to another in a PPM image

SYNOPSIS
       ppmchange

       [-closeness=closeness_percent] [-remainder=remainder_color] [-closeok] [oldcolor newcolor]
       ...  [ppmfile]

EXAMPLES
       ppmchange red blue redimage.ppm >blueimage.ppm

       ppmchange red red -remainder=black myimage.ppm >redblack.ppm

       ppmchange -closeness=90 white white black black

DESCRIPTION
       This program is part of Netpbm(1)

       ppmchange reads a PPM image as input and changes all pixels of  color  oldcolor	to  color
       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.

       Specify the colors as described for the argument of the ppm_parsecolor()  library  routine
       <libppm.html#colorname> .

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

       The maxval of the output image is the same as that of the input image.  If a newcolor  you
       specify cannot be exactly represented in that maxval, ppmchange assumes a color that is as
       close as possible to what you specified but can be represented with your  maxval.   Unless
       you specify the -closeok option, ppmchange issues a warning that it is using an approxima-
       tion.

       A common way that you can have this maxval problem, where the color you specify cannot  be
       represented with your maxval, is that your input is a PBM (black and white) image that you
       are colorizing.	The maxval in this case is 1, which severely limits the colors	to  which
       you  can  change.   To  avoid  this problem, use pamdepth to make the maxval of your input
       something consistent with your colors.  255 is usually a good choice.

       Before Netpbm 10.22 (April 2004), ppmchange  always  behaved  as  if  the  user	specified
       -closeok and there was no -closeok option.

OPTIONS
       -closeness closeness_percent
	      closeness  is an integer percentage 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 per cent of the maxval.

	      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.

	      This option was new in Netpbm 9.8 (September 2000).

       -closeok
	      This  option affects how ppmchange interprets a color you specify in the arguments.
	      When you specify this option, ppmchange may use a color close to, but not the  same
	      as what you specify.  See the description section <#description>	for details.

	      This  option  was  new in Netpbm 10.22 (April 2004).  Before that, ppmchange always
	      behaved as if you specified this option.

       -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(1)

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

netpbm documentation			  September 2005		 Ppmchange User Manual(0)
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