Manual: ppmchange

Ppmchange User Manual(1)			   General Commands Manual			    Ppmchange User Manual(1)

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=10 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 un‐
       changed, 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 "close‐
       ness" factor.

       Specify the colors as described for the argument of the pnm_parsecolor() library routine .

       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
       approximation.

       A common way that you can have this maxval problem, where the color you specify cannot be represented with your	max‐
       val,  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
       In addition to the options common to all programs based on libnetpbm (most notably  -quiet,  see	  Common Options  ),
       ppmchange recognizes the following command line options:

       -closeness closeness_percent
	      closeness is a 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 specified 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 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 ppm‐
	      change'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 op‐
	      tion, ppmchange may use a color close to, but not the same as what you specify.  See the description section
	      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)

DOCUMENT SOURCE
       This manual page was generated by the Netpbm tool 'makeman' from HTML source.  The master documentation is at

	      http://netpbm.sourceforge.net/doc/ppmchange.html

netpbm documentation					December 2016				    Ppmchange User Manual(1)