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 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 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 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

       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 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  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)