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
       ⟨libnetpbm_image.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
       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 ⟨index.html#commonoptions⟩ ), 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 ⟨#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)

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