man > 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  new‐
       color.

       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 dis‐
              tance 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 be‐
              haved as if you specified this option.


       -remainder color
              ppmchange changes all pixels which are not of a color for which  you  specify  an  ex‐
              plicit 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 AT usc.edu) with modifications by Alberto Accomazzi (alberto AT cfa.har‐
       vard.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)