ppmchange



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  colr
       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_parsec-
       olor() 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 pnmdepth 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 per centage 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  chromi-
              nance,  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.


       -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 Acco-
       mazzi (alberto@cfa.harvard.edu)



netpbm documentation            September 2005        Ppmchange User Manual(0)

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