ppmchange(1)ppmchange(1)NAMEppmchange - change all pixels of one color to another in a
portable pixmap
SYNOPSISppmchange [ -closeness closeness_percent ] [ -remainder
remainder_color ] [ oldcolor newcolor ] ... [ppmfile]
DESCRIPTION
Reads a portable pixmap as input. Changes all pixels of
oldcolor to newcolor. You may specify up to 256 old
color/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 "close
ness" factor.
The colors can be specified in five ways:
o A name, assuming that a pointer to an X11-style
color names file was compiled in.
o An X11-style hexadecimal specifier: rgb:r/g/b,
where r g and b are each 1- to 4-digit hexadecimal
numbers.
o An X11-style decimal specifier: rgbi:r/g/b, where r
g and b are floating point numbers between 0 and 1.
o For backwards compatibility, an old-X11-style hex
adecimal number: #rgb, #rrggbb, #rrrgggbbb, or
#rrrrggggbbbb.
o For backwards compatibility, a triplet of numbers
separated by commas: r,g,b, where r g and b are
floating point numbers between 0 and 1. (This
style was added before MIT came up with the similar
rgbi style.)
If a pixel matches two different oldcolors, ppm
change replaces it with the newcolor of the left
most specified one.
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.
The "distance" in color is defined as the cartesian
sum of the individual differences in red, green,
and blue intensities between the two pixels, nor
malized 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 vari
ously 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.
-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 ALSOpgmtoppm(1), ppmcolormask(1), ppm(5)AUTHOR
Wilson H. Bent. Jr. (whb@usc.edu) with modifications by
Alberto Accomazzi (alberto@cfa.harvard.edu)
07 January 2001 ppmchange(1)
