This is the command ppmchange that can be run in the OnWorks free hosting provider using one of our multiple free online workstations such as Ubuntu Online, Fedora Online, Windows online emulator or MAC OS online emulator
PROGRAM:
NAME
ppmchange - change all pixels of one color to another in a portable pixmap
SYNOPSIS
ppmchange [ -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 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.
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 hexadecimal 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, ppmchange replaces it with the newcolor
of the leftmost 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, 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.
-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.
Use ppmchange online using onworks.net services
