ppmchange(1) - man - phpman

Che Dong

⚡ TLDR: ppmchange (tldr-pages)

Change all pixels of one color in a PPM image to another color.

Exchange the first color in each `oldcolor` - `newcolor` pair with the second color
ppmchange {{oldcolor1 newcolor1 oldcolor2 newcolor2 ...}} {{path/to/input.ppm}} > {{path/to/output.ppm}}
Specify how similar colors must be in order to be considered the same
ppmchange -closeness {{percentage}} {{oldcolor1 newcolor1 oldcolor2 newcolor2 ...}} {{path/to/input.ppm}} > {{path/to/output.ppm}}
Replace all pixels not specified in the arguments by a color
ppmchange {{-r|-remainder}} {{color}} {{oldcolor1 newcolor1 oldcolor2 newcolor2 ...}} {{path/to/input.ppm}} > {{path/to/output.ppm}}

ppmchange(1) General Commands Manual ppmchange(1)

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 spec‐
ify 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 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.

-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(5)

AUTHOR
Wilson H. Bent. Jr. (whb AT usc.edu) with modifications by Alberto Accomazzi (alberto AT cfa.har‐
vard.edu)

07 January 2001 ppmchange(1)