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pbmmask.man
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1995-03-17
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pbmmask(1) AMIGA (08 August 1989) pbmmask(1)
NAME
pbmmask - create a mask bitmap from a regular bitmap
SYNOPSIS
pbmmask [-expand] [pbmfile]
DESCRIPTION
Reads a portable bitmap as input. Creates a corresponding
mask bitmap and writes it out.
The color to be interpreted as "background" is determined
automatically. Regardless of which color is background, the
mask will be white where the background is and black where
the figure is.
This lets you do a masked paste like this, for objects with
a black background:
pbmmask obj > objmask
pnmpaste < dest -and objmask <x> <y> | pnmpaste -or obj <x> <y>
For objects with a white background, you can either invert
them or add a step:
pbmmask obj > objmask
pnminvert objmask | pnmpaste -and obj 0 0 > blackback
pnmpaste < dest -and objmask <x> <y> | pnmpaste -or blackback <x> <y>
Note that this three-step version works for objects with
black backgrounds too, if you don't care about the wasted
time.
You can also use masks with graymaps and pixmaps, using the
pnmarith tool. For instance:
ppmtopgm obj.ppm | pgmtopbm -threshold | pbmmask > objmask.pbm
pnmarith -multiply dest.ppm objmask.pbm > t1.ppm
pnminvert objmask.pbm | pnmarith -multiply obj.ppm - > t2.ppm
pnmarith -add t1.ppm t2.ppm
An interesting variation on this is to pipe the mask through
the pnmsmooth script before using it. This makes the
boundary between the two images less sharp.
-expand
Expands the mask by one pixel out from the image. This
is useful if you want a little white border around your
image. (A better solution might be to turn the pbmlife
tool into a general cellular automaton tool...)
SEE ALSO
pnmpaste(1), pnminvert(1), pbm(5), pnmarith(1), pnmsmooth(1)
AUTHOR
Copyright (C) 1988 by Jef Poskanzer.
Page 1 (printed 10/19/91)