Pbmmask User Manual(0) Pbmmask User Manual(0)NAMEpbmmask - create a mask bitmap from a regular bitmap
SYNOPSISpbmmask [-expand] [pbmfile]
DESCRIPTION
This program is part of Netpbm(1).
pbmmask reads a PBM image as input and Generates a corresponding mask
of the foreground areas as another PBM image.
The color to be interpreted as 'background' is determined automati‐
cally. 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 back‐
grounds too, if you don't care about the wasted time.
You can also use masks with grayscale and color images, using the
pnmarith tool. For instance:
ppmtopgm obj.ppm | pamditherbw -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 pnmsmooth
before using it. This makes the boundary between the two images less
sharp.
OPTIONS-expand
Expands the mask by one pixel out from the image. This is use‐
ful if you want a little white border around your image. (A
better solution might be to turn the pbmlife program into a gen‐
eral cellular automaton tool...)
SEE ALSOppmcolormask(1), pnmpaste(1), pnminvert(1), pnmarith(1), pnmsmooth(1)pbm(1),
AUTHOR
Copyright (C) 1988 by Jef Poskanzer.
netpbm documentation 08 August 1989 Pbmmask User Manual(0)
