pbmmask Man page

pbmmask General Commands Manual pbmmask


pbmmask – create a mask bitmap from a regular bitmap


pbmmask [-expand] [pbmfile]


Reads a portable bitmap as input. Creates a corresponding mask bitmap
and writes it out.

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
pbmmask obj > objmask
pnmpaste < dest -and objmask | pnmpaste -or obj
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 | pnmpaste -or blackback
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 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.


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 tool into a general
cellular automaton tool…)


ppmcolormask, pnmpaste, pnminvert, pbm(5), pnmarith,


Copyright (C) 1988 by Jef Poskanzer.

08 August 1989 pbmmask