pbmmask [-expand] [pbmfile]

This program is part of Netpbm.

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

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 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


ppmcolormask, pnmpaste, pnminvert, pnmarith, pnmsmooth

Copyright (C) 1988 by Jef Poskanzer.

netpbm documentation 08 August 1989 Pbmmask User Manual(0)