SYNOPSIS
pbmmask [-expand] [pbmfile]


DESCRIPTION
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
background:

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
sharp.


OPTIONS
-expand




SEE ALSO
ppmcolormask, pnmpaste, pnminvert, pnmarith, pnmsmooth
pbm,


AUTHOR
Copyright (C) 1988 by Jef Poskanzer.



netpbm documentation 08 August 1989 Pbmmask User Manual(0)