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Pbmmask User Manual(0)                                  Pbmmask User Manual(0)



NAME
       pbmmask - create a mask bitmap from a regular bitmap


SYNOPSIS
       pbmmask [-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 automatically.  Regardless of which  color  is  back-
       ground, 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 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  bound-
       ary between the two images less sharp.


OPTIONS
       -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  program  into  a  general  cellular
              automaton tool...)




SEE ALSO
       ppmcolormask(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)