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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 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  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 boundary 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)
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