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pbmmask(1)									       pbmmask(1)

       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 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 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 useful 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(1), pnmpaste(1), pnminvert(1), pbm(5), pnmarith(1), pnmsmooth(1)

       Copyright (C) 1988 by Jef Poskanzer.

					  08 August 1989			       pbmmask(1)
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