xfree86 man page for pbmmask

pbmmask(1)						      General Commands Manual							pbmmask(1)

NAME
       pbmmask - create a mask bitmap from a regular bitmap

SYNOPSIS
       pbmmask [-expand] [pbmfile]

DESCRIPTION
       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.

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 tool into a general cellular automaton tool...)

SEE ALSO
       ppmcolormask(1), pnmpaste(1), pnminvert(1), pbm(5), pnmarith(1), pnmsmooth(1)

AUTHOR
       Copyright (C) 1988 by Jef Poskanzer.

								  08 August 1989							pbmmask(1)