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)