pbmmask(1)               UNIX System V(08 August 1989)               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.

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

AUTHOR
      Copyright (C) 1988 by Jef Poskanzer.







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