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.