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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)



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