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Pbmmask User Manual(0)                                  Pbmmask User Manual(0)

NAME
       pbmmask - create a mask bitmap from a regular bitmap

SYNOPSIS
       pbmmask [-expand] [pbmfile]

DESCRIPTION
       This program is part of Netpbm(1).

       pbmmask  reads  a PBM image as input and Generates a corresponding mask
       of the foreground areas as another PBM image.

       The color to be interpreted as  "background"  is  determined  automati-
       cally.  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  back-
       grounds too, if you don't care about the wasted time.

       You  can  also use masks with grayscale and color images, using the pn-
       marith tool.  For instance:

           ppmtopgm obj.ppm | pamditherbw -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  pnmsmooth
       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  use-
              ful  if  you  want  a little white border around your image.  (A
              better solution might be to turn the pbmlife program into a gen-
              eral cellular automaton tool...)

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

AUTHOR
       Copyright (C) 1988 by Jef Poskanzer.

DOCUMENT SOURCE
       This manual page was generated by the Netpbm tool 'makeman'  from  HTML
       source.  The master documentation is at

              http://netpbm.sourceforge.net/doc/pbmmask.html

netpbm documentation            08 August 1989          Pbmmask User Manual(0)

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