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.

       This is probably obsoleted by pambackground.

       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 grayscale and color images, using the pnmarith 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

       In addition to the options common to all programs based on libnetpbm (most notably -quiet,
       see
        Common Options ⟨index.html#commonoptions⟩ ), pbmmask  recognizes  the  following  command
       line option:

       -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 program into a general cellular automaton tool...)

SEE ALSO

       pambackground(1)  ppmcolormask(1),  pnmpaste(1),  pnminvert(1),  pnmarith(1), pnmsmooth(1)
       pbm(1),

AUTHOR

       Copyright (C) 1988 by Jef Poskanzer.

HISTORY

       pbmmask is one of the oldest programs in Netpbm.  In September 2021,
         the date on this manual was August 8, 1989 (being the date of the last
         substantial update).  We updated the page  then just to add this historical
         information and recommend pambackground.

       It is likely that when Bryan wrote pambackground in 2006, he was
         unaware pbmmask existed.  Otherwise, he would presumably have
         replaced pbmmask with a wrapper around pambackground.

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