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 ), 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

netpbm documentation                            28 September 2021                         Pbmmask User Manual(1)