man > pbmmask(1)

Pbmmask User Manual(1)                 General Commands Manual                Pbmmask User Manual(1)

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 fig‐
       ure 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 in‐
       stance:

           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 ]8;;index.html#commonoptions\ Common Options]8;;\ ), 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 pro‐
              gram 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)