Manual: pbmmask

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 figure is.

       This lets you do a masked paste like this, for objects with a black background:

	   pbmmask obj > objmask
	   pnmpaste < dest -and objmask   | pnmpaste -or obj  

       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   | pnmpaste -or blackback  

       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 be‐
       tween the two images less sharp.

OPTIONS
       In addition to the options common to all programs based on libnetpbm (most notably -quiet, see  Common Options ), pb‐
       mmask 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)