NAME

pbmmask - create a mask bitmap from a regular bitmap

SYNOPSIS

pbmmask [pbmfile]

DESCRIPTION

Reads a portable bitmap as input.  Creates a corresponding mask bitmap and writes it out. 

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
    pbmpaste < dest -and objmask <x> <y> | pbmpaste -or obj <x> <y>

For objects with a white background, you can either invert them or add a step:

    pbmmask obj > objmask
    pnminvert objmask | pbmpaste -and obj 0 0 > blackback
    pbmpaste < dest -and objmask <x> <y> | pbmpaste -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 graymaps and pixmaps, using the ppmarith tool.  For instance:

    ppmtopgm obj.ppm | pgmtopbm -threshold | pbmmask > objmask.pbm
    ppmarith -multiply dest.ppm objmask.pbm > t1.ppm
    pnminvert objmask.pbm | ppmarith -multiply obj.ppm - > t2.ppm
    ppmarith -add t1.ppm t2.ppm

An interesting variation on this is to pipe the mask through the ppmsmooth script before using it.  This makes the boundary between the two images less sharp. 

SEE ALSO

pbmpaste(1), pnminvert(1), pbm(5), ppmarith(1)

AUTHOR

Copyright (C) 1988 by Jef Poskanzer. 
 
Permission to use, copy, modify, and distribute this software and its documentation for any purpose and without fee is hereby granted, provided that the above copyright notice appear in all copies and that both that copyright notice and this permission notice appear in supporting documentation.  This software is provided "as is" without express or implied warranty.

Amiga Unix  —  Last change: 08 August 1989