# pbmmask

Updated: 08 August 1989
Index

## NAME

pbmmask - create a mask bitmap from a regular bitmap

## SYNOPSIS

pbmmask [-expand] [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
        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 graymaps and pixmaps, using the pnmarith tool. For instance:

        ppmtopgm obj.ppm | pgmtopbm -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 the pnmsmooth script before using it. This makes the boundary between the two images less sharp.

## OPTIONS

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

## SEE ALSO

ppmcolormask, pnmpaste, pnminvert, pbm, pnmarith, pnmsmooth

## AUTHOR

Copyright (C) 1988 by Jef Poskanzer.

## Index

NAME
SYNOPSIS
DESCRIPTION
OPTIONS
SEE ALSO
AUTHOR