\
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.TH "Pbmmask User Manual" 1 "28 September 2021" "netpbm documentation"

.SH NAME

pbmmask - create a mask bitmap from a regular bitmap

.UN synopsis
.SH SYNOPSIS

\fBpbmmask\fP
[\fB-expand\fP]
[\fIpbmfile\fP]

.UN description
.SH DESCRIPTION
.PP
This program is part of
.BR "Netpbm" (1)\c
\&.
.PP
\fBpbmmask\fP reads a PBM image as input and generates a
corresponding mask of the foreground areas as another PBM image.
.PP
This is probably obsoleted by \fBpambackground\fP.
  
.PP
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.
.PP
This lets you do a masked paste like this, for objects with a black
background:

.nf
    pbmmask obj > objmask
    pnmpaste < dest -and objmask <x> <y> | pnmpaste -or obj <x> <y>

.fi

For objects with a white background, you can either invert them or
add a step:
.nf
    pbmmask obj > objmask
    pnminvert objmask | pnmpaste -and obj 0 0 > blackback
    pnmpaste < dest -and objmask <x> <y> | pnmpaste -or blackback <x> <y>

.fi

Note that this three-step version works for objects with black backgrounds
too, if you don't care about the wasted time.
.PP
You can also use masks with grayscale and color images, using the
\fIpnmarith\fP tool.  For instance:

.nf
    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

.fi

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

.UN options
.SH OPTIONS
.PP
In addition to the options common to all programs based on libnetpbm
(most notably \fB-quiet\fP, see 
.UR index.html#commonoptions
 Common Options
.UE
\&), \fBpbmmask\fP recognizes the following
command line option:


.TP
\fB-expand\fP
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 \fBpbmlife\fP program into a general
cellular automaton tool...)



.UN seealso
.SH SEE ALSO
.BR "pambackground" (1)\c
\&
.BR "ppmcolormask" (1)\c
\&,
.BR "pnmpaste" (1)\c
\&,
.BR "pnminvert" (1)\c
\&,
.BR "pnmarith" (1)\c
\&,
.BR "pnmsmooth" (1)\c
\&
.BR "pbm" (1)\c
\&,

.UN author
.SH AUTHOR

Copyright (C) 1988 by Jef Poskanzer.

.UN history
.SH HISTORY
.PP
\fBpbmmask\fP 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 \fBpambackground\fP.
.PP
It is likely that when Bryan wrote \fBpambackground\fP in 2006, he was
  unaware \fBpbmmask\fP existed.  Otherwise, he would presumably have
  replaced \fBpbmmask\fP with a wrapper around \fBpambackground\fP.
.SH DOCUMENT SOURCE
This manual page was generated by the Netpbm tool 'makeman' from HTML
source.  The master documentation is at
.IP
.B http://netpbm.sourceforge.net/doc/pbmmask.html
.PP