.TH ppmcolormask 1 "14 April 2000"
.IX ppmcolormask
.SH NAME
ppmcolormask - produce mask of areas of a certain color in a PPM file
.SH SYNOPSIS
.B ppmcolormask
.I color
.RI [ ppmfile ]
.SH DESCRIPTION
Reads a PPM file as input.  Produces a PBM (bitmap) file as output.
The output file is the same dimensions as the input file and is black in
all places where the input file is the color 
.IR color ,
and white everywhere else.  

The output of 
.B ppmcolormask
is useful as an alpha mask input to
.BR pnmcomp .
Note that you can generate such an alpha mask automatically as you convert
to PNG format with
.BR pnmtopng (1).
Use its 
.B -transparent
option.

.I ppmfile
is the input file.  If you don't specify 
.IR ppmfile ,
the input is from Standard Input.

The output goes to Standard Output.

You can specify 
.I color
five ways:
.IX "specifying colors"
.TP 
o
An X11-style color name (e.g. 
.BR black ).
.TP 
o 
An X11-style hexadecimal specifier: rgb:r/g/b, where r g and b are
each 1- to 4-digit hexadecimal numbers.
.TP 
o
An X11-style decimal specifier: rgbi:r/g/b, where r g and b are
floating point numbers between 0 and 1.
.TP 
o 
For backwards compatibility, an old-X11-style hexadecimal number:
#rgb, #rrggbb, #rrrgggbbb, or #rrrrggggbbbb.
.TP 
o 
For backwards compatibility, a triplet of numbers separated by
commas: r,g,b, where r g and b are floating point numbers between 0
and 1.  (This style was added before MIT came up with the similar rgbi
style.)

.SH "SEE ALSO"
.BR pgmtoppm (1), 
.BR pnmcomp (1),
.BR pbmmask (1),
.BR ppm(5)

.SH AUTHOR
Bryan Henderson (bryanh@giraffe-data.com)
\" Contributed to the public domain.
