\
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.TH "Ppmtopgm User Manual" 0 "10 April 2000" "netpbm documentation"

.UN lbAB
.SH NAME

ppmtopgm - convert a PPM image to a PGM image

.UN lbAC
.SH SYNOPSIS

\fBppmtopgm\fP

[\fIppmfile\fP]

.UN lbAD
.SH DESCRIPTION
.PP
This program is part of
.BR Netpbm (1)
.
.PP
\fBppmtopgm\fP reads a PPM as input and produces a PGM as output.
The output is a 'black and white' rendering of the original
image, as in a black and white photograph.  The quantization formula
\fBppmtopgm\fP uses is g = .299 r + .587 g + .114 b.
.PP
Note that although there is a \fBpgmtoppm\fP program, it is not
necessary for simple conversions from pgm to ppm , because any ppm
program can read pgm (and pbm ) files automatically.  \fBpgmtoppm\fP
is for colorizing a pgm file.  Also, see \fBppmtorgb3\fP for a
different way of converting color to gray.  And \fBppmdist\fP
generates a grayscale image from a color image, but in a way that
makes it easy to differentiate the original colors, not necessarily a
way that looks like a black and white photograph.

.UN lbAE
.SH QUOTE

.nf
Cold-hearted orb that rules the night
Removes the colors from our sight
Red is gray, and yellow white
But we decide which is right
And which is a quantization error.
.fi

.UN lbAF
.SH SEE ALSO
.BR pgmtoppm (1)
,
.BR ppmtorgb3 (1)
,
.BR rgb3toppm (1)
,
.BR ppmdist (1)
,
.BR ppm (5)
,
.BR pgm (5)


.UN lbAG
.SH AUTHOR

Copyright (C) 1989 by Jef Poskanzer.