.TH ppmtopgm 1 "10 April 2000"
.IX ppmtopgm
.SH NAME
ppmtopgm - convert a portable pixmap into a portable graymap
.SH SYNOPSIS
.B ppmtopgm
.RI [ ppmfile ]
.SH DESCRIPTION
Reads a portable pixmap as input.  Produces a portable graymap as
output.  The output is a "black and white" rendering of the original
image, as in a black and white photograph.  The quantization formula
used is .299 r + .587 g + .114 b.
.PP
Note that although there is a
.B pgmtoppm
program, it is not necessary for simple conversions from pgm to ppm ,
because any ppm program can read pgm (and pbm ) files automatically.
.B pgmtoppm
is for colorizing a pgm file.  Also, see
.B ppmtorgb3
.IX ppmtorgb3
for a different way of converting color to gray.  And 
.B ppmdist 
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.

.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
.SH "SEE ALSO"
.BR pgmtoppm (1), ppmtorgb3 (1), rgb3toppm (1), ppmdist (1), ppm (5), pgm (5)
.SH AUTHOR
Copyright (C) 1989 by Jef Poskanzer.
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