Reads a portable pixmap as input. Produces a portable graymap as out-
put. 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.
Note that although there is a pgmtoppm program, it is not necessary for
simple conversions from pgm to ppm , because any ppm program can read
pgm (and pbm ) files automatically. pgmtoppm is for colorizing a pgm
file. Also, see ppmtorgb3 for a different way of converting color to
gray. And 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.
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.
Copyright (C) 1989 by Jef Poskanzer.
10 April 2000 ppmtopgm(1)
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