NAME¶

ppmtopgm - convert a PPM image to a PGM image

SYNOPSIS¶

ppmtopgm

[ppmfile]

DESCRIPTION¶

This program is part of Netpbm(1).

ppmtopgm 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 ppmtopgm uses is g = .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.

QUOTE¶

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.

SEE ALSO¶

pgmtoppm(1), ppmtorgb3(1), rgb3toppm(1), ppmdist(1), ppm(1), pgm(1)

AUTHOR¶

Copyright (C) 1989 by Jef Poskanzer.