NAME
    ppmtopgm - convert a portable pixmap into a portable graymap

SYNOPSIS
    ppmtopgm [ppmfile]

DESCRIPTION
    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.

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(5),pgm(5)

AUTHOR
    Copyright (C) 1989 by Jef Poskanzer.