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       ppmtopgm - convert a portable pixmap into a portable graymap


       ppmtopgm [ppmfile]


       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.

       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)