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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)