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Ppmtopgm User Manual(0)                                Ppmtopgm User Manual(0)

       ppmtopgm - convert a PPM image to a PGM image



       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.

       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.

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

       Copyright (C) 1989 by Jef Poskanzer.

netpbm documentation             10 April 2000         Ppmtopgm User Manual(0)