ppmtopgm  -  convert  a  portable  pixmap  into a portable
       graymap


SYNOPSIS

       ppmtopgm [ppmfile]


DESCRIPTION

       Reads a portable pixmap as  input.   Produces  a  portable
       graymap as output.  The output is a "black and white" ren­
       dering of the original image, as in a black and white pho­
       tograph.  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  automati­
       cally.   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),ppm­
       torgb3(1),rgb3toppm(1),ppmdist(1),ppm(5),pgm(5)


AUTHOR

       Copyright (C) 1989 by Jef Poskanzer.


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