NAME

       ppmtopgm - convert a PPM image to a PGM image

SYNOPSIS

       ppmtopgm

       [ppmfile]

DESCRIPTION

       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 y = .299 r + .587 g + .114 b.

       The  dimensions  and  maxval of the output are the same as the input.  Note that with only
       one color plane, there are far fewer brightnesses that can be represented  with  the  same
       maxval  than  with three color planes, so you may want to increase the maxval of the input
       with pamdepth before giving it to ppmtopgm to avoid loss  of  information.   For  example,
       with  a  maxval  of 1, there are 8 brightnesses that are possible in a PPM (though some of
       them are barely distinguishable), but only 2 brightness levels possible in a PGM.

       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.

OPTIONS

       There are no command line options defined specifically for ppmtopgm, but it recognizes the
       options common to all programs based on libnetpbm (See
        Common Options ⟨index.html#commonoptions⟩ .)

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(1), pgm(1)

AUTHOR

       Copyright (C) 1989 by Jef Poskanzer.

DOCUMENT SOURCE

       This manual page was generated by the Netpbm tool 'makeman' from HTML source.  The  master
       documentation is at

              http://netpbm.sourceforge.net/doc/ppmtopgm.html