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