man > ppmtopgm(1)

Ppmtopgm User Manual(1)                General Commands Manual               Ppmtopgm User Manual(1)

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 max‐
       val 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.   pgm‐
       toppm  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 ]8;;index.html#commonoptions\ Common Options]8;;\ .)


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

netpbm documentation                        25 June 2017                     Ppmtopgm User Manual(1)