ppmtopgm(1) - phpMan

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

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 quantiza-
tion 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 con-
verting 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), ppmtorgb3(1), rgb3toppm(1), ppmdist(1), ppm(1), pgm(1)

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 625 June 2017 Ppmtopgm User Manual(0)

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