1Ppmtopgm User Manual(0)                                Ppmtopgm User Manual(0)
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NAME

6       ppmtopgm - convert a PPM image to a PGM image
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SYNOPSIS

10       ppmtopgm
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12       [ppmfile]
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DESCRIPTION

16       This program is part of Netpbm(1).
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18       ppmtopgm reads a PPM as input and produces a PGM as output.  The output
19       is a "black and white" rendering of the original image, as in  a  black
20       and  white  photograph.   The quantization formula ppmtopgm uses is y =
21       .299 r + .587 g + .114 b.
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23       The dimensions and maxval of the output are  the  same  as  the  input.
24       Note  that  with only one color plane, there are far fewer brightnesses
25       that can be represented with the same  maxval  than  with  three  color
26       planes,  so  you  may  want  to  increase  the maxval of the input with
27       pamdepth before giving it to ppmtopgm to  avoid  loss  of  information.
28       For example, with a maxval of 1, there are 8 brightnesses that are pos‐
29       sible in a PPM (though some of them are  barely  distinguishable),  but
30       only 2 brightness levels possible in a PGM.
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32       Note that although there is a pgmtoppm program, it is not necessary for
33       simple conversions from pgm to ppm , because any ppm program  can  read
34       pgm  (and  pbm ) files automatically.  pgmtoppm is for colorizing a pgm
35       file.  Also, see ppmtorgb3 for a different way of converting  color  to
36       gray.   And ppmdist generates a grayscale image from a color image, but
37       in a way that makes it easy to differentiate the original  colors,  not
38       necessarily a way that looks like a black and white photograph.
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QUOTE

42       Cold-hearted orb that rules the night
43       Removes the colors from our sight
44       Red is gray, and yellow white
45       But we decide which is right
46       And which is a quantization error.
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SEE ALSO

50       pgmtoppm(1), ppmtorgb3(1), rgb3toppm(1), ppmdist(1), ppm(1), pgm(1)
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AUTHOR

54       Copyright (C) 1989 by Jef Poskanzer.
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DOCUMENT SOURCE

57       This  manual  page was generated by the Netpbm tool 'makeman' from HTML
58       source.  The master documentation is at
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60              http://netpbm.sourceforge.net/doc/ppmtopgm.html
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62netpbm documentation             625 June 2017         Ppmtopgm User Manual(0)
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