1Ppmtopgm User Manual(0) Ppmtopgm User Manual(0)
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6 ppmtopgm - convert a PPM image to a PGM image
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10 ppmtopgm
11 [ppmfile]
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16 This program is part of Netpbm(1).
17 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.
22 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.
31 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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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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50 pgmtoppm(1), ppmtorgb3(1), rgb3toppm(1), ppmdist(1), ppm(1), pgm(1)
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54 Copyright (C) 1989 by Jef Poskanzer.
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57 This manual page was generated by the Netpbm tool 'makeman' from HTML
58 source. The master documentation is at
59 http://netpbm.sourceforge.net/doc/ppmtopgm.html
61netpbm documentation 625 June 2017 Ppmtopgm User Manual(0)