pgm(5) pgm(5)
NAME
pgm - portable graymap file format
DESCRIPTION
The portable graymap format is a lowest common denominator
grayscale file format. The definition is as follows:
- A "magic number" for identifying the file type. A pgm
file's magic number is the two characters "P2".
- Whitespace (blanks, TABs, CRs, LFs).
- A width, formatted as ASCII characters in decimal.
- Whitespace.
- A height, again in ASCII decimal.
- Whitespace.
- The maximum gray value, again in ASCII decimal.
- Whitespace.
- Width * height gray values, each in ASCII decimal,
between 0 and the specified maximum value, separated by
whitespace, starting at the top-left corner of the
graymap, proceeding in normal English reading order. A
value of 0 means black, and the maximum value means
white.
- Characters from a "#" to the next end-of-line are
ignored (comments).
- No line should be longer than 70 characters.
Here is an example of a small graymap in this format:
P2
# feep.pgm
24 7
15
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 3 3 3 3 0 0 7 7 7 7 0 0 11 11 11 11 0 0 15 15 15 15 0
0 3 0 0 0 0 0 7 0 0 0 0 0 11 0 0 0 0 0 15 0 0 15 0
0 3 3 3 0 0 0 7 7 7 0 0 0 11 11 11 0 0 0 15 15 15 15 0
0 3 0 0 0 0 0 7 0 0 0 0 0 11 0 0 0 0 0 15 0 0 0 0
0 3 0 0 0 0 0 7 7 7 7 0 0 11 11 11 11 0 0 15 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Programs that read this format should be as lenient as
possible, accepting anything that looks remotely like a
graymap.
There is also a variant on the format, available by
12 November 1991 1
pgm(5) pgm(5)
setting the RAWBITS option at compile time. This variant
is different in the following ways:
- The "magic number" is "P5" instead of "P2".
- The gray values are stored as plain bytes, instead of
ASCII decimal.
- No whitespace is allowed in the grays section, and only
a single character of whitespace (typically a newline)
is allowed after the maxval.
- The files are smaller and many times faster to read and
write.
Note that this raw format can only be used for maxvals
less than or equal to 255. If you use the pgm library and
try to write a file with a larger maxval, it will automat-
ically fall back on the slower but more general plain for-
mat.
SEE ALSO
fitstopgm(1), fstopgm(1), hipstopgm(1), lispmtopgm(1),
psidtopgm(1), rawtopgm(1), pgmbentley(1), pgmcrater(1),
pgmedge(1), pgmenhance(1), pgmhist(1), pgmnorm(1),
pgmoil(1), pgmramp(1), pgmtexture(1), pgmtofits(1),
pgmtofs(1), pgmtolispm(1), pgmtopbm(1), pnm(5), pbm(5),
ppm(5)
AUTHOR
Copyright (C) 1989, 1991 by Jef Poskanzer.
12 November 1991 2
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