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 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 automatically fall back on the slower but more
general plain format.
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 pgm(5)
jbigkit 2.0 - Generated Tue Nov 11 06:35:50 CST 2008