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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)
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