pgm(5)		  Image	Format Library C++ Reference Manual		pgm(5)

NAME    [Toc]    [Back]

     pgm - portable graymap file format

DESCRIPTION    [Toc]    [Back]

     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 topleft
 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:




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pgm(5)		  Image	Format Library C++ Reference Manual		pgm(5)



     - 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    [Toc]    [Back]

     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    [Toc]    [Back]

     Copyright (C) 1989, 1991 by Jef Poskanzer.


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