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blender-deps/jbigkit-cmake/pbmtools/pgm.5

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+.TH pgm 5 "12 November 1991"
+.SH NAME
+pgm - portable graymap file format
+.SH DESCRIPTION
+The portable graymap format is a lowest common denominator grayscale
+file format.
+.IX "PGM file format"
+The definition is as follows:
+.IP - 2
+A "magic number" for identifying the file type.
+A pgm file's magic number is the two characters "P2".
+.IX "magic numbers"
+.IP - 2
+Whitespace (blanks, TABs, CRs, LFs).
+.IP - 2
+A width, formatted as ASCII characters in decimal.
+.IP - 2
+Whitespace.
+.IP - 2
+A height, again in ASCII decimal.
+.IP - 2
+Whitespace.
+.IP - 2
+The maximum gray value, again in ASCII decimal.
+.IP - 2
+Whitespace.
+.IP - 2
+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.
+.IP - 2
+Characters from a "#" to the next end-of-line are ignored (comments).
+.IP - 2
+No line should be longer than 70 characters.
+.PP
+Here is an example of a small graymap in this format:
+.nf
+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
+.fi
+.PP
+Programs that read this format should be as lenient as possible,
+accepting anything that looks remotely like a graymap.
+.PP
+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:
+.IX RAWBITS
+.IP - 2
+The "magic number" is "P5" instead of "P2".
+.IP - 2
+The gray values are stored as plain bytes, instead of ASCII decimal.
+.IP - 2
+No whitespace is allowed in the grays section, and only a single character
+of whitespace (typically a newline) is allowed after the maxval.
+.IP - 2
+The files are smaller and many times faster to read and write.
+.PP
+Note that this raw format can only be used for maxvals less than
+or equal to 255.
+If you use the
+.I 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.
+.SH "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)
+.SH AUTHOR
+Copyright (C) 1989, 1991 by Jef Poskanzer.
+.\" Permission to use, copy, modify, and distribute this software and its
+.\" documentation for any purpose and without fee is hereby granted, provided
+.\" that the above copyright notice appear in all copies and that both that
+.\" copyright notice and this permission notice appear in supporting
+.\" documentation.  This software is provided "as is" without express or
+.\" implied warranty.