pgm(5) — Dell System V Release 4 Issue 2.2



pgm(5)                  UNIX System V(12 November 1991)                  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:



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pgm(5)                  UNIX System V(12 November 1991)                  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
      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.






























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