pbm(5)                    FILE FORMATS                     pbm(5)



NAME
     pbm - portable bitmap file format

DESCRIPTION
     The portable bitmap format is a  lowest  common  denominator
     monochrome  file format.  It was originally designed to make
     it reasonable to mail bitmaps  between  different  types  of
     machines  using  the  typical stupid network mailers we have
     today.  Now it serves as the common language of a large fam-
     ily of bitmap conversion filters.  The definition is as fol-
     lows:

     - A "magic number" for identifying the  file  type.   A  pbm
       file's magic number is the two characters "P1".

     - Whitespace (blanks, TABs, CRs, LFs).

     - A width, formatted as ASCII characters in decimal.

     - Whitespace.

     - A height, again in ASCII decimal.

     - Whitespace.

     - Width * height bits, each either '1' or '0',  starting  at
       the  top-left  corner  of the bitmap, proceeding in normal
       English reading order.

     - The character '1' means black, '0' means white.

     - Whitespace in the bits section is ignored.

     - 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 bitmap in this format:
     P1
     # feep.pbm
     24 7
     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 1 1 1 1 0 0 1 1 1 1 0 0 1 1 1 1 0 0 1 1 1 1 0
     0 1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 1 0
     0 1 1 1 0 0 0 1 1 1 0 0 0 1 1 1 0 0 0 1 1 1 1 0
     0 1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0
     0 1 0 0 0 0 0 1 1 1 1 0 0 1 1 1 1 0 0 1 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  pos-
     sible, accepting anything that looks remotely like a bitmap.

     There is also a variant on the format, available by  setting
     the  RAWBITS  option  at compile time.  This variant is dif-
     ferent in the following ways:

     - The "magic number" is "P4" instead of "P1".

     - The bits are stored eight per byte, high bit first low bit
       last.

     - No whitespace is allowed in the bits section, and  only  a
       single  character  of  whitespace (typically a newline) is
       allowed after the height.

     - The files are eight times smaller and many times faster to
       read and write.

AUTHOR
     Copyright (C) 1989, 1991 by Jef Poskanzer.

























Sun Release 4.1  Last change: 27 September 1991                 2



