PBM(5)							      BSD File Formats Manual							    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 family of bitmap conversion filters.  The definition is as follows:

     o	 A "magic number" for identifying the file type.  A pbm file's magic number is the two characters "P1".
     o	 Whitespace (blanks, TABs, CRs, LFs).
     o	 A width, formatted as ASCII characters in decimal.
     o	 Whitespace.
     o	 A height, again in ASCII decimal.
     o	 Whitespace.
     o	 Width * height bits, each either '1' or '0', starting at the top-left corner of the bitmap, proceeding in normal English reading order.
     o	 The character '1' means black, '0' means white.
     o	 Whitespace in the bits section is ignored.
     o	 Characters from a "#" to the next end-of-line are ignored (comments).
     o	 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 possible, 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 different in the following
     ways:

     o	 The "magic number" is "P4" instead of "P1".
     o	 The bits are stored eight per byte, high bit first low bit last.
     o	 No whitespace is allowed in the bits section, and only a single character of whitespace (typically a newline) is allowed after the
	 height.
     o	 The files are eight times smaller and many times faster to read and write.

AUTHORS

     Copyright (C) 1989, 1991 by Jef Poskanzer.

BSD
								September 27, 1991							       BSD