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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, accept-
     ing 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 char-
	 acter 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

NAME | DESCRIPTION | AUTHORS

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