freebsd-nq/share/man/man5/pbm.5

.\"
.\" $FreeBSD$
.\"
.Dd September 27, 1991
.Dt PBM 5
.Sh NAME
.Nm pbm
.Nd portable bitmap file format
.Sh 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:
.Pp
.Bl -bullet -compact
.It
A "magic number" for identifying the file type.
A pbm file's magic number is the two characters "P1".
.It
Whitespace (blanks, TABs, CRs, LFs).
.It
A width, formatted as ASCII characters in decimal.
.It
Whitespace.
.It
A height, again in ASCII decimal.
.It
Whitespace.
.It
Width * height bits, each either '1' or '0', starting at the top-left
corner of the bitmap, proceeding in normal English reading order.
.It
The character '1' means black, '0' means white.
.It
Whitespace in the bits section is ignored.
.It
Characters from a "#" to the next end-of-line are ignored (comments).
.It
No line should be longer than 70 characters.
.El
.Pp
Here is an example of a small bitmap in this format:
.Bd -literal
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
.Ed
.Pp
Programs that read this format should be as lenient as possible,
accepting anything that looks remotely like a bitmap.
.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:
.Pp
.Bl -bullet -compact
.It
The "magic number" is "P4" instead of "P1".
.It
The bits are stored eight per byte, high bit first low bit last.
.It
No whitespace is allowed in the bits section, and only a single character
of whitespace (typically a newline) is allowed after the height.
.It
The files are eight times smaller and many times faster to read and write.
.El
.Sh AUTHORS
Copyright (C) 1989, 1991 by
.An Jef Poskanzer .
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