/share/man/man5/pbm.5
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- .\"
- .\" $FreeBSD$
- .\"
- .Dd September 27, 1991
- .Dt PBM 5
- .Os
- .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 .
- .\" Permission to use, copy, modify, and distribute this software and its
- .\" documentation for any purpose and without fee is hereby granted, provided
- .\" that the above copyright notice appear in all copies and that both that
- .\" copyright notice and this permission notice appear in supporting
- .\" documentation. This software is provided "as is" without express or
- .\" implied warranty.