CentOS 5.2

GNU/Linux	CentOS 5.2
	pbm(1)

pbm

Updated: 03 October 2003
Table Of Contents

NAME

pbm - Netpbm bi-level image format

DESCRIPTION

This program is part of Netpbm.

The PBM format is a lowest common denominator monochrome file format. It
serves as the common language of a large family of bitmap image conversion
filters. Because the format pays no heed to efficiency, it is simple and
general enough that one can easily develop programs to convert to and from
just about any other graphics format, or to manipulate the image.

The name "PBM" is an acronym derived from "Portable Bit Map."

This is not a format that one would normally use to store a file or to
transmit it to someone -- it’s too expensive and not expressive enough for
that. It’s just an intermediary format. In it’s purest use, it lives only in
a pipe between two other programs.

The format definition is as follows.

A PBM file consists of a sequence of one or more PBM images. There are no
data, delimiters, or padding before, after, or between images.

Each PBM image consists of the following:
1. A "magic number" for identifying the file type. A pbm image’s magic
number is the two characters "P4".
2. Whitespace (blanks, TABs, CRs, LFs).
3. The width in pixels of the image, formatted as ASCII characters in
decimal.
4. Whitespace.
5. The height in pixels of the image, again in ASCII decimal.
6. Newline or other single whitespace character.
7. A raster of Height rows, in order from top to bottom. Each row is Width
bits, packed 8 to a byte, with don’t care bits to fill out the last byte
in the row. Each bit represents a pixel: 1 is black, 0 is white. The
order of the pixels is left to right. The order of their storage within
each file byte is most significant bit to least significant bit. The
order of the file bytes is from the beginning of the file toward the end
of the file.
A row of an image is horizontal. A column is vertical. The pixels in the
image are square and contiguous.
8. Characters from a "#" to the next end-of-line, before the width/height
line, are comments and are ignored.

There is actually another version of the PBM format, even more more
simplistic, more lavishly wasteful of space than PBM, called Plain PBM.
Plain PBM actually came first, but even its inventor couldn’t stand its
recklessly squanderous use of resources after a while and switched to what
we now know as the regular PBM format. But Plain PBM is so redundant -- so
overstated -- that it’s virtually impossible to break. You can send it
through the most liberal mail system (which was the original purpose of the
PBM format) and it will arrive still readable. You can flip a dozen random
bits and easily piece back together the original image. And we hardly need
to define the format here, because you can decode it by inspection.

The difference is:
-
There is exactly one image in a file.
-
The "magic number" is "P1" instead of "P4".
-
Each pixel in the raster is represented by a byte containing ASCII
’1’ or ’0’, representing black and white respectively. There are no
fill bits at the end of a row.
-
White space in the raster section is ignored.
-
You can put any junk you want after the raster, if it starts with a
white space character.
-
No line should be longer than 70 characters.

Here is an example of a small image in the plain PBM 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

There is a newline character at the end of each of these lines.

You can generate the Plain PBM format from the regular PBM format (first
image in the file only) with the pnmtoplainpnm program.

Programs that read this format should be as lenient as possible, accepting
anything that looks remotely like a bitmap.

COMPATIBILITY

Before July 2000, there could be at most one image in a PBM file. As a
result, most tools to process PBM files ignore (and don’t read) any data
after the first image.

GNU/Linux man pages

Livre :
Expressions régulières,
Syntaxe et mise en oeuvre :

ISBN : 978-2-7460-9712-4
EAN : 9782746097124
(Editions ENI)

GNU/Linux

pbm(1)