PBM Files

PBM is the portable bitmap format, a lowest common denominator monochrome file format. It was originally designed to make it reasonable to mail bitmaps between different types of machines. Now it serves as the common language of a large family of bitmap conversion filters. The definition is as follows:

A "magic number" for identifying the file type. A PBM file's magic number is the two characters "P1".
Whitespace (blanks, TABs, CRs, LFs).
A width, formatted as ASCII characters in decimal.
Whitespace.
A height, again in ASCII decimal.
Whitespace.
Width * height bits, each either '1' or '0', starting at the top-left corner of the bitmap, proceeding in normal English reading order.

The character '1' means black, '0' means white. Whitespace in the bits section is ignored. Characters from a "#" to the next end-of-line are ignored (comments). No line should be longer than 70 characters.

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:

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

The files are eight times smaller and many times faster to read and write.

EXAMPLE:

        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

PBM files are:

ASCII or BINARY
black and white
2D
No compression
1 image

Reference:

Programs to create a PBM file include:

Gnuplot
the MATHEMATICA command DISPLAY;

Programs to view a PBM file include:

The AVS module read_any_image can read a PBM file;
GIMP
The ImageVision program imgview can display a PBM file.
XV

Routines to read or write a PBM file:

PBMLIB, FORTRAN routines.
PBMPAK C routines

Programs to convert a PBM file to another format:

GIMP can read a PBM file and write out a copy in a variety of formats.
PBMTOASCII can read a PBM file and write out it out as ASCII graphics.
XV can read a PBM file and write out a copy in BMP, FIT, GIF, JPG, PGM/PM, RGB or TIF format.

Programs to convert a file to PBM format:

GIMP can read a file in a variety of formats, and write it out as a PBM file.
XV can read a file in a BMP, FIT, GIF, JPG, PGM/PPM, RGB or TIF format, and write it out as a PBM file.

Files you may copy:

feep.pbm, the example described above;
circle_ascii.pbm, a circle;

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Last revised on 10 May 2002.