DaubNET: File Formats Collection: PBM

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Table of Contents

Basic Description
Basic File Format

Raster Data Encoding

Portability
Trademarks, Patents and Royalties
Cross Checking Software
Resources

Online
Paper

Disclaimer

Last updated: May 18. 2000

Basic Description

PBMs, PGMs and PPMs are a family of bitmap formats, where PBMs store black&white images, PGMs store grayscale images and PPMs store color images.

Basic File Format

Since PGMs are not binary files (as most other bitmap formats), but ASCII files, "fields" are not determined by a length in bytes, but seperated by whitespace. Note that there can be comments, which are considered as whitespace, and that no line should be longer than 70 characters. The CRs and LFs in the file do not have to correspond to the end of a pixel row.

Name			Description
Header
	Signature		2 byte format signature: "P1" (ASCII codes 80 and 49): PBM ASCII black&white "P2" (ASCII codes 80 and 50): PGM ASCII grayscale "P3" (ASCII codes 80 and 51): PPM ASCII colored "P4" (ASCII codes 80 and 52): PBM RAW black&white "P5" (ASCII codes 80 and 53): PGM RAW grayscale "P6" (ASCII codes 80 and 54): PPM RAW colored
	(Whitespace)
	Width		Bitmap Width
	(Whitespace)
	Height		Bitmap Height
	Data Precision		present in PGM and PPM files, but not in PBM
		(Whitespace)	PBM: not present PGM: Value to be considered as white. PPM: Value to be considered as max. for all three color components. This value needs to be >0, and can be >255 if in ASCII format!
		MaxValue
Raster Data Block			see below

Definition of
- Whitespace: one or more characters from the following set: TAB, LF, CR, SPACE. (= ASCII codes: 8, 10, 13, 32)
- Comment: The caracter "#" (ASCII code 35) followed by any number of characters, up to a LF or CR.

Raster Data encoding

PBM ASCII black & white. (Signature=P1)

Name			Description
		(Whitespace)
		Pixel	ASCII pixel. 0 (ASCII 48) =white, 1 (ASCII 49) = black.
	repeated Width times
repeated Height times

PGM ASCII grayscale. (Signature=P2)

Name			Description
		(Whitespace)
		Pixel	A pixel's gray value. Must be between 0 and Header.MaxValue
	repeated Width times
repeated Height times

PPM ASCII color. (Signature=P3)

Name			Description
		(Whitespace)
		Pixel Red	A pixel's red component Must be between 0 and Header.MaxValue
		(Whitespace)
		Pixel Green	A pixel's green component Must be between 0 and Header.MaxValue
		(Whitespace)
		Pixel Blue	A pixel's blue component Must be between 0 and Header.MaxValue
	repeated Width times
repeated Height times

PBM RAW black & white. (Signature=P4)

There cannot be any whitespace or comments in between pixels, as they would be interpreted as pixels.

Name		Size	Description
Seperator		1 byte	A single byte of whitespace (preferably a LF) that seperates MaxValue from the Pixel data
	PixelData	1 byte	A single byte with the pixel data for 8 pixels. Within each byte every bit represents one pixel
		1 bit (bit 7)	leftmost pixel
		...
		1 bit (bit 0)	rightmost pixel. Pixels wrap along lines, so this pixel could already actualy be on then next line.
repeated (Width*Height+7) div 8 times. (where div is integer division)

PGM RAW grayscale. (Signature=P5)

There cannot be any whitespace or comments in between pixels, as they would be interpreted as pixels. MaxValue cannot be more than 255.

Name			Size	Description
Seperator			1 byte	A single byte of whitespace (preferably a LF) that seperates MaxValue from the Pixel data
		Pixel	1 byte	A single byte with the pixel's gray value.
	repeated Width times
repeated Height times

PPM RAW color. (Signature=P6)

There cannot be any whitespace or comments in between pixels, as they would be interpreted as pixels. MaxValue cannot be more than 255.

Name			Size	Description
Seperator			1 byte	A single byte of whitespace (preferably a LF) that seperates MaxValue from the Pixel data
		Red	1 byte	A single byte with the pixel's red component.
		Green	1 byte	A single byte with the pixel's green component.
		Blue	1 byte	A single byte with the pixel's blue component.
	repeated Width times
repeated Height times

Example:

A grayscale bitmap with 24x7 pixels, where 15 is white (equivalent to 5 bits color depth)

P2
# feep.pgm
24 7
15
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 3 3 3 3 0 0 7 7 7 7 0 0 11 11 11 11 0 0 15 15 15 15 0
0 3 0 0 0 0 0 7 0 0 0 0 0 11 0 0 0 0 0 15 0 0 15 0
0 3 3 3 0 0 0 7 7 7 0 0 0 11 11 11 0 0 0 15 15 15 15 0
0 3 0 0 0 0 0 7 0 0 0 0 0 11 0 0 0 0 0 15 0 0 0 0
0 3 0 0 0 0 0 7 7 7 7 0 0 11 11 11 11 0 0 15 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

Portability

The PGM format was designed with portability in mind (hence it's name), and is therefore easy to implement on any platform. When reading PGMs one should make as few assumptions as possible, for example expect more than 70 characters per line.

Trademarks, Patents and Royalties

None known.
(please read the disclaimer)

Cross-Checking Software

This section is for programmers, who wish to cross-check their implementation with others. This is an incomplete list of programs, which are available as freeware / shareware / try-before-buy etc.

The following software is able to decode PBMs, PGMs and PPMs:

The following software is able to encode PBMs, PGMs and PPMs

Online Resources

Paper Resources

Disclaimer

This is not the official format documentation. Although we're doing our best to keep this information as accurate as possible, there is no way of checking all of it under all possible circumstances. We're not taking any responsibility for the results of this information or lack thereof. The 'trademarks, patents and royalties' section is here just for your convenience, and is in no way complete. Please send us a note, if you find any incorrect of missing information to fileformats@daubnet.com.