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)
	MaxValue	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!
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