3.2.2 PGM. Portable Grey-Map Format

See the man-page.

Plain version:

• Identifier "P2"
• ASCII representation of Width
• ASCII representation of Height
• ASCII representation of Maxvalue ($<$ $65536=2^{16}$)
• Height many lines of Width many pixels as ASCII words 0..Maxvalue separated by space

Raw version:

• Identifier "P5"
• ASCII representation of Width
• ASCII representation of Height
• ASCII representation of Maxvalue ($<$ $65536=2^{16}$)
• Height many lines of Width many pixels as one or two bytes from left to right and top to bottom