3.2.1 PBM. Portable Bit-Map Format

See the man-page.

Plain version:

• Identifier "P1"
• ASCII representation of Width
• ASCII representation of Height
• Height many lines of Width many pixels as ASCII characters separated by space.

Raw version:

• Identifier "P4"
• ASCII representation of Width
• ASCII representation of Height
• Height many lines of Width many pixels (8 pixel packed in one byte, padded at end of line) from left to right and top to bottom (high bit first)
• This uses 2byte=16bit/pixel.