QR code: structure and how it works

In short: The QR code is a square 2D code of black and white modules. It was developed by Denso Wave in 1994 for the car industry and holds data with built-in error correction.

In more detail: Three large squares in the corners (finder patterns) show the reader position and rotation. Alignment patterns, timing patterns and format information are added. The data is protected with Reed-Solomon error correction, so the code can still be read when part is damaged or covered.

In detail

• Size: versions 1 to 40 (21×21 to 177×177 modules).
• Error correction: levels L (about 7%), M (15%), Q (25%), H (30%). Higher level = more redundancy, less data.
• Modes: numeric, alphanumeric, byte, kanji.
• Content: URLs, text, Wi-Fi access, contacts, payments (EPC QR / GiroCode), tickets.
• Mask: a pattern is laid over the data so that no large single-colour areas appear.
• Security: QR codes can lead to phishing sites (“quishing”). Check the target before opening.
• Dynamic: the code points to a short link whose target can be changed later.

See also: Barcode types at a glance, Barcode scanners: technology and types