Alphanumeric mode (which is 45 symbols: [A-Z0-9] and nine special symbols) is the only QR mode that's reliably supported among all scanner library implementatio

Alphanumeric mode (which is 45 symbols: [A-Z0-9] and nine special symbols) is the only QR mode that's reliably supported among all scanner library implementations (latin1 is part of the extended mode, Unicode & raw binary get detected with implementation-dependent heuristics). The encoding is great, actually: 4n bytes will get encoded into 6n alnums (base45 symbols) which are 3n * 11 = 33n QR-bits. A loss of just 3% (33/32 - 1). This works because [ alnum1 alnum2 ] by spec must get packed into [ 11 bits ] in the QR message bitstream. Wrote an explanation here: https://news.ycombinator.com/item?id=27592936 https://news.ycombinator.com/item?id=27592936