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qr code
Encode
Generate from string
qrencode [--8bit] [--level H] --output qr.png "This is my text"
Decode
Decode from .png file
zbarimg -1 --raw -q -Sbinary qr.png
Decode from camera
zbarcam -1 --raw -Sbinary
There are four modes to encode data:
| Number | Mode | First 4 bits | Allowed characters |
|---|---|---|---|
| 1 | Numeric | 1 = 0b0001 | [0-9] |
| 2 | Alphanumeric (only uppercase letters) | 2 = 0b0010 | [0-9][A-Z], space, $, %, *, +, -, ., /, : |
| 3 | Byte encoding (8 bits) | 4 = 0b0100 | ISO/IEC 8859-1 |
| 4 | Kanji | 8 = 0b1000 | Shift JIS X 0208 |
qrencode will automatically decide which mode fits best. There is no way to specify numeric mode and fail if invalid letters are part of the encoded message. The only way to enforce a mode is to explicitly set –8bit.
There are four levels of error correction:
| Error Correction Level | Redundancy | error_correction_level number |
|---|---|---|
| Level L (Low) | 7% | 1 |
| Level M (Medium) | 15% | 0 |
| Level Q (Quartile) | 25% | 3 |
| Level H (High) | 30% | 2 |