How QR Code Encoding Works
Definition: QR code encoding is the process of converting input data (text, URLs, numbers) into the binary matrix pattern of black and white modules that form a QR code.
QR codes support four encoding modes: Numeric (0-9, most efficient), Alphanumeric (0-9, A-Z, space, $%*+-./:), Byte (any character via UTF-8), and Kanji (Japanese characters). The encoder automatically selects the most efficient mode for the input data. A URL uses Byte mode, a phone number uses Numeric mode. The encoding process adds error correction data (Reed-Solomon codes) that enables scanning even when parts of the code are damaged.
Key points
- Four encoding modes for different data types
- Numeric mode: most efficient (3.3 bits/char)
- Byte mode: supports any UTF-8 character
- Reed-Solomon error correction built in
- Version 1 (21×21) to Version 40 (177×177)
- Automatic mode selection for optimal efficiency
Frequently asked questions
What encoding mode do URLs use?
URLs use Byte mode (Mode 4) because they contain lowercase letters, special characters, and mixed case — which aren't supported in Alphanumeric mode.
Why do some QR codes look denser than others?
More data requires more modules. A simple URL might use Version 3 (29×29 modules), while a vCard with full contact info might need Version 10 (57×57 modules).
Can QR codes store emoji?
Yes — emoji are encoded in Byte mode using UTF-8. However, they consume more capacity than plain ASCII text.
Related terms
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