QR Code (Quick Response Code)
A QR code is a two-dimensional matrix code that stores information such as URLs, text, and contact data and can be scanned quickly by cameras and scanners.
๐ณ Basic Structure and Characteristics
A QR code represents data using black and white modules arranged in a square matrix. Compared to 1D barcodes, QR codes provide higher density and built-in error correction.
Key Components
- ๐ Position detection patterns: three large markers used to detect orientation and position.
- ๐ Timing patterns: lines that help determine the module grid.
- ๐ Format information: stores error correction level and mask pattern.
- ๐ Data area: contains encoded data and error correction codewords.
๐ข Versions and Capacity
QR codes have versions numbered 1โ40; larger versions increase the number of modules and data capacity.
Capacity considerations
Capacity depends on encoding mode (numeric, alphanumeric, byte, kanji) and error correction level. Numeric mode holds the most digits; byte mode holds arbitrary bytes.
๐ค Encoding Modes
QR codes support multiple encoding modes to efficiently convert data into bitstreams depending on content type.
Common modes
- โ๏ธ Numeric: digits 0โ9 (highest density).
- โ๏ธ Alphanumeric: digits, uppercase letters, space and some symbols.
- โ๏ธ Byte: arbitrary byte sequences (e.g., UTF-8).
- โ๏ธ Kanji: efficient encoding for Shift JIS Kanji (used for Japanese text).
๐ก๏ธ Error Correction (ECC)
QR codes use ReedโSolomon based error correction which allows recovery from damage or obscuration of modules.
Levels
- ๐ L (~7%): low redundancy, more capacity.
- ๐ M (~15%): medium level, a common default.
- ๐ Q (~25%): higher redundancy.
- ๐ H (~30%): highest redundancy for damaged labels.
โ๏ธ Generation and Implementation
QR codes can be generated by many libraries and online tools; server-side and client-side implementations are widely available.
Popular libraries
- ๐ PHP: chillerlan/php-qrcode, endroid/qr-code
- ๐ JavaScript: qrcode.js, QRCode.js
- ๐ Python: qrcode, segno
Practical tips
Set an appropriate error correction level and margin, ensure sufficient print/display size and contrast, and test under expected scanning conditions.
โ ๏ธ Security and Operational Considerations
While QR codes are data carriers, they can be abused to direct users to malicious resources. Consider UX and safeguards.
Mitigations
- ๐ Show full URL previews in scanner apps before opening.
- ๐ Label shortened URLs clearly.
- ๐ Include issuer information on printed materials.
๐ก Typical Use Cases
Common scenarios include website links, ticketing, payments, contact (vCard), WiโFi credentials, and offline interactions.