QR code

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A QR code (quick-response code) is a type of two-dimensional matrix barcode.Japanese company Denso Wave invented in in 1994 for labelling automobile parts.

A QR code consists of a square, which contains other elements. There are black squates, which are arranged in a grid. Some of the parts are not filled, usually they are white. Some parts of the code are markers. These markers help with reading and decoding the information. Usually, the code is read by an imaging device, such as a camera. The information in the image is then decoded.

QR codes have Reed–Solomon error correction. This means that even if parts of the code cannot be decoded, or they are wrong, the code can still be used.

The required data are then extracted from patterns that are present in both the horizontal and the vertical components of the QR image.

In many ways, QR codes are similar to barcodes. They can hold more information, and they also can hold different types of information:

• Numeric information: they can store numbers
• Alphanumeric information: They can store letters
• Binary information: Raw data
• Kanji

Compared to the standard barcodes, QR codes were used beyond labelling car parts because the image can be read more quickly, and because more information can be stored. Applications include product tracking, identifying an item, tracking time, document management, and general marketing.

Whereas a barcode is a machine-readable optical image that contains information specific to the labelled item, the QR code contains the data for a locator, an identifier, and for web-tracking. To efficiently store data, QR codes use four standardized modes of encoding: (i) numeric, (ii) alphanumeric, (iii) byte or binary, and (iv) kanji. Compared to standard UPC barcodes, the QR labelling system was applied beyond the automobile industry because of faster reading of the optical image and greater data-storage capacity in applications such as product tracking, item identification, time tracking, document management, and general marketing.

Information capacity

The amount of data that can be represented by a QR code symbol depends on the data type (mode, or input character set), version (1, ..., 40, indicating the overall dimensions of the symbol, i.e. 4 × version number + 17 dots on each side), and error correction level. The maximum storage capacities occur for version 40 and error correction level L (low), denoted by 40-L:

Maximum character storage capacity (40-L)
Character refers to individual values of the input mode (data type).

Input mode	Max. characters	Bits/char.	Possible characters, default encoding
Numeric only	7,089	3​1⁄3	0, 1, 2, 3, 4, 5, 6, 7, 8, 9
Alphanumeric	4,296	5​1⁄2	0–9, A–Z (upper-case only), space, $, %, *, +, -, ., /, :
Binary/byte	2,953	8	ISO/IEC 8859-1
Kanji/kana	1,817	13	Shift JIS X 0208

Here are some samples of QR codes:

• 
  Version 1 (21×21). Content: "Ver1"
• 
  Version 2 (25×25). Content: "Version 2"
• 
  Version 3 (29×29). Content: "Version 3 QR Code"
• 
  Version 4 (33×33). Content: "Version 4 QR Code, up to 50 char"
• 
  Version 10 (57×57). Content: "VERSION 10 QR CODE, UP TO 174 CHAR AT H LEVEL, WITH 57X57 MODULES AND PLENTY OF ERROR CORRECTION TO GO AROUND. NOTE THAT THERE ARE ADDITIONAL TRACKING BOXES" (actually encoded in all capital letters). (Tracking boxes are more commonly called alignment patterns.)
• 
  Version 25 (117×117) Content: 1,269 characters of ASCII text describing QR codes
• 
  Version 40 (177×177) Content: "Version 40 QR Code can contain up to 1852 chars ..." (and followed by four paragraphs of ASCII text describing QR codes). The text refers to a QR Code with a "Level H" error correction. Other levels provide higher capacity.