A QR code (an initialism for quick response code) is a type of matrix barcode (or two-dimensional barcode) invented in 1994 by the Japanese automotive company Denso Wave. QR codes are a popular type of two-dimensional barcode. They are also known as hardlinks or physical world hyperlinks. QR Codes store up to 4,296 alphanumeric characters of arbitrary text. This text can be anything, for example URL, contact information, a telephone number, even a poem! QR codes can be read by an optical device with the appropriate software. Such devices range from dedicated QR code readers to mobile phones.

A QR code consists of black squares arranged in a square grid on a white background, which can be read by an imaging device such as a camera, and processed using Reed–Solomon error correction until the image can be appropriately interpreted. The required data is then extracted from patterns that are present in both horizontal and vertical components of the image.

Error correction level - QR codes support four levels of error correction to enable recovery of missing, misread, or obscured data. Greater redundancy is achieved at the cost of being able to store less data. Here are the supported values:

• L - Allows recovery of up to 7% data loss
• M - Allows recovery of up to 15% data loss
• Q - Allows recovery of up to 25% data loss
• H - Allows recovery of up to 30% data loss

Margin - The width of the white border around the data portion of the code. This is in rows, not in pixels. (See below to learn what rows are in a QR code.)

Size - The size generated QR code in pixels.

QR codes are squares, with an equal number of rows and columns. There are a fixed set of QR code sizes: from 21 to 177 rows/columns, increasing in steps of four. Each configuration is called a version. The more rows/columns, the more data the code can store. Here is a summary of the versions:

• Version 1 has 21 rows and 21 columns, and can encode up to 25 alphanumeric characters
• Version 2 has 25 rows and 25 columns, and can encode up to 47 alphanumeric characters
• Version 3 has 29 rows and 29 columns, and can encode up to 77 alphanumeric characters
• ...
• Version 40 has 177 rows and 177 columns, and can encode up to 4,296 alphanumeric characters

Don’t confuse the number of rows and columns with size of the QR code image. The pixel size of the code is determined using data as usual.

The QR codes generator will determine which version to use, based on the amount of data you provide.

The appropriate QR code version will be returned depending on the number of characters you provide. For example, if you provide 55 alphanumeric characters, you will get a Version 3 QR code, although this can change if you specify an error correction (EC).

Before generating your QR code, consider what kind of device is used to read your code: the best QR code readers are able to read Version 40 codes; mobile devices might only be able to read up to Version 4.