QR Code is a frequently-used two dimensional symbol which is in the shape of a regular square. In detail, the regular square is made up of an encoding region and four function patterns which are called finder, separator, timing patterns, and alignment patterns respectively.

Apparently, the encoding region is used to encode the valid data of QR Code. But what are the functions of the other four function patterns of QR Code? Are they necessary?

In a QR Code barcode, there are three finder patterns in total and they are the same as each other. As for position, these three finder patterns are placed at the upper left, upper right and lower left corners of the barcode image respectively. Each finder pattern is in the shape of three superimposed concentric squares and consists of dark 7*7 modules, light 5*5 modules and dark 3*3 modules. Additionally, the ratio of module widths in a finder pattern is 1:1:3:1:1. The main function of the finder patterns is to unambiguously define the location and rotational orientation of the symbol in the field of view.

A separator consists of all light modules and is of one-module width. It is located between each finder pattern and the encoding region. So its main function is to separate the function patterns and the encoding region.

Each QR Code has two timing patterns: horizontal pattern and vertical pattern. They are made up of a one module wide row or column of alternating dark and light modules, starting and ending with a dark module. The vertical timing pattern runs down column 6 of the symbol between the separators for the left-hand finder patterns while the horizontal timing pattern runs across row 6 of the symbol between the separators for the upper finder patterns. The main function of timing patterns is to enable the symbol density and version to be decided and supply datum positions for determining module coordinates.

Alignment patterns are available only in QR Code symbols of version 2 or larger. Each alignment pattern can be viewed as three superimposed concentric squares, made up of dark 5*5 modules, light 3*3 modules and a single central dark module. What's more, the number of alignment patterns may be different and it can be determined by the symbol version.