What is QR code?

QR code is a popular two-dimensional barcode developed by the Japanese company Denso-Wave in 1994, which is offered to the public for free. Its designation QR means Quick Response, because it is quickly readable and decoded. It has much more capacity to store information compared to the universal product barcode used to mark trade items all over the world. Only text information can be stored in QR codes, e.g. GPS coordinates, internet-banking payment orders, and contact or website addresses.

The principle of this technology lies in a specific algorithm that encodes the text information into the square-shaped black and white image (or other colour combination), which can then be printed or shared on the internet. QR code readers are machines, mostly cell phones, which have a software to read the QR code via their cameras and display the encoded text.

There are several options which can influence the final QR image:

Redundancy

QR codes, or QR images, are designed to maintain the information's integrity by means of error correction, or redundancy. This means that the code can be fully readable, even when a part of it is damaged or misprinted. The higher the error correction level used to encode the information, the more "damage" the QR code can sustain. In general, there are four levels of error correction: L – low; M – medium; Q – quartile; and H – high. These can restore from 7% (low level) up to 30% (high level) of codewords. To its disadvantage, higher redundancy also decreases the storage capacity and increases the "density" of the QR code.

Size

And what about the size of the QR code? Going extreme in either direction, too large or small, can cause scanning issues. Be sure to check what size works best for the media you're using.

Image format

QR codes can be stored in various digital image formats that supports lossless data compression, like PNG. The most common JPEG (or JPG) format is not recommended because it uses loose compression of the encoded data that can lead to the blur or smear effect and make it less readable. The best way to store the information is to save the QR code in vector graphic file formats, like SVG. SVG images are fully resizable (virtually infinitely) without the loss of quality.

Colours

The colours of QR codes can also be altered, but an appropriate contrast between the foreground and background colour is necessary for the best readability.