Bar codes, QR codes, and invisible QR codes

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QR codes have seen a massive development and adoption to solve slow input on a smartphone. The technology is closely related to fiducial marker augmented reality by encoding digital information in physical form. Barcodes and QR codes have been actively developed and deployed in the consumer market. Barcodes, which originally appeared in the 1970s, consist of vertical stripes that are read using a red pulsating laser light. These barcodes are now ubiquitous in most packaged products sold worldwide.

QR codes are an advancement over barcodes are QR codes. QR codes are patterns with black-and-white squares, which encode significantly more computer information than a barcode. Although they could also track inventory, their adoption for packaged products is limited. Instead, QR codes are used to trigger accessing information on a smartphone. A person points a smartphone to a QR code, which is recognized by a digital camera on the phone.

Several QR code technologies are currently employed. QR codes can be printed in ink or using invisible ink. The latter approach is fairly recent with notable examples:

Invisible QR codes 
Side by Side projector (uses infrared QR codes)

Another approach is to use pure vision recognition technologies instead of QR codes. Images features such as colour, edges, and patterns as seen in the photo are used for recognition. This approach is included in Fujitsu’s deployment and Qualcomm’s Gimbal SDK:

Fujitsu “invisible QR codes”
Gimbal Image Recognition

Given the two classes of QR codes, printed black-and-white markers and invisible codes, visible QR codes are more useful because they offer physical affordances. A person can see that the marker should be read by a smartphone and take the appropriate action. Invisible markers would need some way of telling the user that it has encoded digital information. The Fujitsu researchers agree that physical cues are needed so that the user can point his smartphone at the QR code.