We encounter QR codes everywhere—square barcodes used on advertisements, business cards, and even in social media. With the quick scan of a cell phone picture, we can load a URL, a logo, or a set of contact information—with a good image, that is. Too far from the QR code, the phone cannot capture a clear image; too close, and it will not be able to capture the whole code. QR codes are an all-or-nothing way of relaying information: without good viewing conditions, observers cannot receive any of the data messages encoded in the QR code image.
Enter Strata, a new encoding method developed by Assistant Professor of Electrical Engineering Wenjun Hu and her team. Strata, like the QR code, is a type of barcode. Its images are comprised of black and white pixel patterns encoded with information, denoting a few hundred characters of text or a URL. But unlike QR codes, Strata images have more flexibility: observers do not need ideal viewing conditions to gain at least some information from the code.
“In Times Square, for example, you have a big billboard, and you have people from all sorts of distances and directions,” said Hu. On that billboard is a standard QR code, but to get information from that code, observers need to be able to perceive it clearly. They may need to move closer to the code, adjust their viewing angle, or use a higher-resolution phone camera. “Even if they get closer or further, can they still see something? This is the basic motive behind Strata,” Hu said.
At a glance, a Strata code looks a lot like a QR code: both are squares with patterns of black and white pixels. However, a Strata code has multiple “layers”—different images formed by the pixels, depending on how well the observer can see the code. To an observer standing across the street from a Strata image, the upper left-hand corner might appear to be white, while the rest of the image might appear to be black. The overall Strata image as perceived from across the street might be the code’s first layer. But when the observer stands directly in front of the Strata code and can perceive all of the individual black and white pixels arranged throughout the image, she sees a more complicated pattern—another layer of the code. The more intricate the layer of the Strata code, the more information it can store, since a more complex pattern of pixels can be encoded with more data. For example, the layer visible from far away might denote a company’s trademark, but when the observer steps closer, a more complex layer might provide the company’s name, and a third layer could then contain the company’s address.
Multi-layered Strata codes present new challenges for engineers. So that code layers can be discerned even from far away, engineers must be sure not to allow too much interference—finer black and white layers that disrupt the overall images of more coarse layers—so that the multiple levels of Strata codes can be read as clearly as possible. Since engineers are limited in the amount of information that they can encode in each layer of the Strata code, they must also keep in mind these encoding parameters, or accept the trade-off of a larger code to include more data.
Strata’s encoding flexibility does come at a cost. Since Strata codes are designed to have multiple clear layers, they are more limited than QR codes in which patterns they can present, and therefore in how much information they can hold. “Right now, if you have the same resolution at different layers, we can get about two thirds of the capacity of a QR code of the same size and resolution,” Hu said.
Despite this capacity caveat, Strata codes enhance the capabilities of barcodes for advertisers and other everyday users. Although further research is necessary to maximize the amount of information that can be encoded in each layer, Strata offers flexibility that could make barcodes more accessible to observers in non-ideal settings. The hope is to pique observers’ curiosity so that they’ll adjust their viewing conditions for more information.
“Of course, there’s going to be a trade-off—you can’t get everything,” Hu said. “But something is better than nothing.”