Program allows ordinary digital camera to see round corners

By Ian Sample Science editor

Science may never tell us what lies round the next corner, but researchers have come up with the nearest thing: a computer program that turns a normal digital camera into a periscope.

In a demonstration of “computational periscopy” a US team at Boston University showed they could see details of objects hidden from view by analysing shadows they cast on a nearby wall.

Vivek Goyal, an electrical engineer at the university, said that while the work had clear implications for surveillance he hoped it would lead to robots that could navigate better and boost the safety of driverless cars.


He said: “I’m not especially excited by surveillance, I don’t want to be doing creepy things, but being able to see that there’s a child on the other side of a parked car, or see a little bit around the corner of an intersection could have a significant impact on safety.

The problem of how to see round corners has occupied modern researchers for at least a decade. And while scientists have made good progress in the field, the equipment used so far has been highly specialised and expensive.

In the latest feat, Goyal and his team used a standard digital camera and a mid-range laptop. “We didn’t use any sophisticated hardware. This is just an ordinary camera and we are all carrying these around in our pockets,” he said.

The researchers, writing in the journal Nature, describe how they pieced together hidden scenes by pointing the digital camera at the vague shadows they cast on a nearby wall. If the wall had been a mirror the task would have been easy, but a matt wall scatters light in all directions, so the reflected image is nothing but a blur. Goyal said: “In essence, computation can turn a matt wall into a mirror.”

They found that when an object blocked part of the hidden scene, their algorithms could use the combination of light and shade at different points on the wall to reconstruct what lay round the corner. In tests, the program pieced together hidden images of video game characters – including details such as their eyes and mouths – along with coloured strips and the letters “BU”.

Given the relative simplicity of the program and equipment, Goyal believes it could be possible for humans to learn the same trick. In a draft blog written for Nature, he said: “It is even conceivable for humans to be able to learn to see around corners with their own eyes; it does not require anything superhuman.”

At the moment, the program takes about 48 seconds to work out a hidden scene from a digital image, but Goyal believes it could be done much faster with more computer power. Eventually, it may be fast enough to run on video footage.

In an accompanying article, Martin Laurenzis, an imaging expert at the French–German Research Institute of Saint-Louis, explains that with multiple images to draw on, the technique could track the movement of hidden targets.

But it could also have much broader uses, he said, in microscopy, medical imaging and monitoring in hazardous environments such as chemical plants or nuclear power stations. Laurenzis said: “The technique could be used by vehicles to avoid collisions, and by firefighters and first responders to look into burning or collapsed structures.”