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While vacationing on the coast of Spain in 2012, the computer vision scientist Antonio Torralba noticed stray shadows on the wall of his hotel room that didn’t seem to have been cast by anything. Torralba eventually realized that the discolored patches of wall weren’t shadows at all, but rather a faint, upside-down image of the patio outside his window. The window was acting as a pinhole camera — the simplest kind of camera, in which light rays pass through a small opening and form an inverted image on the other side. The resulting image was barely perceptible on the light-drenched wall. But it struck Torralba that the world is suffused with visual information that our eyes fail to see.
“These images are hidden to us,” he said, “but they are all around us, all the time.”
The experience alerted him and his colleague, Bill Freeman, both professors at the Massachusetts Institute of Technology, to the ubiquity of “accidental cameras,” as they call them: windows, corners, houseplants and other common objects that create subtle images of their surroundings. These images, as much as 1,000 times dimmer than everything else, are typically invisible to the naked eye. “We figured out ways to pull out those images and make them visible,” Freeman explained.
The pair discovered just how much visual information is hiding in plain sight. In their first paper, Freeman and Torralba showed that the changing light on the wall of a room, filmed with nothing fancier than an iPhone, can be processed to reveal the scene outside the window. Last fall, they and their collaborators reported that they can spot someone moving on the other side of a corner by filming the ground near the corner. This summer, they demonstrated that they can film a houseplant and then reconstruct a three-dimensional image of the rest of the room from the disparate shadows cast by the plant’s leaves. Or they can turn the leaves into a “visual microphone,” magnifying their vibrations to listen to what’s being said.
www.quantamagazine.org
“These images are hidden to us,” he said, “but they are all around us, all the time.”
The experience alerted him and his colleague, Bill Freeman, both professors at the Massachusetts Institute of Technology, to the ubiquity of “accidental cameras,” as they call them: windows, corners, houseplants and other common objects that create subtle images of their surroundings. These images, as much as 1,000 times dimmer than everything else, are typically invisible to the naked eye. “We figured out ways to pull out those images and make them visible,” Freeman explained.
The pair discovered just how much visual information is hiding in plain sight. In their first paper, Freeman and Torralba showed that the changing light on the wall of a room, filmed with nothing fancier than an iPhone, can be processed to reveal the scene outside the window. Last fall, they and their collaborators reported that they can spot someone moving on the other side of a corner by filming the ground near the corner. This summer, they demonstrated that they can film a houseplant and then reconstruct a three-dimensional image of the rest of the room from the disparate shadows cast by the plant’s leaves. Or they can turn the leaves into a “visual microphone,” magnifying their vibrations to listen to what’s being said.
The New Science of Seeing Around Corners | Quanta Magazine
Computer vision researchers have uncovered a world of visual signals hiding in our midst, including subtle motions that betray what’s being said and faint images of what’s around a corner.
www.quantamagazine.org
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