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.
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