Whenever light scatters off a surface, it forms an expanding sphere of photons, and this sphere traces out a cone as it extends through time. O’Toole (who has since moved from Stanford to Carnegie Mellon University) translated the physics of light cones — developed by Albert Einstein’s teacher, Hermann Minkowski, in the early 20th century — into a concise expression relating photon times-of-flight to the locations of scattering surfaces. He dubbed this translation the “light-cone transform.”

Self-driving cars already have LIDAR systems for direct imaging and could conceivably someday also be equipped with SPADs for seeing around corners. “In the near future these [laser-SPAD] sensors will be available in a format that could be handheld,” predicted Andreas Velten, the first author of Raskar’s seminal 2012 paper, who now runs an active-imaging group at the University of Wisconsin, Madison.
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