A group of computer vision researchers from the US, Canada, and Europe have developed a technique to see around corners. It's the first time researchers have been able to capture shapes of curved objects using non-line-of-sight (NLOS) imaging techniques.
The technique relies on special light sources and sensors. What we see in day-to-day life is light reflecting off objects. Like the human eye, typical cameras detect this light.
But NLOS research is based on the fact that light reflects off objects in other directions, as well. A tiny amount of scattered light may in fact reach the eye after deflecting off walls or other objects but is washed out by brighter light sources.
NLOS imaging detects that light and attempts to extract useful information, including reconstructing the sides of objects that are normally out of view. The researchers so far have reconstructed the relief of George Washington's profile on a U. quarter.
"It is exciting to see the quality of reconstructions of hidden objects get closer to the scans we're used to seeing for objects that are in the line of sight," said Srinivasa Narasimhan, a professor in the Carnegie Mellon University Robotics Institute. "Thus far, we can achieve this level of detail for only relatively small areas, but this capability will complement other NLOS techniques."
The research is being conducted with the support of the Defense Advanced Research Project Agency's REVEAL program. Participating researchers are from Carnegie Mellon University, the University of Toronto and University College London. They're part of a larger NLOS collaborative team including scientists from Stanford University, the University of Wisconsin Madison, the University of Zaragosa, Politecnico di Milano and the French-German Research Institute of Saint-Louis.
"Other NLOS researchers have already demonstrated NLOS imaging systems that can understand room-size scenes, or even extract information using only naturally occurring light," Ioannis Gkioulekas, an assistant professor in the Robotics Institute, explains. "We're doing something that's complementary to those approaches -- enabling NLOS systems to capture fine detail over a small area."
The technique involved the use of an ultrafast laser to bounce light off a wall to illuminate an obscured object. Researchers used a lidar capable of detecting small amounts of light. By knowing when the laser fired pulses of light, the researchers could calculate the time the light took to reflect off the object, bounce off the wall on its return trip and reach a sensor, thereby enabling them to reconstruct an image of the side of the trip.
"This time-of-flight technique is similar to that of the lidars often used by self-driving cars to build a 3D map of the car's surroundings," said Shumian Xin, a Ph.D. student in robotics.
Applications include seismic imaging and acoustic and ultrasound imaging. The support of DARPA, the military's funding arm, also suggests military applications, potentially including non-line-of-sight targeting applications.
In addition to DARPA, the research is supported by the National Science Foundation, the Office of Naval Research, and the Natural Sciences and Engineering Research Council of Canada.