3D Underwater Images Made Possible by Flickering Sunbeams
By taking advantage of a previously undesirable optical effect, researchers from the Technion-Israel Institute of Technology and the University of Miami have discovered a way to reconstruct the three-dimensional structure of underwater scenes.
When beams of sunlight enter water, they move rapidly and change the illumination of submerged objects, creating bright lighting "hot spots," as well as dimmer areas on the surfaces of objects. In an effect called “underwater flicker,” the wavy water surface changes the beam direction and focuses light in a way that changes rapidly with the wave motion. Historically, flicker has been considered an undesirable effect that confuses and degrades image quality.
But instead of trying to eliminate flicker, the team led by Prof. Yoav Schechner of the Technion Faculty of Electrical Engineering used the natural rapid and random motion of the light beams and illumination hot spots to identify a unique signature for each point in the scene. By doing so, they were able to easily gauge the distance to each point, resulting in improved picture quality and photographs with three-dimensional depth.
The technique solves a difficult problem in robotic stereoscopic vision, wherein a computer tries to match image points seen by two video cameras to gauge the distance to each 3D structure. This matching is especially complex in regions lacking distinctive texture (such as walls, sand or uniform surfaces), which lack points to “lock on," match unambiguously, and find the distance to. But underwater, the Technion researchers say, this problem can be solved simply and reliably.
“We’ve found a solution to a longstanding problem by using a natural and spontaneous phenomenon,” says Prof. Schechner. “As time passes, underwater flicker creates a unique signature for each point in the scene, regardless of its texture, in the two video cameras. This reliable and dense correspondence allows us to reliably derive the 3D structure of the scene.”
In the future, the method could be utilized for a myriad of applications including underwater mapping; marine archeology; oceanic engineering; inspection of underwater structures (bridge and port foundations, tubes, and cables), search, rescue and recovery; and recreational photography.
The 3D recovery method was validated in several scuba diving experiments in the Mediterranean. It was presented at the prestigious IEEE* International Conference on Computer Vision (Japan, 2009). The research was supported by the US-Israel Binational Science Foundation (BSF).
Also contributing to this research were Technion graduate student Yohay Swirski, Technion graduate Ben Herzberg, and Shahriar Negahdaripour from the University of Miami.
In 2004, Prof. Schechner and then-graduate student Nir Karpel devised a method for improving the quality of flicker-prone underwater images so that it appears they were photographed under stable conditions.
The Technion-Israel Institute of
Technology is Israel's leading science and technology university. Home to the country's winners of the
Nobel Prize in science, it commands a worldwide reputation for its pioneering
work in nanotechnology, computer science, biotechnology, water-resource
management, materials engineering, aerospace and medicine. The majority of the founders and
managers of Israel's high-tech companies are alumni. Based in New York City,
the American Technion Society (ATS) is the leading American organization
supporting higher education in Israel, with offices around the country.
(* Institute of Electrical & Electronics Engineers)