Clearing Up Underwater Photos

When the visibility is 100 feet, it can still seem like there’s a thin layer of fog out there. Backscatter, as it’s called, is caused by ambient light from above the water’s surface, scattering into the line of sight. For photographers, what can be otherwise stunning shots show up in a haze. And, that’s why telescopic lenses don’t work underwater: they enlarge and enhance both backscatter and the subject.

Scientists from the Technion-Israel Institute of Technology in Israel have discovered a solution, says Dr. Yoav Schechner. They have developed an algorithm that applied through computer software to photos shot with a polarizing filter, eliminates the backscatter. “Our hunch was that if you take underwater photos with this filter and use a mathematical analysis of physical things that occur in water, you can undo these distortions and compensate for them,” he says. Unlike standard photo imaging programs that treat a photographic image as a whole, the new method corrects different elements such as objects that are closer or distant individually, according to need.

According to the researchers, the method not only makes it possible to see objects that previously appeared blurry and out of focus, but also makes it possible to estimate distances underwater and give the photos three-dimensional depth. It will be a boon for marine biologists, Schechner said, because photographers wouldn’t have to disturb animals with close-ups.

Schechner says the program could be placed on a chip embedded within the camera or be integrated with existing video systems to improve underwater video quality vastly. The researchers are negotiating commercialization of the program.

From a report on the Institute of Electrical & Electronics Engineers (IEEE) Conference on Computer Vision and Pattern Recognition in Washington, D.C. June 2004. Published by www.globes.co.il. September 02, 2004. For more information, visit Dr. Schechner’s website at www.ee.technion.ac.il/~yoav