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Technion engineer clears up underwater photos

Posted on 04.05.2004 - 14:57 EDT in SCIENCE & TECH NEWS by Rons_ROV_Links

A carefully constructed algorithm and a commonplace camera filter can not only dramatically improve the quality of underwater photography, but may someday save lives as well.

The technique developed over the past 18 months by scientists from the Technion-Israel Institute of Technology have started as a means of improving underwater photography. But it has wide applications in engineering, science, and even lifesaving, and has aroused much interest around the world – even before Dr. Yoav Schechner is due to present the work before the prestigious IEEE Conference on Computer Vision and Pattern Recognition in Washington, DC, in July.

Schechner, of the Technion's electrical engineering faculty, first intended to tackle a problem he encountered as an amateur diver.

"My professional field is optics and using computer vision to solve optical effects that cause visibility degradation. I have dived from time to time in the Gulf of Eilat and off Australia, and was curious about dealing with the problem of taking photos underwater," he told The Jerusalem Post.

"Even in the cleanest water, you have poor visibility. There are many reasons for it. We analyzed the physical factors.

"The main problem," said Schechner, "is the ambient light from the surroundings; it undergoes scattering into the line of sight which is called backscatter. We and others understood that if the backscatter can be neutralized, the photo image would be much better."

Schechner and master's degree student Nir Karpel read "about 100 articles and books in the field" after developing their hypothesis about using an algorithm and attaching a simple polarizing filter – which costs less than $100 and is widely used for conventional (overland) photography. Marine animals also use polarization for improved vision underwater.

"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. At first we had no equipment and had no real experience in this, so we took some scientific risk when we developed our hypothesis. No one in the world had previously used this mathematical approach," Schechner added.

When they did get equipment and dived with it, they "saw the algorithms didn't work so well, so we fine-tuned them until they did."

Their method, to be outlined in an article that will be published in the IEEE conference's official proceedings, 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 would be a boon for marine biologists, Schechner said, because photographers wouldn't have to disturb animals with closeups. The technique could also help lifesavers better see into swimming pools to prevent drowning and might even be applied to improve photography in living tissue.

It technique can be used for checking and monitoring underwater pipes and cables, bridge pylons, drilling rigs, the infrastructure of artificial islands, archeological sites, robots working in water, sailing vessels, and atomic reactors. It also could be of great assistance in scientific research (biology, underwater archeology, and underwater mapping) – and, of course, for amateur underwater photographers.

03 May 2004
Jerusalem Post
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