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kottke.org posts about Erik Olsen

This Algorithm “Removes the Water from Underwater Images”

posted by Jason Kottke   Nov 25, 2019

As detailed in this Scientific American article by Erik Olsen, engineer and oceanographer Derya Akkaynak has devised an algorithm that “removes the water from underwater images” so that photos taken underwater have the color and clarity of photos taken in air. She calls the algorithm “Sea-thru”.

Sea-thru’s image analysis factors in the physics of light absorption and scattering in the atmosphere, compared with that in the ocean, where the particles that light interacts with are much larger. Then the program effectively reverses image distortion from water pixel by pixel, restoring lost colors.

One caveat is that the process requires distance information to work. Akkaynak takes numerous photographs of the same scene from various angles, which Sea-thru uses to estimate the distance between the camera and objects in the scene — and, in turn, the water’s light-attenuating impact. Luckily, many scientists already capture distance information in image data sets by using a process called photogrammetry, and Akkaynak says the program will readily work on those photographs.

The paper says the process “recovers color” and in the video above, Akkaynak notes that “it’s a physically accurate correction rather that a visually pleasing modification” that would be done manually in a program like Photoshop.