Computer vision algorithm removes the water from underwater images
Underwater photography is hard to get right. Special filters, artificial lights, and top-of-the-line underwater cameras can help, but there’s still a lot of water between the camera and the object in the photo. We’ve become accustomed to the blue-green tint of underwater photography.
How would the ocean look without water? What are the true colors of a coral reef? Thanks to a new computer vision algorithm called Sea-thru, we can see what an underwater scene would look like if it was photographed through the air instead of water.
Sea-thru removes the visual distortion that occurs as light travels through the water to produce a color-accurate image. Sea-thru was developed by Dr. Derya Akkaynak, and engineer and oceanographer, and Dr. Tali Treibitz, an electrical engineer. And the results are not only stunning but also a physically accurate correction.
According to Scientific American, “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 algorithm effectively reverses image distortion from water pixel by pixel, restoring lost colors.”
Akkaynak developed Sea-thru as a post-doctoral fellow at the Marine Imaging Lab, run by Dr. Tali Treibitz, at the University of Haifa. Sea-thru is licensed to SeaErra Ltd.
The reason for the blue-green tint in underwater photos is the way light travels through deep water, where blue and violet wavelengths are absorbed least compared to the other wavelengths. The more water the light travels through, the less red, yellow, and orange wavelengths reach the object. In coastal waters, the blue and green light is absorbed faster, leaving more red light and causing the dominant brown hue.
There’s also an issue of small particles in the water, which create backscatter or haze. The further the photographer is from the object in the photo, the hazier the object becomes, much like looking at an object through a light fog.
Sea-thru works on raw images or videos taken with natural lighting, removing the need for expensive and difficult to set-up artificial underwater lighting. It also helps in reconstructing images of objects that are further away from the light source, where the underwater strobes don’t reach.
The computer vision algorithm is a physics-based color reconstruction algorithm designed for underwater RGB-D images, where D stands for the distancefrom the camera to the object. The Sea-thru algorithm requires the distance between each pixel in the scene from the camera, as almost all parameters governing loss of colors and contrast depend on distance in some non-linear way.
