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Polorization lighting the shadows
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Written by Gizmo   
Saturday, 30 December 2006 09:39

For machine vision, separating shadows from actual objects has proven to be a very difficult problem to tackle, and this has been on of the factors limiting the ability of machines to interact with their environment.  While machines can typically handle single shadows on an object, when multiple shadows overlap on an object, the machines are unable to cope and become confused about the size and shape of the object being shadowed.

It seems researchers at the University of  Pennsylvania in Philadelphia have come up with a way to overcome this problem, by using polarized light .  Using an Olympus camera with a 4 megapixel resolution and 10-bit color depth, the researchers were able to retrieve the raw sensor data from the camera.  By placing a polarizing filter in front of the camera and then taking images of the scene at 0, 45, and 90 degrees of polarization, they were able to demonstrate that varying degrees of polarization could be used to improve the scene clarity.

Most light that is reflected from a flat surface becomes polarized to some degree, and since much of what we see is via reflected light, the technique holds promise for allowing machines to better distinguish objects from shadows.  The researchers have demonstrated near-real-time extraction of polarization data from images, and are working on methods of automating the filtering, such as using a liquid crystal polarizer sheet.

Image
(Images courtesy of Phtonics.com)Left: Normal image - Right: Polarized image

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