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Researchers at MIT Media Lab have demonstrated a method of exploiting light polarisation – the phenomenon behind the polarised glasses used for 3D films – to increase the resolution of 3D imaging by as much as 1,000 times.
The method could enable high quality 3D cameras being built in to mobile phone, as well as quickly scanning an object to produce a 3D printed replica.
“Today, they can miniaturize 3-D cameras to fit on cellphones,” said one of the researchers, PhD student Achuta Kadambi. “But they make compromises to the 3-D sensing, leading to very coarse recovery of geometry. That’s a natural application for polarization, because you can still use a low-quality sensor, and adding a polarizing filter gives you something that’s better than many machine-shop laser scanners.”
Polarisation not only affects the way in which light reflects from physical objects, the polarisation of light carries useful information about the geometry of the objects themselves. To extract this useful information, the researchers employed a the Graphics Processing Unit of a Microsoft Kinect.
With a regular polarising lens placed in front of the Kinect camera, the researchers took three photos of the object, rotating the lens each time. The algorithm then extracted the depth of field information from the Kinect system, and compared light intensities in each of the photos. When the researchers added their system, the Kinect, which can already resolve features as small as a centimetre across from a distance of several metres, was able to resolve features the size of tens of micrometres – a thousandth of the size.
The new system could also have benefits for self-driving cars. While their onboard systems are great in clear weather, fog or rain can seriously interfere with their visual algorithms. This is due the water particles in the air scattering light in unpredictable ways.
In several simple tests, the researchers showed that their system can use information contained in interfering wave patterns to handle scattering. “Mitigating scattering in controlled scenes is a small step,” Kadambi says. “But that’s something that I think will be a cool open problem.”