Single-pixel imaging compresses information

Researchers at Rice University (Houston, TX, USA; www.rice.edu) have combined a MEMS array with a single optical sensor to create an image/video camera that incorporates compressed sensing. "White noise is the key," says Richard Baraniuk, the Victor E. Cameron professor of electrical and computer engineering at Rice. "Thanks to some deep new mathematics, we're able to get a useful, coherent image out of the randomly scattered measurements."

The prototype camera uses a digital micromirror device (DMD) from Texas Instruments (Dallas, TX, USA; www.ti.com) and a single photodiode. The object of interest is focused upon the DMD, which has a pseudorandom pattern mapped onto it. The micromirrors can tilt by ±12º about the plane of the chip-the white parts of the pattern indicate mirrors tilted by +12º and the black ones are tilted by -12º. The reflected light from the white/black areas of the pattern is collected on a photodiode. Every pseudorandom pattern gives one coefficient (photovoltage), and, using these coefficients and the random seed, an image can be reconstructed.

Baraniuk says, "The beauty of compressed sensing lies in the fact that we measure (sample) the image/video fewer times than the number of actual pixels. This can significantly reduce the computation required for image/video acquisition and encoding." It currently takes about five minutes to take a picture with the prototype camera, and only stationary objects have been photographed. Initial efforts are aimed at developing the camera for scientific applications where digital photography is unavailable, such as terahertz imaging, although imaging for the consumer market may be possible.