April 28, 2006
Written by Tommy Peterson–Geek’s Garden
Imaging chips revolutionized the photography industry, and now the chips themselves are being revolutionized by researchers at the University of Rochester.
A pair of recently patented technologies may soon enable power-hungry imaging chips to use just a fraction of the energy they use today and capture better images to boot — all while enabling cameras to shrink to the size of a shirt button and run for years on a single battery.
The University of Rochester team of Mark Bocko, professor of electrical and computer engineering, and Zeljko Ignjatovic, assistant professor of electrical and computer engineering, has designed a prototype chip that can digitize an image at the level of individual pixels. The researchers are now working to incorporate a second technology that will compress the image with far fewer computations than the best current compression techniques.
“These two technologies may work together or separately to greatly reduce the energy cost of capturing a digital image,” says Bocko. “One is evolutionary in that it pushes current technology further. The second may prove to be revolutionary, because it’s an entirely new way of thinking about capturing an image in the first place.”
The first technology being developed integrates an oversampling “sigma-delta” analog-to-digital converter at each pixel location in a CMOS sensor. Previous attempts to do this on-pixel conversion have required far too many transistors, leaving too little area to collect light. The new designs use as few as three transistors per pixel, reserving nearly half of the pixel area for light collection. Initial tests on the chip show that at video rates of 30 frames per second, it uses just 0.88 nanowatts per pixel — 50 times less than the industry’s previous best. It also trounces conventional chips in dynamic range, which is the difference between the dimmest and brightest light that can be recorded. Existing sensors can record light 1,000 times brighter than their dimmest detectable light, a dynamic range of 1:1,000, while the Rochester technology already demonstrates a dynamic range of 1:100,000.
The second technology has taken many researchers by surprise. Using a method called focal-plane image compression, Bocko and Ignjatovic have figured out a way to arrange photodiodes on an imaging chip so that compressing an image demands as little as 1% of the computing power usually needed.
Read the DPReview article from December, 2005.