Electronic Design

Embedded Algorithms Enable Low-Cost Cell-Phone Zooming

Digital cameras, by themselves and in cell phones, represent one of the hottest segments of the consumer market. To compete, designers need to lower their costs while improving performance. Tessera Israel achieves these goals as well as better reliability with software algorithms that eliminate the need for conventional mechanical zooming.

The company’s OptiML Zoom uses optical distortion to zoom in on an image with up to 3X magnification. This solution also provides more image light and a greater depth of field. And, its unique lens design costs about as much as a regular camera lens to manufacture, according to Tessera.

“The only additional cost, which is minor, is embedding our algorithms in the camera’s image pipeline that already exists,” explains Evan Kali, vice president of marketing for Tessera’s Smart Optics Division.

Two versions of the OptiML Zoom capability are available. Designed for low-value zoom applications, the first is based on a fixed-focus lens distortion that provides variable magnification across the image sensor, high magnification at the image sensor, and low magnification at the image border. The second involves a dual-state assembly and a lens with distortion to provide high-value zooming. In both cases, digital restoration corrects the distortion of the captured image.

“Think of our approach by looking at a typical fisheye lens in which the sharpest image is at the center of the lens and the periphery portions of the view are not as sharp,” Kali says. “What we do is over-sample the image information in the periphery to increase resolution in the center, and we achieve this with a significant performance advantage compared to the most advanced digital zooming techniques in use today.”

“We believe that the OptiML Zoom solution meets the growing demand for better functionality in camera phones, providing an optimal combination of price, performance, size, and ease of integration,” says Michael Berezuik, Tessera’s chief operating officer.

POINT SPREAD FUNCTION
OptiML Zoom accomplishes optical zooming without any moving parts via controlled distortion of the image in an optical system that matches the point spread function (PSF) to the pixel size over the whole sensor area, exploiting the interaction between the PSF of an optical system and the quantized resolution of a solid-state imager. The PSF describes the response of an imaging system to a point source or point object

The solution is based on unique fixed-focus optics that provide magnification in the center of an image’s field of view with respect to the image’s borders. The distorted image is magnified in the center and compressed near its borders. The central region of the image occupies more of the sensor area, while the image borders occupy less, compared to a standard imaging system (see the figure).

The controlled distortion ensures that the PSF becomes smaller in the border area, compared to the PSF provided by a standard lens module. Consequently, the PSF is spread over a smaller number of sensor pixels. If the PSF is designed to have a region of support of a single pixel, no image information is lost.

Consider the center of a viewed object’s field of view, where the image is magnified to the point where the resulting PSF size is also about one pixel. Once again, no loss of information occurs, since the sensor pixel size has dictated the image resolution in this region from the beginning.

Therefore, the optical distortion can be seen as a magnification mapping of the PSF size to match the pixel size in the whole field-of-view region. This condition is optimal since no information loss occurs due to under-sampling and no detail is lost through oversampling. Essentially, the information that’s contained in the captured image is maximal.

DIGITAL CORRECTION

Available for licensing, OptiML Zoom is part of Tessera’s portfolio of imageenhancement solutions. The company already has announced its OptiML ultra-fast lens (UFL) capability (see “Unique Technology Boosts Image Quality Of Low-Cost Cameras,” Electronic Design, April 24, 2008, ED Online 18607).

TESSERA INC. www.tessera.com

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