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One of the challenges facing camera-phone and webcam makers, as well as designers of other small-size, low-cost mobile cameras, is image quality. These products don’t target the professional photographer, yet their users now expect better results. The easiest approach is to integrate a better camera in the device, which in turn raises the overall cost.

Tessera Inc. offers one solution: the OptiML ultra-fast lens (UFL). This unique image-enhancement technology promises significantly higher-quality images in smaller form factors at lower costs. The OptiML UFL combines an advanced lens design with embedded processing technology in the form of an algorithm to improve the low-light performance of the camera.

Essentially, it increases the amount of available light by as much as 250% without degrading field depth or other imaging parameters. In addition to notably higher-quality images, the technology functions without the need for any mechanical parts, which lead to larger, slower, more expensive, and less reliable end products.

PROPRIETARY LENS DESIGN
The unique OptiML UFL lens design addresses the problems associated with the ever-decreasing pixel size exhibited by the current range of smaller silicon imaging devices. This decrease in pixel dimensions leads to a reduction in the amount of light each pixel can handle, which in turn degrades image quality.

Compared to a standard, fixed-focus lens common to camera phones, the OptiML UFL lens design enables a substantial decrease in the F/# (lens aperture size). For example, a standard fixed-focus lens provides a typical aperture size of f/2.8, while the Tessera lens can achieve an F/# as low as f/1.75.

Naturally, this reduction level depends on system characteristics like pixel size, lens-module height, and the number of plastic elements (three or four). It also depends on any manufacturing constraints on the overall design.

The first benefit of the lens design is vast improvements in image quality when taking photos indoors and other environments where low-light conditions are the norm (see the figure). Additionally, the technology has no negative impact on the camera’s close-range focus capabilities.

ALGORITHMS PROVIDE FURTHER ENHANCEMENTS
Compact OptiML algorithms support the ultra-fast lens design, operating as a standalone block in the instruction set processor pipeline. The algorithms provide additional signal processing to compensate for any loss of contrast while reducing noise in the output image. They also preserve edges, fine details, and texture.

In application, the algorithms enable an increase in spatial frequency response values for imaging both distant and close-up objects. They boost the signal-to-noise ratio gain in the realm of 6 dB as well. In terms of size considerations, the OptiML algorithms require approximately 100k gates, allowing for a single-chip topology in which the algorithms integrate as a part of the sensor.

Gartner researchers expect the market for camera modules in handsets to grow beyond 80% by 2010. Meanwhile, “improved low-light performance with no flash is one of the two most requested features for handsets,” says Tessera CEO Michael Bereziuk. If both statements hold true, Tessera will be on the right track to accommodate the surge.

Though the OptiML UFL targets compact, low-cost consumer products, it should find use in other imaging markets. As the technology is proprietary, Tessera is quite tight-lipped about its other target markets as well as any in-depth technical descriptions of the lens design and associated algorithms. The OptiML UFL is currently available for licensing.

TESSERA INC.
www.tessera.com/technologies/products/smart_optics/ufl.htm