New CMOS sensor delivers full color

Present CCD and CMOS image sensors detect only one color of the three required colors at each pixel and must therefore interpolate the remaining two undetected colors.

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Th 89197
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Present CCD and CMOS image sensors detect only one color of the three required colors at each pixel and must therefore interpolate the remaining two undetected colors. This drawback limits the range and accuracy of the acquired colors and introduces imaging errors. Now, a new image sensor holds the promise of overcoming existing restrictions and providing a breakthrough in full-color imaging.

Foveon Inc. (Santa Clara, CA; www.foveon.com) has unveiled two X3 CMOS image sensors that capture red, green, and blue light by stacking three photodetectors in silicon at every pixel location. The light of these three colors is absorbed at different depths in the silicon: blue light is absorbed near the surface, green light is absorbed farther down, and red light is absorbed even deeper.

As a result, Foveon technology delivers increased image sharpness, better color detail, and fewer color artifacts in comparison to other CCD and CMOS image sensors that contain just one layer of monochromatic photodetectors and one photodetector per pixel. Unlike other image sensors, X3 image sensors capture the full color of an image without using a color mosaic filter and without the expense, complexity, and limitations of multichip systems such as 3-CCD cameras. Moreover, these sensors incorporate proprietary Variable Pixel Size technology, which can change pixel sizes from small to large instantly.

The Foveon X3 image sensors are in production using standard 0.18-µm CMOS semiconductor technology at National Semiconductor 's South Portland, ME, manufacturing facility. Available immediately, the F7-35X3-A25B image sensor offers a 2304 X 1536 X 3 pixel array, provides 10.3 million total effective photodetectors, and measures 20.7 X 13.8 mm (25 mm diagonal) with an image area of 20.7 X 13.8 mm. Frame rate is 2 frames/s for the full array and 30 frames/s for a 640 X 480-pixel resolution. The second image sensor, the F10-14X3-D08A, offers a 0.5-in. optical format, measures 6.4 X 4.8 mm, and provides a 1344 X 1024 X 3-pixel array. It will be available in sample quantities at the end of 2002.

Foveon officials say that the company does not plan on developing its own cameras. Instead, it is offering product opportunities to camera OEMs by offering design kits consisting of a hardware reference platform and development software.

Because the X3 technology is also scalable, it is expected to drive a new generation of digital-color-camera designs. These cameras are envisioned to eliminate color errors, improve image quality, boost performance, and lower manufacturers' costs—attibutes the vision/imaging industry needs to spur market growth.

George Kotelly
Editor in Chief
georgek@pennwell.com

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