How electronics sees color

[tw]

Foveon's X3 image technology will first appear this month in a new SA9 single lens reflex camera from Sigma Co of Tokyo. Sigma is the world's largest supplier of after-market 35 mm lenses. Other X3 based cameras may appear next year.

Foveon's chips are being manufactured by National Semiconductor. Of course, Eastman Kodak claims to have tried that approach 15 years ago on CCD devices. But then one can appreciate why Kodak is in financial trouble - too many good ideas quashed by MBA management who could not appreciate value until the product appears on a spread sheet.

The X3 also offers a lower signal to noise ratio meaning that electronic cameras can take pictures in lower light - strobe light not necessary. But metamerism is a weakness in its design. Each pixel does not sample red, green and blue consistently. Particularly difficult is yellow - a combination of red and green. The depth of each photodiode is believed critical in making accurate color reproduction. Getting every photodiode accurate in an array is statistical quality control problem. Blue would be detected at about 0.2 micrometers into silicon. Green at 0.6 um, and Red at 2 um.

Also believed to exist in the X3 chip are circuits that compensate based upon adjacent pixels. This interpolation occurs without a separate DSP processor.