How electronics sees color

[tw]

Video detection involves breaking a picture up into little dots called pixels. A detector increases its voltage as the light intensity increases. Simple if this is a black and white picture. One detector per dot.

A pixel that displays color requires detection of three separate colors: typically red green and blue. Each pixel requires a detector for each color - that can output a separate signal for each color. It means each pixel must be focused so that diffferent colors strike each pixel. In simple terms, each pixel must have its own separate color filter. This means millions of pixels with three separate focused detectors for each color. It is rather a kludge where actually 50% are dedicated to green, 25% to red, and 25% to blue.

But the kludge is not done. Real color intensity is not fully known meaning that a processor must interpolate to convert color to reflect reality. Yes, that camera must perform complex picture modifications which is why moving picture cameras require so much more computer power - higher costs. Even worse, shiny object may fool the interpolation into creating coloured speckles, or artefacts where the image is brightest.

Foveon of Santa Clara, California has created the X3 sensor that captures red, blue and green light in one senor. The depth of each color's penetration into the semiconductor determines the detected color. The solution eliminates five problems. First the much less expensive sensor array does not require complex color filtering. Second, the array itself involves less sensors meaning smaller sensors, or more detailed pictures. Third, no interpolating and the many distortions created by that approximation including artefacts. Fourth, less power consumption since the interpolation need not be performed. Fifth, pictures can now be available real time - without wainting for the camera computer to process each picture.

Expect Foveon and X3 to be marked to all camera products as Dolby was marketed to audio equipment.

There are so many other interesting fundamental optics devices such as a semiconductor that than measure the light wavelength (color) by a voltage measurement. Or lasers that can actually change color (frequency) meaning simplifying the transmission of many different colors (data channels) on a fiber optic. Of course most of this will never be seen by the 'man in the street'. But Foveon's X3 promises fundamental change (innovation) in retail and commerical video products.

[jaguar]

wow thats really cool!! Any more details on how it works?
by the name is far too close to the forever accursed X10...

[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.

[tw]

The Sigma Designs X-3 based camera is now pictured (about page 20) in June 2002 issue of Popular Science.