Saturday, August 14, 2010

Can We improve on the Digital Color Camera?

During the early days of color television when people still had B&W televisions both signals had to be transmitted so a quadrature modulation system was used to send monochrome, M, and two differences I and M. The monochrome channel was the luminance Y and a transformation from RGB to Y was done using the following equation but the assumption was the use of illuminant C which is north sky daylight.

(The quadrature system is also used for stereo.) So the luminance is definitely dependent on the wavelengths of the light illuminating a scene.

One wonders if it is possible to improve on the color camera. Digital color cameras use either the 3CDD method or Bayer filters to capture the RGB information. But there are other color spaces such as CMYK. A variant on CMYK might be RGBY in which an unfiltered image is used instead of a second G image. A camera using RGBY would be able to take B&W pictures. One of the reasons for using M/I/Q in color television was the reduction in bandwidth needed to store an image. Something similar might improve image compression for storage. An opponent color space is also a possibility.

I still have some doubts about the heights of the peaks on the camera spectrometer. I assumed an equal energy white for the illuminant which has equal amounts of R, G and B and so each coefficient of the Y conversion formula is then 1/3. Daylight illumination is close to this. The light from the fluorescent bulb is whiter than normal. So the assumption of an illuminant affects the conversion process. And the old formulas will no longer work if new primaries are being used.

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