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Old December 17th, 2003, 05:13 AM   #16
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Re: Why not 3-ccd for ex. latitude?

<<<-Why not have a 3-CCD block with three color chips, recording the shadow, mid range and highlights (that is, for example, the two chips recoding 2 or three stops above and below normal) to create a sort of bracketing system, which is combined into one image? -->>>

There are probably several reasons, and not just cost, although cost is the big killer. One is the problem of calibrating the different sensors to one another, so that ignoring the quantization issue, they all measure the same for a common input which does not saturate the two sensors being compared. The second must have to do with flaring by the lenses or prisms, and the diffusive nature of light. Unlike a film scanner, which uses a controlled beam of light, the light coming into your camera lens is anything but controlled and spot accurate. This straddling issue must vex the logic which decides how to combine the outputs of multiple sensors of different resolutions. It takes a lot of dsp power, even in existing products which do pixel re-sampling, i.e., your typical consumer and prosumer cameras of either video or still categories. End result in either case: a fuzzier picture because you have to hedge your bets in compositing the output.

This seems to be an idea which has already been patented or disclosed, and either proved to be impractical, or prone to anamolies. I'll give you an example from the audio domain. Suppose you want to build a high res, high sampling rate A/D converter. Why not combine two inexpensive 16-bit 1 MHz sampling A/D's to get an 18-bit or 20-bit 1 MHz converter? Because of the cross mononiticity issue and extraordinary difficulty in ensuring the two converters track each other. In the FFT domain, this leads to distortion and non-linear spurs.

The final reason must have to do with being a purist. Engineers would rather wait for technology to catch up (and produce a sensor with a high dynamic range) than settle for an ad hoc approach using multiple sensors. The only time you use the combinative approach is when you exhaust the non-combinative approaches, as in full range vs. multi-driver speaker technology. (Electrostatics still can't achieve deep bass).
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Old December 26th, 2003, 06:18 PM   #17
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This could be done with 2 CCDs easier than with 3 CCDs. Yes, it is a good idea and not a new idea, but I am happy with my Canon EOS 10D, and if a video camera could capture that quality but at a lower res I would be happy. I would expect Canon to lead the pack with this since they are doing so well with digital SLRs.

This has also been done with a single CCD and 1/2 the frame rate but changing the gain of the chip every other frame. It is uses by security cameras.

If you go to a video trade show you see tons of this stuff.

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