Does any1 know what it would take to improve Foveon high ISO performance?

Started Aug 31, 2012 | Discussions thread
Aku Ankka
Aku Ankka Contributing Member • Posts: 591
Re: One main question

xpatUSA wrote:

Aku Ankka wrote:

xpatUSA wrote:

Of course, Foveon cheats by somehow adding the R, G and B quantum efficiencies together and calling it "total quantum efficiency" (the black line above). 70%? . . . don't be fooled.

This is not cheating. It is what the QE for each pixel is. The individual layers each get a part of it which the curve is also shown for completeness.

( my bold )

Not so, Aku.

Actually it is so.

The property "quantum efficiency" is only used to describe the light-collecting ability of a single photo-diode

No. In practise it tends to be the case, but QE reports simply what percentage of photons are turned into carriers. If you have stacked photodiode system (with photodiodes interconncted - they're not separate) you can get figurs for all the readout points as well as the totall (which is - surprise surprise - the sum of all the three readouts).

  • whether it stands alone, or is one member of a pixel group of three as found in our beloved sensor. So you can't say "QE for each pixel ". Well, you could but it wouldn't be right.

Sure it is. You're creating an artificial limitation.

What Foveon says is like adding up the QE's of the four photo-diodes in a Bayer grouping and probably getting more that 100%, CFA included or not

No, it's very different. The Foveon photodiode combination shares the same spatial position.

Please imagine the Foveon sensor created a greyscale image, ie. it only had one photodetector per pixel - that would be no different from what is is now, except that the pixel also gets (poor) color information. What percentage of the photons the sensor uses does not change simply because more information is extracted out of them.

. And Foveon's phrase " total quantum efficiency" is just plain misleading B-S, deliberately so, IMHO. Good though, even the University of Arizona fell for it!

No it is not. It is perfectly normal.

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