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No Bayer Pattern CMOS systems


Tyler Purcell

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Foveon sensors are not that great. One of my first 'real' stills camera's had a Foveon sensor in it. I believe it was a Fujifilm digital camera but I don't recall now - it's been probably 10 years. Colors were okay, but even back then I noticed the sensor had problems resolving red - often tinting it toward magenta. The sensors were also not very capable of large output - as would be needed to sample a sensor 24 times a second, let alone the 60+ people expect now-a-days. I don't know what improvements have been made by Foveon since then, but I have not seen their sensors used in more than just a few specialty cameras. Until you mentioned it, I didn't even know they still existed - but apparently they do.

 

Could be a cost issue, reading-speed issue, color issue, or any number of things. Mainly, I think it's that CMOS bayering on a single chip has worked so well that camera makers see little need to invest millions of dollars in R&D for a different option. Let's face it, an appropriately sized CMOS bayer sensor with the correct compression and bit depth produces images that are fantastic and need little improvement.

The one thing about bayered sensors that always puzzled me though is this: Why do they add almost double the green photosites compared to the others? It seems they would get better color reproduction by giving an equal number of sites to each color. Preferably, each final pixel rendered would have 4 total photosites (R, G, B, L). This would of course mean you'd need a 8MP sensor to get 2MP of final render, but given that many sensors now have 20+ MP, I don't see the issue. Why now group 4 pixels into one final pixel rather than using line-skipping?

Edited by Landon D. Parks
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Peltier elements are already used in some modern digital cinema cameras to assist cooling the sensor. If I remember correctly at least blackmagic and arri are using it.

 

Btw nowadays when we live again the anamorphic/large sensor part of the periodical 3D image format cycle, people most likely take bigger single sensor camera over the 3chip one when the optics is concerned. With bigger sensor you also need more ffd and possibly special lenses but you get more "wow factor" with todays audiences compared to a 3ccd great color response camera. Most of the asudience wants the films specs to look good on paper too, not only on screen

Actually the first Sony SP betacams that came out in 1989 had Peltier coolers on the blue CCD. They were also used in high-end video surveillance cameras.

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The one thing about bayered sensors that always puzzled me though is this: Why do they add almost double the green photosites compared to the others? It seems they would get better color reproduction by giving an equal number of sites to each color. Preferably, each final pixel rendered would have 4 total photosites (R, G, B, L). This would of course mean you'd need a 8MP sensor to get 2MP of final render, but given that many sensors now have 20+ MP, I don't see the issue. Why now group 4 pixels into one final pixel rather than using line-skipping?

 

They use much more green because that's how the human brain perceives the visible spectrum. We basically see a bit of red on one end and a bit of blue on the other with a huge mass of green in the middle. When we rose from the primordial ooze we were surrounded by a whole lotta green and that's pretty much stuck with us. This is why the basic color adjustments work the way they do: color temperature is essentially adjusting the relative strength of red v. blue, and tint control is plus/minus on the green strength (green/magenta balance).

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