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Daylight Balanaced cmos


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#1 Jed Shepherd

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Posted 01 October 2010 - 05:36 AM

I was recently talking to someone that was saying that the red performs best at daylight color temperature and that i should light accordingly even when indoors. Is this right?
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#2 Adrian Sierkowski

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Posted 01 October 2010 - 07:13 AM

Yes, RED is a bit better in Daylight than T, but the newer RED MX sensor takes care of any problems you should have. It's a question of testing, some people are quite alright with the noise the M sensor had in tungsten light.
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#3 K Borowski

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Posted 01 October 2010 - 10:18 AM

I would think that all CMOS/CCD chips are ideally balanced for either daylight or tungsten light and, as-such, every camera is natively cleaner at either a daylight, tungsten, or intermediate Kelvin temperature setting.

Don't some HD cameras actually use optical filters for color correction, or is that the viewfinder only that I'm thinking of?
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#4 Adrian Sierkowski

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Posted 01 October 2010 - 11:46 AM

I'm pretty sure all chips are D balances, around 5000K, and yes, some systems do have optical filters behind the lens on a filter wheel, but that's generally the higher end non-prosumer broadcast cameras.
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#5 K Borowski

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Posted 01 October 2010 - 01:11 PM

Thanks A. Makes sense since they probably have equal amounts of RGB sites, and tungsten would be disproportionately red light (so more blue and green sites needed natively).
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#6 Kieran Scannell

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Posted 01 October 2010 - 03:19 PM

Don't some HD cameras actually use optical filters for color correction, or is that the viewfinder only that I'm thinking of?


Karl are you being serious?
Because you do know that film camera's also use optical filters for colour correction right?
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#7 John Sprung

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Posted 01 October 2010 - 04:50 PM

Thanks A. Makes sense since they probably have equal amounts of RGB sites, and tungsten would be disproportionately red light (so more blue and green sites needed natively).


Actually it has to do with the native sensitivity -- or lack thereof -- of the silicon under the RGB filter mask. It's not as sensitive to blue as to the rest of the spectrum, so giving it more blue by going for a daylight-ish 5000 Kelvin yields more image photons and therefore a higher signal to noise ratio in the blue.

There are two widely used mask patterns. Bayer uses twice as many greens as red or blue (the four squares to the top left of this post), the Sony and Genesis use a stripe pattern with equal numbers of each.




-- J.S.
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#8 Keith Walters

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Posted 02 October 2010 - 05:39 PM

Actually it has to do with the native sensitivity -- or lack thereof -- of the silicon under the RGB filter mask. It's not as sensitive to blue as to the rest of the spectrum, so giving it more blue by going for a daylight-ish 5000 Kelvin yields more image photons and therefore a higher signal to noise ratio in the blue.

There are two widely used mask patterns. Bayer uses twice as many greens as red or blue (the four squares to the top left of this post), the Sony and Genesis use a stripe pattern with equal numbers of each.




-- J.S.

Strictly speaking, it's more to do with the fact that red light penetrates further into silicon than blue light, which is the basis of the colour separation system used in Foven sensors.

In the past the convention was to have cameras natively white balanced for tungsten, because camera tubes are more sensitive to blue and green than red. That worked out nicely, because tungsten lights are deficient in green and blue, and 3200K turned out to be pretty close to optimum white balance for Saticon tubes and the like. In daylight you usually had light to throw away, and so you could put on an orange filter to knock out some of the green and blue without introducing noise

With silicon sensors, the situation is reversed; the silicon sensors are more sensitive to blue than red, however for a while the convention was to retain a "native" white balance of 3200K, simply for compatibility with existing tube cameras.

The first generation of CCD broadcast cameras had to have peltier solid state coolers fitted to the blue CCDs (the things they have in compact 12V fridges), because the blue channels were so noisy in tungsten-lit studios!

The situation with single-chip sensors is more complex, because you can't individually adjust the ADC scaling for the red green and blue channels like you can with a 3-chip camera. If the scaling is set for full output from the red-filtered pixels, it's going to be way down for the blue.

With a 12-bit ADC, if the maximum red output is 4096 levels (ie 212), on 3200K balanced white, the blue-filtered pixels might only be putting out 512 (28levels or even less. One of the many drawbacks of single-sensor cameras, and one of the many reasons 3-chip designs are alive and well and even appearing in high-eng consumer cameras.

As far as the best white colour to use for the RED, surely the answer is whatever RED recommend!
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#9 John Sprung

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Posted 04 October 2010 - 12:55 PM

In the past the convention was to have cameras natively white balanced for tungsten, because camera tubes are more sensitive to blue and green than red. ....

With silicon sensors, the situation is reversed; the silicon sensors are more sensitive to blue than red, ...


Did you mean "red than blue" in that last sentence?





-- J.S.
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#10 Keith Walters

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Posted 04 October 2010 - 06:27 PM

Did you mean "red than blue" in that last sentence?
-- J.S.

More or less :rolleyes: \
It was actually supposed to be:
"the silicon sensors are less sensitive to blue than red"
but yours is an acceptable workaround :P
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#11 Mike Brennan

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Posted 05 January 2011 - 04:03 PM

The surprising development is that manufacturers of single chip cmos cameras do not demand the use of cc filters?
But once a photo site is saturated thats it and it makes sense, in theory, to at least roughly balance the optical path to match the sensor to avoid massive amounts of gain in one or two channels being added within camera or in post to rebalance the image.

Tests by end users tend to not explore this aspect, perhaps because it is a convenient truth not to have to use cc filters on location:)





Mike Brennan
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