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Old December 16th, 2004, 05:11 PM   #1
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Dark Current Noise

Hi everyone,

I'm just curious if prosumer cameras actually remove the dark current noise from the CCD before recording to tape. I'd like to know so I can be prepared for it if it happens.

I'm not sure if this would matter much at the exposure lengths used with video though.

Anyone have any information about this?
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Old December 19th, 2004, 01:39 PM   #2
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I dont think they do. Leakage strongly depends on temperature, one needs to measure it dynamically. It's too much a complication.
Also, leakage subtraction process increases other noise sources, so it does not makes sense to do it unless leakage is by far the dominating noise source.
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Old December 19th, 2004, 02:47 PM   #3
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Dark current is the most important noise source in CCD cams, and strongly determines the dynamic range. The average (temp dependant ) component (DC component) is always substracted (black level reset). The AC component cannot be canceled (random) and it is this component that makes pics noisy at high gain settings. The HAD (hole accumulation diode) architecture from Sony significantly reduces dark current (AC an DC components).
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Old December 19th, 2004, 03:55 PM   #4
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Wow, thanks for the feedback guys.

I was not aware that dark current was tied so strongly to dynamic range. Very interesting.
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Old December 20th, 2004, 02:13 PM   #5
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<<<-- Originally posted by Andre De Clercq : Dark current is the most important noise source in CCD cams, and strongly determines the dynamic range. The average (temp dependant ) component (DC component) is always substracted (black level reset). The AC component cannot be canceled (random) and it is this component that makes pics noisy at high gain settings. The HAD (hole accumulation diode) architecture from Sony significantly reduces dark current (AC an DC components). -->>>

Actually, a portion of this AC component is not entirely random and can be subtracted, at least theoretically. For instance, some digital still cameras subtract this fixed pattern leakage noise component as measured from a dark frame exposure right after a shot taken.
However, it's more complex to implement this in video cameras.
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Old December 20th, 2004, 03:20 PM   #6
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Right Vladimir. Indeed in still camera's and industrial linear CCD scanners the fixed pattern noise and QE differences are being compensated in by automated lookup achitectures in order to get reliable imaging.
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