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Old Jan 21, 2004, 10:09 AM   #11
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OK..
I understand though I don't have an answer. Let me see what I can find out. It may take a day or two...
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Old Jan 21, 2004, 11:09 AM   #12
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Quote:
Originally Posted by Guerito
Not really, a CCD?s characteristics can change for a number of reasons: battery voltage, temperature, age and others.
umm....but wouldn't it be better to have a perfectly dark black image to superimpose in an effort to reduce noise?
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Old Jan 21, 2004, 11:21 AM   #13
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Quote:
Originally Posted by chiks
umm....but wouldn't it be better to have a perfectly dark black image to superimpose in an effort to reduce noise?
When you have the same noise characteristics in the picture and the dark frame, you can subtract one from the other and arrive at a cleaner result.
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Old Jan 21, 2004, 12:05 PM   #14
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Quote:
Originally Posted by chiks
Quote:
Originally Posted by Guerito
Not really, a CCD?s characteristics can change for a number of reasons: battery voltage, temperature, age and others.
umm....but wouldn't it be better to have a perfectly dark black image to superimpose in an effort to reduce noise?
No, that's exactly what you *don't* want. You would end up with bright and dark pixels all over the photo. You would be surprised at how much each photo cell can differ from its neighbor.
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Old Jan 21, 2004, 6:43 PM   #15
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Default Re: dark-frame noise reduction

Each pixel in a perfectly black image would have a value of zero (no noise), so subtracting it from the real image wouldn't change the real image. What you want is an image of the noise itself, which by definition includes non-zero values (if they all were zero, there would be no noise).

As Guerito and I have explained, the noise values are not constant in a CCD: they change in response to aging, the environment (e.g., temperature), and the exposure time. Also, when you or the camera selects an ISO value, the signals (and the noise) from the CCD are boosted accordingly. The dark-frame method dynamically captures most of the effects those things have on the CCD in the moment just after the actual image was taken.
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Old Jan 21, 2004, 7:41 PM   #16
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ah! now I get it.

Thanks for bearing with me and taking the effort to explain it to me.
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Old Jan 22, 2004, 6:01 PM   #17
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Question was sent, I hope to have a response by Monday.
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Old Jan 22, 2004, 10:00 PM   #18
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OK, thanks Bob.
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Old Jan 23, 2004, 8:46 AM   #19
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Guys,

I did an experiment to check whether this is dark frame subtraction.
The results were very educational.

Check the FAQ and try it yourself.
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Old Jan 27, 2004, 12:33 AM   #20
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Alexo, I couldn't find the testing on your site. Can you provide a direct link?
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