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Old Jan 19, 2004, 12:37 PM   #1
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Default Question for Bob regarding FZ10 feature.

Although I could find no mention of it in the manual, I have discovered that the FZ10 employs noise reduction at slow shutter speeds. My question is, at what shutter speed does the NR begin to work?
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Old Jan 20, 2004, 11:36 AM   #2
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To the best of my knowledge, the noise reduction is inpart tied to the compression. I'm not aware of any change tied to shutter speed. Where or how did you read this?
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Old Jan 20, 2004, 1:53 PM   #3
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Default Re: In-camera noise reduction

After a picture is taken, the camera shows a message saying "Please wait". The duration of that message is identical to the shutter speed, so if you take a 1-second exposure, the shutter will close 1 second after you press the button, the "Please wait" message will immediately appear, and will remain visible for 1 second. If you use a 4-second exposure, the message will persist for 4 seconds after the shutter closes.
The camera doesn't need more time to process a 4 second exposure than a 1/2000 second exposure, so the reasonable explanation for the "Please wait" delay is that the camera is doing dark-frame noise reduction by repeating the exposure with a closed shutter, then subtracting the dark-frame from the image just captured while the shutter was open.
The question, of course, is whether this is the correct explanation of what's happening.
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Old Jan 20, 2004, 2:19 PM   #4
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Exactly as Charlie described. But no mention of it in any source that I could find.

Bob, try taking an 8 second exposure with the LCD on and you'll see what we're talking about. My Olympus also has this feature, but it is documented. I'd like to know at what shutter speed does the FZ10's NR kick-in.
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Old Jan 20, 2004, 3:58 PM   #5
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Definitely dark frame subtraction.
Does not happen in the burst mode.
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Old Jan 20, 2004, 5:25 PM   #6
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Default Re: In-camera noise reduction

Quote:
Originally Posted by Charlie Howard
the camera is doing dark-frame noise reduction by repeating the exposure with a closed shutter, then subtracting the dark-frame from the image just captured while the shutter was open.
"repeating the exposure with a closed shutter"? Since there is no exposure with a closed shutter, what information is the camera acquiring? I have noticed that same delay with the fz1. Can you explain dark-frame noise reduction a little further? Thanks
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Old Jan 20, 2004, 7:13 PM   #7
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Default Re: what is dark-frame noise reduction

First, to see what I'm (trying to) explain, put your camera in Manual mode and set aperture to f/2.8 and shutter speed to at least 1 second. Then, aim the camera at yourself so that you can peer into the lens and see the small open iris way inside. Zooming back & forth a bit may help you spot the iris.

Next, while watching the open iris, press the shutter button. The iris will remain open for the shutter time you've selected, then close for the same length of time, and then open again. The time during which it was closed is what I'm assuming is the "dark-frame" time.

During the dark-frame time, the CCD accumulates a charge in each of its sensors, just as it does while the shutter is open. If the CCD was entirely noise-free, nothing would accumulate and a perfectly black image would be captured. This is the same as what would happen if you left the lens cap on while taking a picture in a darkened closet.

Since no CCD is perfect, some charges accumulate even when there is no light. That's noise.

Since the conditions for taking the dark-frame image were identical in all respects but one to those for taking the actual image (the one difference being the availability of light), the assumption is that both images accumulated the same noise level in each pixel. Both images were taken at about the same time, same temperature, same duration; and the resulting signals were boosted identically to satisfy the ISO selection.

So, by subtracting the dark-frame readings from the exposed frame, we should wind up with an image that has much less noise. Obviously, this method does not work perfectly, because if it did, an ISO 400 picture would be completely noise-free, even better than what NeatImage or NoiseNinga can do.

Each pixel on the FZ10's sensor is about 2.5 micrometers on a side, (1/10,000 inch). It doesn't take much to give them some charge.

If you want to see an example of pure noise on ANY digital camera, take a long-exposure picture with the lens cap on, in a dark room (the lens cap is not perfectly light-tight). Bring it into your computer, then into a photo editor, and slide the bright end of the LEVELS control towards the left. Eventually, you'll begin to see some colored pixels. They tend to cluster. The closer you can get the LEVELS to "0" before you see anything, the less noise there is. If you take two of these "black" pictures, one at the camera's minimum ISO and the other at its maximum ISO, you will see a huge difference in the images as you slide their LEVELS from 255 towards 0.
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Old Jan 20, 2004, 7:37 PM   #8
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Well put Charlie! You saved me a lot of typing
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Old Jan 20, 2004, 9:07 PM   #9
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Why does it need to capture a dark screen every time?
a dark screen is a dark screen. Period.
They could very well program it into their NR logic and superimpose it within the processing.
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Old Jan 20, 2004, 10:15 PM   #10
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Not really, a CCD’s characteristics can change for a number of reasons: battery voltage, temperature, age and others.
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