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Old Aug 31, 2004, 2:52 PM   #1
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I take a photo use long time exposure (ISO50 10") and found a lot ofhot pixel !
Do you think this is a z3 serious problem?

Pic#1
ISO50 F/5.6 10" @2MP
http://img55.exs.cx/img55/8953/PICT0118.jpg

Pic#2
ISO50 F/4.0 10" @2MP
http://img55.exs.cx/img55/4365/PICT0124.jpg

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Old Aug 31, 2004, 3:11 PM   #2
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At such a long exposure hotpixels are normal. However noise reduction should remove these. Was it turned on?
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Old Aug 31, 2004, 3:12 PM   #3
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Turn on your noise reduction. That's what it's for. There should be a menu choice under Setup for Noise Reduction on/off.

You'll have hot pixels on virtually all cameras with longer exposures. Noise Reduction is designed to mask them out using a "Dark Frame Subtraction" process.


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Old Aug 31, 2004, 3:53 PM   #4
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Thanks for your suggestion ^^
But i already turn Noise Reduction on

As Z3 SPEC Min shutter = 15s (Bulb 30s).
I assume that hot pixel should be not happen in ISO50 10".

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Old Aug 31, 2004, 4:12 PM   #5
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I made a 10" test, I see a few hot pixels, but not as much as you:

http://www.csucsposta.hu/jbnd007/PICT0431.JPG

Are you sure NR is on? Does the camera display "Processing" for another 10 seconds?
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Old Aug 31, 2004, 4:17 PM   #6
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I'd reset the camera back to factory defaults (there should be a menu choice for this under Setup somewhere). Let the camera cool off good, then try it again. Heat will impact noise levels and hot pixels.

Here's the deal:

Your camera has a noise reduction system that is designed to subtract hot pixels from the final image on longer exposures. It actually takes 2 photos, using the same exposure settings (that's why it takes twice as long to process the images after a certain shutter speed or slower). One image simulates having the lens cap on (shutter remains closed). On longer exposures (anything much over a second), this image will contain lots of hot pixels. The second image is of your actual subject. Then, it compares the images, and uses interpolation techniques to replace the hot pixels in the final image from values found in adjacent pixels. This has the effect of masking out the hot pixels. This is known as "black frame subtraction".


It knows where to find them in the actual image of your subject, because most of the time, hot pixels will show up in the same locations if the camera settings are the same. But, it can't always be right. That's why it can miss some (some pixels may show up as hot in your subject photo that don't in the black frame photo, and vice-versa).

On a typical 4 or 5 Megapixel Sensor, with noise reduction disabled (as you can in some models lke yours), it's not uncommon tohave adozen or more hot pixels on a 1 second exposure. With a 10 second exposure, it's not uncommon to have hundreds of hundreds of hot pixels.

That's why the CCD's have cooling systems when used for astronomy (a cooler CCD will have less hot pixels on longer exposures).

Basically, if you do not have any pixels that are hot at typical shutter speeds (about 1/30 second or faster), then you have nothing to worry about. These are known as "stuck pixels" when they remain hot at all exposure settings.

Up until recently, cameras did not even have noise reduction systems to help find and remove hot pixels on longer exposures. So, you had to do the black frame subtraction using software. You took a photo with the lens cap on. Then, you immediately took the photo of your subject using the exact same settings. You can't wait too long between them, because the pixels that are hot can change rapidly with temperature and other factors).

Then, you used software to compare the images to remove the ones that showed up in the "black frame" photo from the photo of your subject.It can't always work perfectly (but it's usually close enough to remove most of them on exposures that are not too long).

So, it sounds to me like something is not right with the camera's noise reduction system (as if it's disabled, or your camera is very hot, so the hot pixel locations are changing drastically between the two frames). Reset it to defaults, let it cool off, then retest.
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Old Aug 31, 2004, 5:35 PM   #7
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JimC wrote:
Quote:
Reset it to defaults, let it cool off, then retest.
I still get a lot of hot pixel !!

Theseare my lastest test.

"Low light environment, ISO50 15" F/5.6 @2MP Fine"
http://img71.exs.cx/img71/5568/PICT0150.jpg

"Lens cap on, ISO50 15" F/2.8 @2MP Fine"
http://img2.exs.cx/img2/4711/PICT0154.jpg

Should igo to claim it withreseller?
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Old Aug 31, 2004, 5:48 PM   #8
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That's up to you. You may get one that's even worse. Most manufacturers are not going to replace a camera because of hot pixels at longer exposures (only for stuck pixels at normal exposures). That's because virtually all cameras will have hot pixels at longer exposures (especially cameras with smaller, denser CCD's). Sometimes the noise reduction finds them all, sometimes it doesn't.

The longer the exposure, the more likely it will have hot pixels that show up (since the chance of the hot pixels being in exactly the same place on both the dark frame, and the actual frame, decreases as exposure times get longer)..

Your lens cap on photo had 127 hot pixels with a luminance value over 60 (the typical threshold for filtering noise versus hot pixels).

What is it like at shorter exposures? 1 second, 2 seconds? Is the camera cool when you are performing the test?

I'd make sure anti-shake is off, too (this can cause the CCD to heat up, increasing noise).


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Old Aug 31, 2004, 6:12 PM   #9
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I feel so bad. Buying Z3 is my wrong decision.

In conclusion,I think that my Z3(maybe all Z3)can't use long time exposure, whileCanon S1 work with longer exposure

Anyway, thanks you for great infomation
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Old Aug 31, 2004, 6:34 PM   #10
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Hi!

I also made a test:
ISO 50
F/2.8
10"
@4MP

http://www.8ung.at/ernstl/testz3/PICT0341.JPG (687kb)

I think thats ok.
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