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08-04-2008, 02:36 PM   #1
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Hot pixels

Nice clear sky this evening so I thought I would take some long exposures of whisps of clouds and stars. It wasn't quite dark so I used 10s with my CZJ 35/2.4 Flektogon at f/2.4. Noise reduction was off.

When I got the pictures back inside and viewed them on my monitor they looked nice: deep blue sky, whisps of lighter blue and pinpricks of light. The I flipped to the next one, I took in another direction. "Oh that star has gone out, but the others are still there". Hmm. I flipped to the next one, in another direction. "Oh those 'stars' are in the same place!". Somthing is fishy!

So apart from the one star that disappeared, the rest must be hot pixels. Oh dear. So I then took a photo with the lens cap on with NR on and with NR off. With NR on the entire frame is black. With NR off those same "stars" are back. I don't see any noticeable hot pixels on daylight photos.

Now my question is this. I see about 13 very bright, 10 less bright but visible, and another 10 that are faint. Is this acceptable? If not, then what can be done about it? Bear in mind that my camera is out of warranty (just) and that I have not done a test like this before so I don't know if it is recent or whether the sensor was always like this.

Richard

08-04-2008, 03:52 PM   #2
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This happens to all digital camera sensors to some degree when doing long exposures, it's normal. The camera will ordinarily compensate for this by doing dark-frame subtraction (it takes a second exposure the same length as the first, except with the shutter closed, and then factors any hot pixels out of the resulting picture).

This means when doing long exposures your options are the following:

1) Let the camera perform dark-frame subtraction and simply take a bit longer taking the photos
2) Photograph in RAW and run the result through a good RAW developer, most of them are pretty good at removing hot pixels.

Again, I must stress that it is perfectly normal, and all cameras will do this.
08-04-2008, 05:59 PM   #3
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Hi All

I have a Samsung GX10 which had hot pixels after 4 months of use.
I sent it back to samsung and they replaced the camera for me.

Personally i wouldn't stand for hot pixels if the camera was under warranty - the same as when buying an LCD TV or monitor..etc

not sure how visible your hot pixels are but i had 3 and they were pretty visible on the image when i had uploaded it off the camera
08-05-2008, 05:29 AM   #4
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QuoteOriginally posted by sammyvalencia Quote
Hi All

I have a Samsung GX10 which had hot pixels after 4 months of use.
I sent it back to samsung and they replaced the camera for me.

Personally i wouldn't stand for hot pixels if the camera was under warranty - the same as when buying an LCD TV or monitor..etc

not sure how visible your hot pixels are but i had 3 and they were pretty visible on the image when i had uploaded it off the camera
If they showed up in every picture, then they were stuck pixels, not hot pixels.

Hot pixels are transient and will go away when the sensor cools down, and they are not always in the same positions.

08-05-2008, 05:50 PM   #5
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QuoteOriginally posted by alohadave Quote
If they showed up in every picture, then they were stuck pixels, not hot pixels.

Hot pixels are transient and will go away when the sensor cools down, and they are not always in the same positions.
ahh! thanks for clearing that up!

They would have been stuck pixels!
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