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Author Topic: Questions about dead pixels  (Read 2492 times)
Jonathan Wienke
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« on: April 21, 2003, 10:48:26 PM »
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Dead pixels are not generally considered acceptable. When taking pictures in low light with high ISO/low shutter speed, many digicams will exhibit hot pixels, but they vary from shot to shot, and are just an advanced form of noise. If I had a camera that always had a bright green pixel in the middle of the image, I would consider it defective and return/exchange it.
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Paul Caldwell
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« Reply #1 on: April 24, 2003, 10:18:58 AM »
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The issue of stuck pixels or Dead pixels is handled different by all companies.

The Stuck pixel is always on, so you get a solid red, green or blue. A dead pixel is white and will often bleed light onto the surrounding pixels.  A dead pixel is much worse than a stuck pixel.

Also many of the digicams I have used get Stuck pixels on longer exposures and this is very common and considered OK.  Most of the companies now have some from of dark frame subtraction to help get around this.  

If you are shooting a camera that is getting the same pixel stuck or dead on every exposure, then if the camera is still under warranty, for sure I would consider having it fixed.  It doesn't bother me that much to take it out as in most of my shots I am more worried about dust.  Never have been able to get all the dust off my 1ds.  

Paul
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Robert Roaldi
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« Reply #2 on: April 20, 2003, 10:07:07 PM »
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I asked similar questions on photo.net recently. I am not a digicam owner but this issue strikes me as important and under-discussed. I may just have looked in the wrong place.

I have occasionally read about dead pixels on digicam sensors in the context of how to fix them via computer image editing. But generally speaking there is not much written about the topic nor have I noticed it much in the context of digital workflow.

I wondered about a few things. Some people express the opinion that having a few dead pixels is normal and acceptable and that fixing them in an image editor is part of the game. Is this true? I'm asking that in the engineering sense, i.e. is there no way to produce dead pixel free sensors at a cost that makes digicams affordable (relatively)? If I buy a digicam with a dead pixel is it reasonable to ask for an exchange or am I chasing the holy grail?

If it is a commonplace phenomenon, then I wondered why it's not mentioned much in discussions of workflow. Do the algorithms in the sensors' firmware mask the pixels with interpolated data so that the user mostly does not know about it? At what point in the processing does this happen: A/D conversion on chip, conversion of RAW data, etc?  

I find it hard to believe that people think it's normal to spend time fixing a known set of bad pixels on EVERY frame. Seems like time badly spent.

Does the problem get worse over time? This may become important as more and more people buy 2nd hand digicams, like I am apt to.

How many dead pixels are deemed acceptable, 5, 25, 1000, 10,000? It would upset me if I paid for a 4 meg sensor but later found out that only 3.5 meg of them worked and that the rest consisted of interpolated data.
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James Pierce
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« Reply #3 on: April 22, 2003, 06:32:16 AM »
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This is an interesting question - I hadn't really considered this effect for cameras.  With laptops up to 6 dead (usually green) pixels is considered ok.  After that you are entitled to a new screen.
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