Question for Bob - How was a hot pixel fixed on new 5D MkII?

[arthurc]

Just got my new 5D MkII and love it. After taking a bunch of pictures and pixel peeping, I noticed a tiny blue/violet mark in the same spot on all images. Found many examples that looked exactly the same on other forums, explaining that it was a hot or stuck pixel. One recommendation was to turn on manual sensor clean for 30 seconds but leave the lens in place. I tried and voila, problem solved. My question is, why did this work? Some people say the camera remaps the problem pixels but that seems pretty advanced to me, particularly as Canon doesn't advertise this. Is it just that the sensor clean function turns off power to sensor and "reboots" it? In any case I have the regular and extended warranty with a prolonged "lemon" clause, ie, if problems occur in the first few months, the camera will be replaced rather than repaired. Any ideas? I gather that 1 problem pixel out of 21,000,000 is not unexpected.

[Bob Atkins]

The answer to your question is "I don't know"!

There have been lots of reports that hot pixels (or stuck pixels) have "fixed themselves" after a similar process which usually involves activating the sensor clean function with a lens mounted and the lens cap on. Sometimes it's suggested that you first take a shot at high ISO with an exposure of a second or so.

I've seen claims it works on any EOS DSLR camera and other claims that it doesn't work at all. It's hard to separate truth from fiction here. Canon have never commented on the issue and what happens when it does work isn't really known.

Canon can "map out" bad pixels, but they don't say how they do it and it may involve some reprograming of internal camera memory. What then happens is that the value of any pixels which have been mapped are interpolated from the neighboring pixels.

So whatever is happening during the cleaning process, it certainly does no harm, so if you are bothered by hot/stuck/dead pixels you can't lose anything by trying it.