Hot pixels?

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Hot pixels?

Postby Photopotamus on Mon Jun 29, 2009 11:48 pm

All,

Just a question... I have noticed that when I'm taking shots with long exposure times, I seem to have a few "hot pixels". Since they seem to "move around", and are not "fixed", I assume that they're not dust. Also, they are frequently a single colour (green & magenta mostly).

The bit of Googling I've done suggests that while this phenomenon is inherent to all sensors, those with higher pixel densities (like mine) are also more susceptible. So my questions are:

Is this something we just learn to deal with in post (clone out, etc)?

Is it an issue that you run into frequently? Maybe there's something wrong with my technique...? :oops:

Thoughts & comments appreciated.
Canon 450D/ 18-55 IS "Kit Lens" / 55-250 IS "Kit Lens 2" / 17-85 EF-S / Nifty 50 II

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Re: Hot pixels?

Postby gstark on Tue Jun 30, 2009 12:04 am

You are spot on in your diagnosis of these as being hot pixels, and it's an issue directly associated with shooting for longer exposure times.

In terms of "longer exposure times", could you please quantify this? (how long?)

Canons generally handle this problem better than Nikons, but if your exposure times are pushing the edge, then this may well be something that you're going to have to learn to address in your workflow.

Let's also come back to basics for a moment: what are you shooting? do you need to use long exposure times?
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Re: Hot pixels?

Postby surenj on Tue Jun 30, 2009 2:32 pm

Photopotamus,

Are you referring to photos taken during the VIVID walk?

Also some examples would be useful.
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Re: Hot pixels?

Postby JC_Denton on Sun Aug 02, 2009 12:45 pm

Some postprocessing software (such as Ligthroom) automatically detects and removes hot pixels from RAW files. In my experience Lightroom has been very good at this, there are also some free applications that do something similar like this http://www.pixelfixer.org/

Many DSLRs also have a long exposure noise reduction feature, which means the camera will take a second exposure without opening the shutter in order to work out where the hot pixels are, and then subtract them from the previous exposure. I have never used this feature myself, so I'm not sure how well it works or whether it works on RAW files.

Another way of reducing hot pixels is apparently cooling the sensor in some way, but this is risky as far as I know, and is mainly used by astronomical photographers for really long exposures.
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