What is the difference between hot, stuck, and dead pixels with regards to a camera's image sensor? What can cause each to occur? What can be done to reduce their influence on a photo?
Answer
Excitingly, these terms mean different things to different people. I think the most useful distinction is like this:
- Stuck pixels are always completely bright, as if they're fully overexposed
- Dead pixels are always off, as if receiving no light (these are usually less obvious)
- Hot pixels are not permanently stuck, but show up during long exposures (as the sensor heats up). These usually are defective pixels to some degree, and the same sensor will usually have the same hot pixels in the same conditions.
Some people use "hot" and "stuck" interchangeably, for either one or both of the different situations. I think it's more useful to make a distinction, but be aware that not everyone does — it's most helpful to be a little more verbose and explain what exactly you mean.
"Dark frame subtraction" is an effective way to deal with hot pixels. The same can be done for stuck (or dead) pixels, but generally the thing to do is have them mapped out permanently. Many cameras have a function in the menu to scan for these defects and do the mapping; otherwise, it's usually covered under warranty service. (This may or may not also get some or all of the hot pixels.)
In a digital sensor, all of these usually refer to a single photosite, with its corresponding color filter, so you might have a bright spot of red, green, or blue. This may also "bleed" into nearby pixels during the demosasicing process (but only as an artifact, not from electrical leakage or anything), resulting in + or × patterns.
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