Dead Pixel? What Does That Mean?

I've seen some gear come up for sale and noticed the sellers will sometimes mention "dead pixels", as in "this camera doesn't have any dead pixels", or "this camera has a dead pixel, can be repaired".

Does a dead pixel refer to the viewing screen or the sensor or...? Please enlighten, and explain how one would see a dead pixel. Maybe someone can post an example, too?

A dead pixel is a single pixel on the sensor that doesn't work. If you want to find out how many you have, shut the lights off, put the lens cap on, and take 3 or so pictures at a long exposure. If you see red dots in the same place on each picture, those red dots are dead pixels. Every camera will likely have a few. My 7D has 18 million pixels and I think about 4 or so are dead. No big deal unless you take really low light pictures with long exposures and a tiny red dot bothers you. Easily fixed pp.

actually mckinley i believe is referring to something called "hot pixels" and any camera will have a few stuck or hot pixels on a long exposure shot, most start after 1" exposures.

A dead pixel, a truly dead pixel, is usually stuck and shows in every picture no matter how quick the exposure.

generally hot pixels are pretty easily mapped out by the factory, but as mckinley says, out of the 15.1 million pixels my camera has, I'm ok having 3 or 4 that stick in long exposure, at regular size its not noticable and if you blow it up it is quite easy to clone out

A pixel has multiple elements producing red, green, and blue filtered output. A "hot" pixel has all of its elements fully outputting signal--thus outputting a "white" signal. With a long enough exposure time and a high enough ambient temperature, any and every pixel will eventually go hot, although temporarily. Usually the term "hot pixel" is reserved for defective pixel that is always hot.

A pixel may also have faulty elements so that it outputs only a single color or combination. That's a "stuck" pixel--a one-color pixel.

Or a pixel could be totally defective and produce no output at all...it will always be black.

With the high resolution sensors of today, you don't usually notice a single defective pixel, unless you're doing a lot of pixel peeping at 100%. More often, if you see it in a photograph at a "real" enlargement, you're seeing a clump of defective pixels.

RDKirk wrote in post #10212374
A pixel has multiple elements producing red, green, and blue filtered output. A "hot" pixel has all of its elements fully outputting signal--thus outputting a "white" signal.

That's wrong, each pixel is either receiving either red, green or blue spectrum due to the Bayer filter in front of it.

A hot pixel will be red, green or blue depending which colour the bayer filter is "filtering"

A dead pixel is when there is no output however it will not be black unless there is no interpolation. That is if the 'green filter' sensor is dead, there still will be red and blue in your final image as those components are guessed (interpolated) from the surrounding red and blue pixels.

yep I meant hot pixel.

Come on guys we all know a dead pixel will get bigger as it implodes in on itself starting off a cascading effect where no light will be able to escape. As the cascading effect gets larger due to photovoltaic variables more pixels will be drawn in and in the end your sensor will disappear up it's own housing.

Nikolas wrote in post #10213554
Come on guys we all know a dead pixel will get bigger as it implodes in on itself starting off a cascading effect where no light will be able to escape. As the cascading effect gets larger due to photovoltaic variables more pixels will be drawn in and in the end your sensor will disappear up it's own housing.

then this happened: