What is a Hot Pixel?
A hot pixel is a defective pixel which remains constantly on, rather than cycling on and off like other pixels do. The term “hot pixel” is used both to describe defects in LCD screens, and to discuss problems with the sensors used in digital cameras. In both case, a hot pixel can vary from a mild problem to a source of extreme irritation, and the entire device usually needs to be replaced to cope with the problem. In the case of an LCD screen, a hot pixel shows up as a bright white dot, reflecting the fact that it is not reproducing the data sent to the screen correctly. It is usually difficult to see a hot pixel unless there is a dark background, in which case it may not be a major issue. By contrast, a dead pixel, which is stuck in the off position, will show up as a small black dot on the screen. Many screens develop hot pixels over time, with some manufacturers replacing their screens if hot pixels emerge while the screen is still under warranty. In a digital camera, a hot pixel in
It is simply a transistor on the camera sensor that gets overcharged when exposed to light for longer than normal periods of time. There are also “stuck” pixels (which are usually a bigger problem), which will be the same color in your photos no matter what. With 8 million tiny transistors in the Rebel XT’s sensor, you would have to be exceedingly lucky not to have a few performing slightly out of spec. But the fact is in almost all cases they should not be noticeable, and in cases where they are (such as long exposures), noise reduction will usually take care of them. It is possible to have what some might consider an excessive number of hot pixels, however; or you may have hot pixels that are visible nearly all the time. This would probably be unacceptable to most photographers. The way to test your camera for this is to take a 25 second exposure at the lowest possible ISO setting with the lens cap on. You’ll get a black frame, free of sensor gain noise, and you’ll pretty easily see
