Dead pixel test

Click on the photo to see a larger sample. This was taken with a 13 sec exposure.

The CCD's in digital cameras may have some flaws where certain pixels may be "on" when they shouldn't be. These pixels show up when the camera heats up or when using long exposures. Here's an extreme example of my camera's hot pixels (and some dead pixels) before I sent it in to be fixed. The picture should be completely black, but some pixels have the wrong value and are various colors. Some newer cameras are actually set up to block hot pixels so they don't show up in pictures. You can use the Dead Pixel Test to check your camera for hot or dead pixels.