What is dark noise subtraction/long exposure noise reduction?
Dark noise subtraction is a method for reducing noise in long exposures. First, the camera takes a photograph without the shutter open for the duration of the real exposure. This gives a map, as it were, of noisy pixels. Then the camera opens the shutter and takes the actual photograph. Once the photo has been taken the camera subtracts any noise present in the dark frame. Since both frames are taken under very similar conditions within moments of each other this is a reasonably successful technique of minimizing, but not eliminating, noise. Dark noise subtraction thus reduces noise from long exposures – typically night-time photography – at the cost of doubling exposure time and thus halving battery life. Some EOS digital cameras can use this technique automatically to reduce digital noise in exposures longer than a second or two. If your camera lacks this feature you can do it yourself manually using image editing software. A lot of amateur astronomers apply dark noise subtraction te
