Dark-frame subtraction

In digital photography, dark-frame subtraction is a way to minimize image noise for photographs shot with long exposure times, at high ISO sensor sensitivity or at high temperatures. It takes advantage of the fact that a component of image noise, known as fixed-pattern noise, is the same from shot to shot. Noise from the image sensor include defective pixels, which light up more brightly than other pixels, based on the amount of received light. The technique works by taking a picture with the shutter closed and subtracting that electronically from the original photo exhibiting the noise. In digital photography, dark-frame subtraction is a way to minimize image noise for photographs shot with long exposure times, at high ISO sensor sensitivity or at high temperatures. It takes advantage of the fact that a component of image noise, known as fixed-pattern noise, is the same from shot to shot. Noise from the image sensor include defective pixels, which light up more brightly than other pixels, based on the amount of received light. The technique works by taking a picture with the shutter closed and subtracting that electronically from the original photo exhibiting the noise. A dark frame is an image captured with the sensor in the dark, i.e., with a closed shutter or the lens and viewfinder capped. Such a dark frame is essentially an image of noise produced by the sensor. A dark frame, or an average of several dark frames, can then be subtracted from subsequent images to correct for fixed-pattern noise such as that caused by dark current, but it also works for removing what is called amp glow, portions of the sensor lighting up due to internal heat sources. Dark-frame subtraction has been done for some time in scientific imaging.