Black Frame Equivalent Noise Reduction
Many DSLR’s are capable of something called black frame equivalent, which is camera’s internal noise-reduction feature. When the feature is enabled, the camera will firstly take an exposure with the given parameters shutter closed, so that the signal the sensor reads is essentially consisted only of the electronic noise (the combined effects of varying electron density in a electronic stream, and the manufacturing quality of the components of a sensor. Also the individual pixels of the sensor cause interference to the neighboring pixels due to these reasons.). After this step the image is exposed shutter open, and the signal values of the black frame exposure are suppressed from the exposed image. Of course the black frame equivalent method cannot account for the noise caused by statistical fluctuations in the photon density of the incoming light at the given exposure time, so always some image noise will remain. However, in effect this noise reduction technique is inherently far more superior compared to the post-production methods available, and in certain situations it might be better, when a certain degree of image detail loss is acceptable. A good example of this is night-time photography, especially astronomical photography, where there is not much detail in the sky. If the image consists of other elements, for example bodies of water or ground, these can be exposed with lower ISO-settings and longer exposure times if the atmospheric conditions allow, without using the black frame equivalent method to preserve as much detail as possible.