Image Stacking
Averaging multiple identical exposures to reduce random noise or to combine content across frames.
Formula / rule
SNR improvement = √n
Measured in
count
In depth
Because noise is random and signal is not, averaging frames cancels the noise while reinforcing the image — four frames halve the noise, sixteen quarter it. The same technique with a median rather than a mean removes transient objects such as passers-by, and it underpins deep-sky astrophotography entirely.
Examples in practice
Sixteen stacked frames of a night street scene give shadow quality that a single frame at that ISO could never reach.