Shot Noise
Definition
Random noise proportional to the square root of the number of photons captured. Shot noise is scene-dependent and cannot be predicted from the camera alone, but its statistical distribution (Poisson) is known and can be modelled.
- Scaling
- Proportional to the square root of captured photon count
- Statistical model
- Poisson distribution
- Dependence
- Scene-dependent, not predictable from camera settings alone
- Forensic use
- Modelled to detect regions with inconsistent noise in suspected image forgeries
Common questions
How does shot noise help detect a spliced or composite image?+
Because shot noise follows a predictable Poisson relationship to local brightness, an examiner can check whether the noise level in a given image region matches what that region's brightness should produce; a spliced patch pulled from a different image or from a denoised source often shows a noise level inconsistent with its own brightness, revealing the tampering.
Why can't shot noise be predicted purely from the camera model and settings?+
It depends on the number of photons actually reaching each sensor pixel during a specific exposure, which varies with the scene's own lighting and reflectance at capture time, not just the camera's ISO or sensor design, so the same camera produces different shot noise levels shot to shot.
Related terms
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- Specular Highlight
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