PHRubin wrote:
The noise floor depends on the technology and chemistry of both the sensor and processor. In real time here is no lower limit short of thermal noise. Processing can lower apparent noise.
Yes there is.
Total noise is the sum of 1) Dark Noise, 2) Read Noise, 3) Photon Shot Noise and 4) Fixed Pattern Noise.
1) Is generated because of electrons conducting because of the temperature being higher than absolute zero.
The value is exponential with temperature and is fixed by quantum effects once the technology is choosen
It is heavily related to the type of material and gate geometry... CCD, CMOS, FinFET, etc.
Bad thing is that by reducing the size of the gates, dark noise increases, because of quantum tunnel effects... we live in a strange Universe.
This is the reason because big telescope sensors are cooled to cryogenic temperatures (about 4K = -450ºF). You don't want to do that with your camera.
2) Is related to normal electric signal noise an can be traced back to shielding and - ultimately - to the decay of radioactive particles in the surrounding of the sensor.
It has been *very* minimized, and that is the main reason because modern cameras have lower noise than older ones.
We are almost at the bottom of it, and radioactive decay can already be identified in the noise signal... no not much more improvement in that department. Again, it is a quantum effect...
3) It is simply related to the fact that light comes in discrete photons.
Because the photons hit the sensor in an *average* correct number, but at inherently random quantities it depends only on pixel size (geometry) and exposure time (time)
Fo example, for typical 4um x 4 um modern pixels, the well capacity is about 60,000 electrons, and with a quantum efficiency of 50% this amounts to 120,000 photons... and at low light (maybe 20 foot - candles), and short exposure time (1/1000 s), the maximum amount of photons per pixels will be about 200 or 300... so slight random variations in the amount of photons received pixel to pixel (even a single photon) will be noticed when amplified or recovered in post.
There is absolutely no way to avoid this effect, it is encoded in the nature of light itself (quantum, quantum, quantum...) Shot noise is a *fixed* amount based on geometry, lighting and exposure time, and is *unrelated* to the composition or technology of the sensor. Once the size of the pixel is set, everything shot noise is set in stone.
4) Can be disregarded by calibration... either by the camera itself (high end cameras have a calibration file in firmware) or by taking "lights" and calibrating in post.
Bottom line: YES there is a *very* definitive floor for sensor noise.