The luminosity is the signal: > difference in luminosity across features and not the absolute luminosity This is exactly what signal to noise ratio refers to

The luminosity is the signal: > difference in luminosity across features and not the absolute luminosity This is exactly what signal to noise ratio refers to in my previous comment. The best solution is what the iPhone does: it is a 3d sensor that produces a depth map (think each pixel represents a distance to the object). But that's not really viable when trying to use normal security cameras.