  The behavior of photons is controlled by quantum mechanics, not as
deterministic as classical optics shows. To this end, we defined a new
statistic $Z$, which is equal to the variance minus the expectation or mean.
Then, we established a statistical model for imaging systems and obtained three
fundamental imaging formulas. Among them, the first formula is entirely
consistent with the classic convolution equation. The second and third ones
link the $Z$ quantities of the object and noise elegantly with the $Z$ image
and covariance image, revealing new laws. Consequently, besides the flux
density, the $Z$ quantity of an object is also imageable, which opens a new
realm for imaging systems to explore the physical world.
