Uncertainty in Phase Measurements ◾ 303
9.4.3 Signal-Dependent Contributions
9.4.3.1 Shot Noise
In a photon detector (charge-coupled device [CCD] and complementary
metal-oxide semiconductor [CMOS] cameras, photon counter), the num-
ber of electrons per exposure varies according to Poisson statistics, even
with constant average irradiance. e variance of the signal caused by shot
noise is proportional to the signal itself [16] when signals are measured in
electrons or counts [cnt]:
=(, [cnt]) [cnt]
2
uSshot S (9.8)
e full well depth of a pixel describes the maximum number of electrons
the pixel can hold, with typical values less than 10
5
. is leads to a shot
noise level greater than 0.3%.
9.4.3.2 Illumination Instability and Camera ...