Only the shot noise of the sensor has been considered in this calculation, on the assumption that the dark noise and readout noise are negligibly small.
Taking into account the detection limit, which is determined by dark current and readout noise of the CCD, as well as light collection efficiency, the minimum detectable number of photons on each pixel is estimated ca 100 phonon/s/cm2 on the surface of the subject under the measurement condition.
Fig. 4 Temperature dependence of the CCD dark counts through the readout electronics.
For the American FPIs using Andor CCD cameras, the readout and dark noise are more typically 3 4 electrons (r.m.s).
The readout noise and dark noise levels of this CCD camera are 6 electrons (r.m.s).
Dark current is 0.65 electron/pixel/h and readout noise in the slow scanning mode is less than 4.5 electron rms.
The dark current of Eq. (4), the readout noise (constant 2 counts), and the shot noise of incoming photon are accounted for.
The photodiodes, monolithically integrated (wire-bonded with a hybrid approach) on the IC, generate a photocurrent which is then ADC converted after subtraction of the dark component, thus allowing a convenient digital readout of the array.
Since the dark noise of the CCD camera is negligible compared with the readout noise, we use this value (three times of the readout noise) as a threshold to cut out the low-count data.
"Sorry, Not a Winner," the electronic readout said repeatedly and insensitively.
There are also sources of noise such as the readout noise of the digital camera and the dark current or background signal, which also affects the final contrast values [ 13, 14].
