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Noise Sources
All electronic circuitry generates undesirable noise. The effect
of this noise on performance is described by the signal-to-noise
ratio (SNR). Photon noise, preamplifier noise and dark current
noise are the three primary sources of noise in a CCD camera.

Photon Noise

Photon noise, also known as photonic or photon shot noise, is
a fundamental property of the quantum nature of light. The total
number of photons emitted by a steady source over any time interval
varies according to a Poisson distribution. The charge collected
by a CCD exhibits the same Poisson distribution, so that the noise
is equal to the square root of the signal. Photon noise is unavoidable
and is always present in imaging systems; it is simply the uncertainty
in the data.

Preamplifier Noise

Preamplifier noise, also called read noise, is generated by the
on-chip output amplifier. This noise can be reduced to a few electrons
with the careful choice of operating conditions.

Dark Current

Dark current, or thermally generated charge, can be measured and
subtracted from data, but its noise component cannot be isolated.
Dark current noise is of particular concern in low light applications.