Signal-to-noise ratio
The signal-to-noise ratio (often abbreviated SNR or S/N) is the ratio between the maximum signal and the overall noise, measured in dB.
The maximum value for SNR is limited by shot noise (that depends on the physical nature of light, and this is inevitable) and can be approximated as
SNR limits the meaningful grey levels in the conversion between the analog signal (continuous) and the digital one (discrete).
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