Unwanted signal, such as salt and pepper noise, white gaussian noise, quantization noise.
Given a random variable x, its Probability Distribution Function (PDF) is p(x) with properties and .
We can think of p(x) as being the density of the values between x and x+Δx. That is, the probability of finding a value between x and x+Δx is p(x)Δx.
Suppose that input image is , output is as in
Consider the difference between g and f to be quantization noise, . For a simple quantizer, . In this case, quantization noise is uniform [0, 1) with pdf
Arises when photons are emitted independently and randomly, as in radioactive decay or very low light levels. If emission rate is m photons per unit time T, then the probability of observing exactly n photons is
Derived this as limiting case by dividing time T into N bins, such that either 0 or 1 photon is emitted in each bin.
Also, variance and standard deviation so signal-to-noise ratio (SNR)so the SNR goes up at higher emission / count rates.