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Estimation of Gaussian, Poissonian–Gaussian, and Processed Visual Noise and Its Level Function

We propose a method for estimating the image and video noises of different types: white Gaussian (signal-independent), mixed Poissonian-Gaussian (signal-dependent), or processed (non-white). Our method also estimates the noise level function (NLF) of these types. We do so by classifying image patches based on their intensity and variance in order to find homogeneous regions that best represent the noise. We assume that the noise variance is a piecewise linear function of intensity in each intensity class. To find noise representative regions, noisy (signal-free) patches are first nominated in each intensity class. Next, clusters of connected patches are weighted, where the weights are calculated based on the degree of similarity to the noise model. The highest ranked cluster defines the peak noise variance, and other selected clusters are used to approximate the NLF. The more information we incorporate, such as temporal data and camera settings, the more reliable the estimation becomes. To account for the processed noise, (i.e., remaining after in-camera processing), we consider the ratio of low-to-high-frequency energies. We address noise variations along video signals using a temporal stabilization of the estimated noise. Objective and subjective simulations demonstrate that the proposed method outperforms other noise estimation techniques, both in accuracy and speed.