“…The spatial filter do the denoising by multiplying different masks [13], averaging based on nonlocal self-similarity [14], carrying on the non-linear local filter [4,15] or using the local polynomial approximation [16,17] to get rid of the noise. The frequency filter removes the noise by using a low pass or high pass filter in the frequency domain [18,9,19]. The regularization method establishes a regularized cost function and restrain the noise by minimizing the cost function [20][21][22].…”