We propose a filter structure formed as the superposition of an impulse removal filter, based on a modified K-nearest-neighbor operation and discrete wavelet transform based noise reduction. This filter removes impulsive and Gaussian noise and mixed noises well. We also suggest an efficient architecture for implementing the impulse removal filter used in this structure.
Samvel M. Atourian, Karen O. Egiazarian, David Zaven Gevorkian, Jaakko T. Astola, "Combining the discrete wavelet transforms and rank-order based filters for image restoration," Opt. Eng. 37(1) (1 January 1998)