Noorbakhsh Amiri Golilarz - Department of Electrical and Electronic Engineering, Eastern Mediterranean University, Cyprus
Niyifasha Robert - Center for Cyber Security, School of Computer Science and Engineering, University of Electronic Science and Technology of China, China
Jalil Addeh - Department of Electrical Engineering, Babol Noshirvani University of Technology, Iran

Noise reduction is still a challenging problem for researchers. Many algorithms have been published in this subject and each finding has its own benefit and restriction. In this paper,a review of noise removing using some unique thresholding functions is conducted. All of these techniques used wavelet transform combined with thresholding functions for image de-noising. Their proposed thresholding functions have some properties like nonlinearity, continuity and smoothness. These functions were introduced to overcome the standard soft and hard thresholding functions and also to improve the performance analysis and enhance the visual quality of the images in terms of obtaining higher peak signal to noise ratio. Therefore, we can call these functions as improved version of standard soft and hard thresholding functions.

Noise reduction, Thresholding function, Image de-noising, Wavelet transform