Modified directional weighted filter for removal of salt & pepper noise

Switching median filter is a popular type of salt & pepper noise removal technique in recent years. It first detects noise pixels in an image, and then only restores the noise pixels by using the median or its variant of filtering window. Existing directional weighted median filters suffer their own deficiencies when detecting and restoring noise pixels. In this paper, after deeply analyzing the reasons that cause the deficiencies, we propose a modified directional weighted filter to alleviate the issues. The new filter first detects salt & pepper noise by combining existing directional gray level differences with additional judgment of gray level extremes. Then the noise density of each noise pixel's non-recursive local window is estimated, and an innovative weighted gray level mean of a recursive or non-recursive filtering window is taken as the restored gray level according to noise density. Experimental results on a series of images show that the proposed algorithm achieves significant improvements in terms of noise suppression and detail preservation, especially when the noise density is high.