An improved fog-degraded image enhancement algorithm

In fog weather, Images captured by outdoor surveillance system degrade significantly and suffer from poor contrast. This paper presents an improved algorithm for enhancing fog-degraded image contrast in which a moving mask is used. By assuming the pixels in a mask having same scene depth, the algorithm applies the modified partially overlapped sub-block histogram equalization to implement contrast enhancement in every mask. It involves two steps: first, sky region is segmented in order to restrain over-enhancement in the flat region and reduce noise; then, remove the sky pixels in masks and modify the histogram information in mask, thus the modified partially overlapped histogram equalization transformation function for enhancement can be gotten. This paper also proposes a novel fuzzy edge detection algorithm to evaluate above contrast enhancement effect. Experiments on many fog-degraded images demonstrate that the proposed improved algorithm is simple and effective in contrast enhancement of fog-degraded images.