The Research Of Contrast Enhancement Methods Of Fog-degraded Images

With the wide application of the digital surveillance system in every region,the demands of system's reliability and stability have increased.However,because of the atmosphere scattering phenomenon,the contrast and color of the image captured by surveillance system in fog are significantly degraded which greatly reduces the practical value of the image.Based on the analysis of the mechanism of imaging in fog,this paper conducts a full investigation into the enhancement of fog-degraded images from the point of digital image processing.The work includes:(1) Research based on the enhancement of indirect contrast.One of the most important features of fog-degraded images is that contrast degraded is closely related with depth.According to this,adaptive histogram equalization is used to enhance the local information of images.Methods including local HE,removing sky local HE, POSHE are deeply analyzed in detail.By comparing these methods,this paper put forward a new method which is more useful in practical applications.The experimental results verify the effectiveness of the method.(2) Research based on the enhancement of direct contrast.The fog-degraded images usually have lower contrast and fuzzy object boundary,by combining the merit of fuzzy theory for uncertain information,this paper proposes a novel fog-degraded image clearness algorithm based on fuzzy contrast enhancement.This algorithm is effectively applied to contrast exponential degrade law in fuzzy contrast measure modification which can perform fog-degraded image enhancement adaptively.(3) Research based on the enhancement of the colorful fog-degraded image. Contrary to colorful fog-degraded image,the paper studies the image enhancement methods in different color spaces based on the invariability of hue.In the RGB color space,images are transferred both in RGB and CMY color spaces,the enhancement methods of gray image are generalized to the colorful fog-degraded image.In the HIS color space,the intensity are enhanced by the enhancement methods in gray scale,the saturation is stretched and the hue is kept invariable.