The Research Of Underwater Image Enhancement

With the development of economy and society,ocean gradually becomes a new space for development around the world.In the exploration and exploitation of marine resources,and marine environment monitoring,the acquisition and processing of underwater optical image is one of the important means of ocean research.However,subject to the special imaging environment,light absorbed selectively and scattered strongly underwater,the quality of underwater images generally will be significantly degraded.Therefore,underwater image processing is of great significance.In this context,this paper carried out the research of underwater image enhancement technology.The selective absorption and scattering of water will cause a very serious impact on underwater imaging.In this paper,we analyze imaging principles of underwater images,optical characteristics of water body and underwater image degradation reasons from the respect of basic theory.We study on the common image enhancement methods,comprising gradient field compression method,histogram processing method and dark colors priori method.And the analysis of deficiencies of these methods when they are applied to the underwater image enhancement is made.In this paper,we propose an improved enhancement method for underwater color images.First we convert an underwater color image to Lab space,and apply multi-scale Retinex to the luminance channel,i.e.,L-channel for image defogging;and then we apply the CLAHE to the defogged image to enhance image contrast;then we adjust the color channel,i.e.,a and b channel to correct the tone of the image,and convert the image back to the RGB color space last.In order to verify the effectiveness of the proposed algorithm,we use gray contrast and histogram entropy to evaluate the contrast information,use edge density and phase coherence to evaluate the clarity information,and use the RGB histogram to evaluate the color information of the image.In this paper,practical underwater imaging experiment results and enhanced image were evaluated,and the results of proposed algorithm and other common enhancement algorithms are compared,and different types of underwater images are selected to verify the proposed algorithm.Results show that the proposed algorithm can effectively improve underwater image clarity and contrast,and remove the common blue-green hues of underwater images,so as to achieve the purpose of image enhancement.