Research On Image Enhancement Algorithm Based On Retinex Theory And Block Fusion

Image enhancement is a research hotspot in image preprocessing stage.Common approaches to image enhancement include linear transformation,gamma correction,histogram equalization,histogram matching,unsharp masking,homomorphic filtering and Retinex algorithm.Among them,the Retinex algorithm can compress image dynamic range and enhance image details effectively and has a good color fidelity effect.An image enhancement algorithm based on block fusion and Retinex theory is proposed to overcome the disadvantages of Single-Scale Retinex algorithm about halo phenomenon and grey phenomenon.For the halo phenomenon,the illumination image of an original image is estimated by Gaussian weighted bilateral filtering instead of Gaussian kernel function,which can remove the halo phenomenon effectively.For the problem of grey,the nonlinear transformation and image fusion technology are introduced into the process of image enhancement.There are several steps in the process of image fusion proposed in this paper.In the first place,the reflection image is stretched by nonlinear transformation and the threshold of bright and dark areas of the stretched image are determined by Otsu threshold segmentation algorithm.Then the optimal parameters for bright areas and the optimal parameters for dark areas are determined by adjusting the parameters of nonlinear transformation and Retinex theory according to information entropy,and the local optimal images are gained according to local optimal parameters.Finally,the original image,the optimal image for bright areas and the optimal image for dark areas are fused by optimal fusion algorithm,and a consistency verification method is introduced to remove the blocking effect caused by optimal fusion algorithm.Experimental results show that the new algorithm can get the details of an image,remove the halo phenomenon and overcome the grey problem effectively.The new algorithm has a better ability to enhance images compared with Single-Scale Retinex algorithm,the Retinex algorithm based on bilateral filtering,histogram equalization and unsharp masking algorithm.The new image enhancement algorithm has strong robustness and can enhance non-uniform illumination images,low-contrast images and fog-degraded images effectively.