Enhancement Algorithm Of Image Based On Retinex Theory In The Wavelet Domain

Image enhancement as an important pre-processing means has gained much attention by many people because of its widely used. Image enhancement is purposefully emphasized the gloable or local image pixel value features to improve the visual effect or to meet the specific analysis. Retinex theory and related algorithm is new idea of image enhancement.Retinex method is theoretically based on the color constancy of human visual system. The basic strategy is simulating the process of human vision to enhance image contrast and resume true color of object.This paper proposed a new Retinex algorithm and JPEG2000 compression framework by analysising the traditional Retinex algorithm and wavelet multi-resolution features. Secondly a new method to enhance JPEG2000 compressed image is proposed, in which Retinex theory is introduced into JPEG2000 compressed frame.The main content of this thesis is shown as follow:1.Based on the view of selecting the path of pixels comparison, Common Computational Strategies of Retinex algorithm has been analysised, including Retinex algorithm based on random paths, the McCann's Retinex algorithm based on iterative calculation, the Retinex algorithm based on center/surround, Then this paper pointed out characteristics and limitations of Retinex algorithm, and verified in experiments.2.Because of the problem that the traditional enhancement algorithm can not suppress the noise effectively when enhanced the image. This paper proposes a novel algorithm of estimating the image illumination and noise in the wavelet domain based on Retinex theory. By using the feature of the wavelet multi-resolution, algorithm suppress the volatility of the low-frequency coefficient and use the model of multi-subband independent coefficient to estimate the high-frequency coefficient, at the same time using soft-hard estimated method to suppress the image noise. The experimental results show that the algorithm can extract the image illuminate vector effectively, but also can suppress the image noise and adapt in different foggy weather.3.In the base of recently research for image enhancement algorithm in the compressed domain, we introduce the Retinex theory into the JPEG2000 code process to achievie the goal for enhancement the JPEG2000 compression image. The procedure may divide into two steps. First, using the Retinex algorithm to carry on the enhancement; Secondly,improving the Luminance quantification table.It take the Retinex theory as the foundation,regarding the DC coefficient of DWT coefficient as the incident light component and the AC coefficient of DWT coefficient as the reflected light component.the goal for revises the DC coefficient is to adjust the scene illumination condition and for the AC coefficient is to enhance the image contrast gradient,then judging the activity of the great block to adjust the luminance quantification table adaptively to achieve the goal of preserving enhancement detail and suppressing the massive effect.