Study of Defog Technology Based on Scattering Model in Assistant Driving System

This paper firstly analyzes a typical defog algorithm. Directly towards assistant driving system, Monocular Camera Machine Vision and Atmosphere Scattering Model are combined to construct the scene depth map by linear imaging model. At last, the image was restored by atmosphere scattering model. With RETINEX algorithm, this method has a better effect in different distance: the error of depth map increases along distance increasing; two factors on the algorithm precision: the installing height and pitching angle of camera. Finally, point out that next stage we will estimate the error coursed by extrinsic parameters by experimentation. The image defogged technology researches are focused on these fields: 1. Histogram equalization algorithm 2. Defog and resume color contrast for the image based on the color constancy theory 3. The recover method based on physical model. The first two methods above could both promote the contract of image in fog day in a certain extent, but the reduction of the image contract in fog weather and the distance between object and camera has a non-linear increase relation, the degradation of the image point is different along with the different depth of field of the correspond scene point. Therefore, some shortcomings such as over processing or lack processing, and could not be restored for all the different distant scene point in one picture. The algorithm based on the model is called image restoration; this method is based on the physical theory of image degradation, which could recover the different distance scene information. The representative research based on physical model is presented as follow: Oakley, JP presented a multi-parameter degradation model, in which, depth map could be acquired by radar, scene could be recovered by offering the attenuation and optical scattering. Although it is efficient for improving the quality the degraded image when using Oakley module, the needs of imaging system parameters precisely and expensive equipments makes it applied in practicality hardly. Narasimhan, SG (1)(2) restored the integrative depth map and chrominance by attenuation- airlight model without atmosphere and scene depth information, all they need are two different weather condition images to restore the scene structure and depth information. As the attenuation is different under the different weather condition, they construct the depth map by subtracting one image from the other image under different weather condition. And then they presented depth estimation algorithms interactively to remove weather effects from a single image. But this algorithm cannot be applied in dynamic scene such as driving environment. By the analysis above, the key factor of defog algorithm based on model is the depth map construction, so how to construct the depth map becomes the key point of the recovering algorithm. In this article, a distance map construction method based on a linear imaging module is proposed, directed mainly at the special configuration of vehicle road. The corresponding relationship of scene view and CCD target surface is established, through the vehicle camera calibration, which could resolve the difficulty of distance figure construction in atmosphere scatter module defog and the costly equipment. With this easy and effective method, a good recover effect for the fogged image of speedway and other highways could be got.