Automatic focus image method and system implementationabstractModern science and technology have been developing rapidly, in order to quickly and accurately to tiny image collection, treatment and automatic, digital automation to put forward higher request, one of the key problems is automatic focus. Because of the theory of digital image processing, and perfect gradually mature automatic focusing system has been based on optical system of automatic focus gradually transformed into based on digital image processing of automatic focus. In order to improve equipment performance, this paper automatic focus technology is studied, including the auto convergence theory and method, and the algorithm convergence evaluation function.This paper studied based on image processing the theory and method of automatic focus is proposed based on the convergence sorting gradient and evaluation function, this function to sort of gradient as before, calculating the gradient and, as the focus, the evaluation function experiments on target in certain functions within the scope of the size change has good performance evaluation, In order to reduce the noise on the evaluation of the sharp curve, and is proposed based on the threshold of the focus for statistical gradient algorithm is compared, and more than one in the frame of dynamic threshold, the number of gradient focus direction, the experiment results demonstrate that this method has high accuracy and good stability.In the convergence of image before HDTV do judgment is quite necessary. This paper puts forward a kind of method based on edge to a single frame of distribution gradient algorithm of image contrast judgement. Through the experiment proves this algorithm for image of equipment have good judgment performance. Based on the current image clarity, reduced the automatic focus error.This paper designs a pc-based convergence experiment system. Through the simulation of real goals and objectives of the experiment proved that this study, automatic focusing accuracy and reliability of the technology.Keywords:Digital camera; automatic focus; Evaluation function;Convergence experiment system(注意英文关键词之间要用分号隔开,这是论文的格式要求)