Application of Edge Confidence Detection in the Auto-focus under Fundus Camera

Auto focus is an important technique to improve the automation for fund us camera. Selection of image sharpness evaluation function is a key to auto-focus technique. In order to ensure the focusing accuracy, a new auto-focus algorithm is proposed. It uses the definition of retinal vessel edge as sharpness evaluation function and combines the rough search with the fine search together. The retinal vessel edge can be extracted fast and accurately by the edge confidence detection, and the result is used as the evaluation function of the auto-focus. And in order to decrease the computation complexity, the proposed sharpness evaluation function is used only in the in-focus area. Experimental results show that the approach has the better unbiased ness than the traditional gradient-based evaluation function, much more advantages in focus accuracy and excellent robustness against noise.