A fast auto-focusing technique for multi-objective situation

An image based passive auto-focusing algorithm for the multi-objective situation is proposed. The algorithm is composed of the image sharpness measure and the search strategy. To achieve real time requirements, an effective and efficient image sharpness calculation based on Sobel operator is proposed. And a weighted gradient histogram based threshold selection method is used to reduce the influence of background noises. During the multi-objective search, several objects in the scene will lead to multiple peaks on the image sharpness curve. In this paper, a near-object priority search method is presented to search the real peak. The method will drive the lens focus on the nearest object automatically by detecting sharpness changes in the sub-windows. Finally, the results of experiments on several video sequences show that the presented algorithm has better performance on speed and accuracy in the multi-objective focus.