A Real-time Continuous Automatic Focus Algorithm for Digital Cameras

Most conventional continuous auto-focus algorithms appearing in the literature fail to address how to focus on a desired near object when there are multiple objects in the scene, especially in the presence of a high contrast background. The stability and responsiveness of these methods also hinge on hard-to-set thresholds. In this paper, a multiple-window, rule-based, continuous auto-focus method is presented which is capable of focusing on a desired object and deploys easy-to-set thresholds which control stability and responsiveness. This method has been implemented for real-time use on the Texas Instruments Digital Camera Development System powered by the DM320 media processor. Experimental results show that the method provides stable and responsive focusing suitable for both live preview and movie modes of digital still/video cameras