Auto Focus Using Adaptive Step Size Search and Zoom Tracking Algorithm

In this paper, an adaptive step size auto focus search algorithm and a reduced zoom tracking algorithm are proposed. Many different auto focus search algorithms exist, such as global search, binary search, Fibonacci search, and so on. Global search can ensure the global peak is found correctly, but the search time is too long. The search time of binary or Fibonacci search is shortened, but the lens has to move back and forth frequently, which is prone to have step errors. Our adaptive step size search algorithm performs only one backward movement while the search time is greatly decreased. Zoom tracking is to adjust a camera’s focal length continuously, to keep the in-focus state of an image during zoom operation. A simple table-lookup with interpolation method is commonly used, but the size of the table is important. Our reduced zoom tracking algorithm reduces the table size while still achieving good image quality.