Modified fast climbing search auto-focus algorithm with adaptive step size searching technique for digital camera

A practical real-time auto-focus algorithm for digital camera ispresented. and it improves the reliability and speed of auto-focus process, especially suitable for mega-pixel high definition camera. The proposed algorithm adopts threshold gradient and edge point count technique besides focus value function, instead of traditional two-stage climbing search algorithm that uses focus value function only. Additionally, a relative difference ratio circuit is also proposed, which can implement adaptive step size searching to increase the searching speed. By adopting the modified algorithm on the protoiype of our mega-pixel digital camera, real-time auto-focus function is verified. The proposed algorithm is implemented in test camera chip that has been manufactured in 0.25um CMOS digital process. Index Terms modified fast climbing search, focus value, threshold gradient, edge point, adaptive step size searching, relative difference ratio.