Improved Auto-Focus Search Algorithms for CMOS Image-Sensing Module
Digital image capturing devices currently available in the market include camera phone, webcam, and vehicle rear-view camera. With the advancement in lens module manufacturing technologies, efforts have been made to improve the image quality, diversify the product functions, and reduce the product size. Facing the large market demands, it is important to achieve higher lens module output in mass production. Under this trend, the process of focusing the large quantity of lenses efficiently is an issue to be concerned. The conventional active auto- focusing (AF) technology relies on distance measuring equipment to measure and adjust the relative distance between the object and the lens. Whereas, passive AF technology does not require any distance measuring equipment; instead, it em ploys digital images acquired by the lens to calculate the sharpness of the image, which serves the basis for changing the lens focus, and searching for the imaging position with a focus value that has reached the threshold. The most important condition for AF algorithm is the real-time feature; however, it is time-consuming for regular search algorithms to solve the focusing problem. To solve this issue, this research proposes to integrate the intelligent fuzzy control theory and the fuzzy sliding-mode controller, which is characterized by its sliding surface, to build an AF system controller. The controller can control the rotary angle of the motor that drives the lens movement, in order to achieve CM OS image-sensing module AF quickly.
auto-focus cmos fuzzy control theory fuzzy sliding-mode controller sliding surface