Automatic Focusing Apparatus and Method for Digital Images Using Automatic Filter Switching

摘要

An apparatus and method for automatically focusing a lens of a digital imaging device, such as a digital still or video camera or camera phone, that reduces the auto focus time while not compromising image sharpness quality and simultaneously reducing device power consumption due to focus actuator movement, all without tuning or adjustment of thresholds or parameters is disclosed. The present invention automatically computes a set of digital band-pass filters matched to the imaging device specifications along with corresponding step-size magnitudes. A filter-switching search for the in-focus focus actuator position is formulated such that filters are switched and step-sizes are reduced as the search gets closer to the in-focus position by utilizing local estimates of the first and second-order differential information of the focus value surface.