ADAPTIVE LENS STEP CONTROL WITH MULTIPLE FILTERS FOR CAMERA FAST AUTO FOCUS

An apparatus and method for efficiently determining a final camera lens position that captures a focused input image are described. An image signal processing system of a camera capable of performing automatic focus includes a camera lens, an image sensor, a focus engine, and a lens controller. Rather than generate a single contrast value based on digital signals corresponding to a single image, the focus engine uses at least two value generators to generate multiple contrast values. The value generators are bandpass filters with different bandwidths from one another. The focus engine uses the multiple contrast values, rather than from a single contrast value, to determine a search direction for finding a final lens position of the camera lens, when to use relatively large or coarse step sizes for updating the lens position, and when to use relatively small or fine step sizes for updating the lens position.