Determining an in-focus position of a lens

摘要

An in-focus lens position may be determined by computing a focus metric value, by counting the number of transition pixels for images of a target captured at different lens positions. Using as little as two frames to compute two focus metric values, a reasonable approximation of the in-focus lens position may be obtained. The approximation of the in-focus lens position may then be used as a starting point for a fine focus search process, to determine an in-focus lens position. An advantage here is that the focus metric values relate to the number of transition pixels and are easy to compute, and yield a reasonable approximation of the in-focus position with just a few frames. Other embodiments are also described.

主权项

1. A method for determining an approximation of an in-focus position of a lens comprising:
a) computing a statistical measure of a dark region of a digital image and a statistical measure of a light region of the digital image wherein the digital image is an image of an object captured by an imaging system using a lens; b) counting the number of transition pixels in a middle region of the digital image; c) using the number of transition pixels to obtain a focus metric value; repeating (a), (b), and (c) for an image captured at a different position of the lens to obtain another focus metric value; computing a gradient as a function of (i) the two focus metric values and (ii) the distance between their lens positions; and computing a first approximation lens focus position using the gradient.