基于简化对焦模型的自动对焦窗口调整方法

Autofocus Window Adjustment Based on Simplified Focus Model

提出一种基于简化对焦模型的自动对焦窗口调整方法用于数码相机自动对焦过程.根据初始对焦窗口和初始像距计算初始对焦窗口边界的视场角,镜头位置改变后,再根据此视场角和新的像距计算新的对焦窗口边界,进而调整对焦窗口,实现景物跟随.实验结果表明,该方法能够在物距未知的情况下近似地计算出目标的像高,与固定对焦窗口相比,能够避免背景信息的干扰,使评价函数具有单峰性.且该方法计算过程与图像内容无关,不受图像模糊程度的影响.

A method for window adjustment based on simplified focus model was proposed, which can be used in autofocus process of digital camera. Firstly, the field angles of initial focus window boundary points were calculated with initial positions of those points and initial image distance. After the lens moved, the field angles and new image distance were used to calculate the new positions of focus window boundary points. Thus the focus window was adjusted to follow the target. Experimental results show that the proposed method can estimate the drift caused by imaging magnification changing on condition that the object distance is unknown. Compared with stationary focus window, the proposed method can avoid interference of background information, thus making the evaluation function unimodal. Besides, the proposed method is independent of the defocus blur for its calculation process has nothing to do with the image content itself.