In order to remove the effect of the changes of atmospheric pressure and temperature on the image definition of aerial CCD camera and ruduce control sectors, an autofocusing system of locating focal plane position based on two kinds of image definition criterion function was designed. Gray difference function was used for coarse adjustment with big step in wider range and Brenner function was used for fine adjustment with small step in narrow range. The procedure of autofocusing was to get the maximum of the image definition criterion function by employing the hill-climbing algorithm. The combination of coarse and fine adjustment can not only reduce the time for data processing, but also enhance the focusing accuracy. The conclusion of the optical measurement and flight indicated that the system runs steadily and has an accuracy of 0.01 ran, which can meet the requirements of the focal plane position accuracy of aerial camera.%为消除大气压力和温度的变化对航空CCD相机成像清晰度的影响,减少相机控制环节,设计了一种基于两种图像清晰度评价函数确定镜头焦面位置的自动检焦系统.灰度差分法函数用于较大范围大步长粗检焦,Brenner函数用于小范围小步长细检焦,检焦过程运用爬山搜索法求取评价函数的最大值.这种采用粗精结合的控制方法不仅有效地节省了图像处理的时间,而且提高了检焦的精度.经过光学测试和试验证明,该系统运行稳定,检焦精度为0.01 mm,满足了航空相机焦面位置精度要求.
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