基于投影微分算法提出了一种应用于多光谱成像仪的自动对焦方法, 该方法结合图像处理单元和多个波段的探测器调焦辅助机构来同时实现多个波段的独立自动对焦。首先, 根据观测需要对自动对焦窗口进行手动选取, 或结合投影微分与目标边缘的对应关系进行对焦窗口的自动选择; 然后, 将参与自动对焦计算的图像的对焦窗口内的数据做x与y方向投影, 对这两个方向投影数组的微分1范数均值求均方根, 并将其作为该帧图像的清晰度评价值; 最后, 结合经典的爬山搜索算法, 完成系统的自动对焦过程。实验结果显示, 同等条件下投影微分算法与经典的Brenner、能量梯度及Roberts梯度和算法具有同样好的评价效果, 能够准确地实现系统的自动对焦, 而其算法时间分别仅为这3种算法的0.67、0.33和0.33倍。这些结果表明, 投影微分算法具有良好的单峰性与无偏性、较高的灵敏度及很好的实时性, 能够满足系统的高精度自动对焦要求。

An auto-focusing method used for the multi-spectral imagers was proposed based on differential projection. The method uses an image processing unit and auxiliary focusing equipment of sensors to implement the auto-focusing processes for different spectral bands separately and simultaneously. Firstly, the focusing window was delimited manually according to the observation needs or was searched automatically on the basis of the corresponding relations of differential projection and target edges. Then, the focusing window data of the image to be focused and calculated were projected in x-direction and y-direction, the 1st norm of the two projection arrays' first order differential values was derived and the mean of the two sets of 1st norm data was computed. Furthermore, the RMS of the two means was taken as the definition evaluation value of this image. Finally, combined with the classic mountain climb-searching method, the auto-focusing process was finished. Experimental results indicate that the auto-focusing method based on differential projection can be realized accurately, and it has the same effect with the classic Brenner, energy gradient and Roberts gradient algorithm, approximately. However, the running time of differential projection is only 0.67 times of Brenner, 0.33 times of Energy gradient, and 0.33 times of Roberts gradient. With the advantages of its strong single peak features, good unbiased characteristics, high sensitivity and excellent real-time, the method can meet the requirements of high-precision auto-focusing very well.