基于图像处理的航空成像设备自动调焦设计

Auto-Focusing Method for Airborne Image Equipment Based on Image Processing

针对当前航空成像设备中自动调焦装置结构复杂、不利于集成的问题,对基于图像处理的自动调焦方法在航空成像设备中的应用进行了研究。根据自然图像斜边缘多于水平和垂直边缘的特点,提出了基于图像斜边缘检测的对焦评价算子(Lean算子)。通过对多种对焦评价算子进行试验比较,分别选取斜边缘检测算子和卷积算子作为调焦粗搜索和精搜索阶段的对焦评价算子。针对航空成像设备光学系统的特点,提出了局部全局搜索算法(LFS)和变步长的爬山搜索算法(CHS),使用调焦行程为130步,焦深为2步的变焦镜头,分别将调焦时间由全局搜索算法的43s缩短至7s和5～8s。实验结果表明:将所提出的对焦评价算子和搜索算法结合使用,能够准确实现自动聚焦,准确度达到95%以上。

The actual auto-focusing devices in airborne image equipment have the problem of complexity in design and unable to integrate.In order to solve this problem,the application of image based on auto-focusing method in airborne image equipment was presented.Accor-ding to that the gradient edges in normal images are more than horizontal and vertical edges,a new focus measure method （Lean operator） derived from gradient edge detection was proposed.Series of experiments were committed to have the Lean method compared with the other several kinds of auto-focusing method.According to the experiment results,the Lean operator and correlation operator were respectively chosen as the focus measure method of coarse search and fine search.Then,local full search （LFS） strategy and change step hill-climb search （CHS） strategy were proposed in allusion to the feature of focus measure function of airborne image equipment.When using a lens of 130 steps focus length and 2 steps focus depth,the LFS and CHS search strategy can respectively cut the total focus time from the full search＇s 43 s to 7 s and 5~8 s.The results show that the correlation operator with the cooperation of the lean operator can locate the prime focus position accurately,the accuracy is over 95%.