航空红外相机自动调焦设计

Design of automatic focusing for aerial infrared imaging camera

为克服恶劣复杂的航空环境给系统带来的失焦现象,系统中引入自动调焦模块。通过采集、分析不同程度失焦的中波红外图像序列,对空域内几种调焦评价函数的灵敏度、无偏性、稳定性、计算速度等指标进行测试和验证,最终得到适合于红外成像自动调焦系统的调焦评价函数。为了提高该调焦评价函数的信噪比,提出了一种基于图像预处理的信噪比改善算法,保证函数在正焦面两侧呈单调性。最终制定出粗细结合的快速爬山搜索策略,先以大步距进行粗略调焦缩短时间,再用低于半倍焦深的小歩距精细调焦保证精度。基于640×512中波制冷探测器,搭建了一个焦距为300 mm、F/2的卡塞格伦折反式红外光学系统。试验结果表明该自动调焦模块可以保证实时性和准确性,满足具有较大噪声的红外成像系统的需要。

In order to overcome the out-of-focus phenomenon caused by the harsh and complex aeronautical environ-ment, the automatic focus module was introduced in the system. Mid-wave infrared image sequences in different out-of-focus were collected and analyzed on the test platform, and then the parameters of sensitivity, consistency, stability and calculating speed of some focusing evaluation functions in spatial domain were tested and validated to find the suitable function for this infrared imaging system through experiments. In order to improve the SNR of the focusing evaluation function, a method based on image preprocessing is proposed to ensure the function,s monotonic property. And then, a climbing search strategy of rapid auto-focusing combining rough focusing and fine focusing was formulated. Firstly,the function was used to roughly focus with large step to shorten the time and then it was used to finely focus in a narrow step to ensure accuracy. Based on mid-wave 640 ×512 focal plane array cooled detector, the Cassegrain catadioptric optical system with focal length 300 mm,F/2 was set up. The design has been realized on the auto-focusing hardware platform of the infrared imaging. By experimental verification, the auto-focusing function module can ensure real-time and precision, and meet the infrared imaging system requirement with large noise.