摘要十字线目标作为调焦系统中的常见目标,其调焦精度是影响调焦系统测量结果的关键因素。传统的调焦函数在灵敏度和实时性方面不能完全满足自动调焦要求。基于调制传递函数(modulation transfer function,MTF)的自动调焦算法通过连续测量多幅图像在固定频率下的MTF值绘制调焦曲线,得到调焦曲线的唯一极值点即正焦位置;在Matlab运行环境下,与现有算法进行比较,结果表明,基于数字图像MTF的调焦函数可实现单张图片的清晰度值计算仅用0.01s,该算法实时性更好、灵敏度更高,具有应用价值。
Abstract：The cross-line target is the common target in focusing systems. Its focusing accuracy is the key factor affecting measurement results. The traditional focusing function cant fully meet the requirements in terms of sensitivity and real-time performances. The focusing curve is drawn by continuously measuring MTF values of multiple images at fixed frequencies with the automatic focusing evaluation function based on MTF(modulation transfer function), and the focus position is gotten at the only extreme point of the focusing curve. In the Matlab environment, the result shows that the focusing function based on the MTF of the digital image can only use 0.01 s to calculate the definition value of a single image. The algorithm has the better real-time performance, higher sensitivity and application value.
［1］原育凯.光学系统的自动调焦方法［J］. 红外, 2004, (6): 15-21.
Yuan Y K. Auto-focusing Method of Optical System［J］. Infrared, 2004, (6): 15-21.
［2］张辉.CCD图像检测系统自动调焦的研究［D］. 哈尔滨: 哈尔滨工业大学, 2007.
［3］林娣, 曾志强, 王俊元, 等.弹体导带槽宽度两次视觉精确测量方法研究［J］. 计量学报, 2017, 38 (2) : 149-152.
Lin D, Zeng Z Q, Wang J Y, et al. Research of Two Vision Accurate Measuring Method of Elastomers Conduction Band Groove Width［J］. Acta Metrologica Sinica, 2017, 38(2): 149-152.
［4］赵辉, 鲍歌堂, 陶卫.图像测量中自动调焦函数的实验研究与分析［J］. 光学精密工程, 2004, 12(5): 531-536.
Zhao H, Bao G T, Tao W.Experimental Research and Analysis of Auto-Focusing Function for Image Measurement［J］. Optics and Precision Engineering, 2004, 12(5): 531-536.
［5］左勇, 束小梅, 李伟.基于视觉检测和图像处理技术的压痕直径自动测量方法研究［J］. 计量学报, 2010, 31 (z1): 148-152.
Zuo Y, Shu X M, Li W. Measuring Method of Indentation Diameter Based on the Machine Vision and the Digital Image Processing［J］. Acta Metrologica Sinica, 2010, 31 (z1): 148-152.
［6］何祯鑫, 刘春桐, 黄先祥, 等.基于MTF辅助正焦判断的自动调焦搜索算法［J］. 光子学报, 2014, 43(4): 411002-8.
He Z X, Liu C T, Huang X X, et al. Searching Algorithm of Auto-focusing Based on MTF Auxiliary Focal Judgement［J］. Acta Photonica Sinica, 2014, 43(4): 411002-8.
［7］Kehtarnavaz N, Oh H J. Development and real-time implementation of a rule-based auto-focus algorithm［J］. Real-Time Imaging, 2015, 9(3): 197-203.
［8］刘斌, 赵建章, 孔祥欣, 等.基于FPGA的高动态范围红外图像细节增强算法［J］. 计量学报, 2018, 39(4): 47- 51.
Liu B, Zhao J Z, Kong X X, et al. HDR Infrared Image Detail Enhancement Method Based on the FPGA［J］. Acta Metrologica Sinica, 2018, 39(4): 47-51.
［9］杜飞明, 文益民, 陈方.基于十字线灰度图像清晰度模型的构建与应用［J］. 计算技术与自动化, 2009, 28(3): 83-85.
Du F M, Wen Y M, Chen F.On Constructing and Applying Clarity-evaluation-model of the Cross-line Gray-scale Image［J］. Comput Technol Autom, 2009, 28(3): 83-85.
［10］孙红利, 冯旗, 董峰.图像清晰度评价算法研究［J］. 传感器与微系统, 2017, 36(2): 67-70.
Sun H L, Feng Q, Dong F. Reasearch on Algorithm for Image Clarity Evaluation［J］. Transducer and Microsystem Technologies, 2017, 36(2): 67-70.
［11］陈珊珊.基于CCD的MTF系统自动调焦系统开发及误差分析［D］. 上海:复旦大学, 2011.
［12］李飞, 刘文丽, 洪宝玉, 等. X射线成像系统调制传递函数测试方法及其评价［J］. 计量技术, 2012, (7): 20-23.
［13］于谦.光学检查镜头的MTF测试方法研究［D］. 杭州:浙江大学, 2010.
［14］马卫红.基于图像分析的光学传递函数测试技术研究［D］. 西安:中国科学院西安光学精密机械研究所, 2005.
［15］尹传祥, 高思田, 李琪, 等.计量型紫外光学显微镜自动对焦系统的研究［J］. 计量学报, 2014, 35(z1): 26-30.
Yin C X, Gao S T, Li Q, et al. Research on Auto-focusing System of Metrological Ultraviolet Optical Microscope［J］. Acta Metrologica Sinica, 2014, 35(z1): 26-30.
［16］赵梓朝, 陈启梦, 唐子博, 等. 高精度动态星模拟器的光学系统设计［J］. 计量学报, 2018, 39(5): 641-644.
Zhao Z C,Chen Q M,Tang Z B,et al. Optical System Design of High Precision Dynamic Star Simulator［J］. Acta Metrologica Sinica, 2018, 39(5): 641-644.
2020, Vol. 41 
