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调焦评价函数对离焦图像的灵敏度直接影响着自动调焦的精度。许多对调焦函数性能研究中,都只是对各个不同函数的灵敏度相互比较,忽略了调焦评价函数的灵敏度不仅和函数本身有关,还和调焦选择区域大小以及图像的空间频率等参量有关的问题。从成像原理基本公式推导出调焦评价函数灵敏度的数学模型。然后根据公式得出在光学系统的焦点附近,调焦评价函数的灵敏度与图像的空间频率成高次正比关系,与调焦区域的面积成线性正比关系,与照明光源的波长和光学系统空间截止频率成二次反比关系。最后实验证明理论分析的正确性。从而为实践中的自动调焦系统设计提供理论指导,以便有目的地选择和控制调焦系统的各个参量进一步提高自动调焦精度。
The sensitivity of the focusing evaluation function to the out-of-focus image directly affects the accuracy of auto-focusing. Many studies on the performance of the focusing function only compare the sensitivities of different functions to each other. Ignoring the sensitivity of the focusing evaluation function, it is not only related to the function itself but also to the size of the focusing selection region and the spatial frequency of the image problem. The mathematical model of the sensitivity of the focusing evaluation function is deduced from the basic principle of imaging principle. Then according to the formula, it is found that the sensitivity of the focusing evaluation function has a high order of positive correlation with the spatial frequency of the image near the focal point of the optical system, has a linear and proportional relationship with the area of the focusing area, and is close to the wavelength of the illumination light source and the optical system space The frequency is inversely proportional to the second. The final experiment proves the correctness of theoretical analysis. Thus providing theoretical guidance for the practical autofocus system design so as to purposefully select and control each parameter of the focusing system to further improve the autofocus precision.