聚焦评价函数的设计与选取是显微镜自动聚焦的核心问题之一,光照变化引起函数曲线失去理想特性, 传统的聚焦评价函数无法克服这一问题。为了解决此问题, 提出一种结合频域离散余弦变换(DCT)零系数和空域局部标准差的自动聚焦算法。通过计算图像子块的DCT高频零系数个数和局部标准差, 利用两者相反的作用效果进行除法运算, 并采用平方运算加大该算法的清晰度比率, 在不同光照条件下, 与几种传统的聚焦评价函数进行聚焦对比实验, 验证了该算法的适用性, 并对聚焦评价函数使用定量指标进行性能评估。结果表明, 该算法在低照度的条件下还能保持良好的曲线特性, 并且具有较强的抗噪性、灵敏度和稳定性。

The design and selection of focusing evaluation function was one of the key problems of automatic focusing microscopes. The illumination change would cause function curve to lose its ideal characteristics. The traditional focusing evaluation function can not overcome this problem. In order to solve the problem, an automatic focusing algorithm combining discrete cosine transform (DCT) coefficient of zero of frequency domain and local standard deviation of spatial domain was proposed. DCT coefficient of zero and local standard deviation of sub-blocks were calculated. Division operation was performed by taking advantage of the opposite effect. And square algorithm was used to increase the clarity ratio of the algorithm. Under different light conditions, compared with several traditional focusing evaluation functions, the focusing experiment was carried out to verify the applicability of the new algorithm. The performance of focus evaluation function was evaluated quantitatively. The results show that the algorithm can keep good curve characteristics under low illumination conditions and has strong anti-noise ability, sensitivity and stability.