选取适合角膜地形图仪的调焦函数并设计搜索方法。基于角膜地形图仪的图像拍摄要求及调焦系统原理,采用八种调焦评价函数对实验图像进行处理,对比分析不同调焦函数的单峰性、一致性、灵敏度、计算速度等指标。结果显示:除了Variance函数的单峰性较差,其他七种函数都有良好的单峰性、一致性和计算速度,而Laplacian函数灵敏度最高,有效测量范围小,适合精确调焦;NRSS函数灵敏度低,有效测量范围大,适合粗调焦。基于所选取的调焦评价函数,针对角膜地形图仪调焦系统,设计了一种基于阈值判别条件的搜索方法,确定其调焦阈值,并通过实验验证该方案的有效性。

The appropriate focusing criterion function for corneal topography is confirmed, and a searching method is designed. Several experimental images are processed with the eight kinds of focusing criterion functions, which are selected based on the image shooting request and the focusing system principles of corneal topography. The parameters of unimodality, consistency, sensitivity and calculating speed are comparatively analyzed through the experiment. The research results show that, all the functions have agreeable consistency and calculating speed. However, the unimodality of Variance function is unacceptable. Laplacian function owns the highest sensitivity and a shorter measuring range, which is suitable for fine tuning, NRSS funtion owns the lowest sensitivity and a longer measuring range, suitable for coarse tuning. A searching method based on threshold criterion has been designed for the focusing system of corneal topography. The threshold has been identified by the selected focusing criterion function and validated by the experiment.