介绍了基于数字图像处理方法测量透镜焦距的玻罗板分划线快速自动甄别法。该图像处理方法鲁棒性好，采用Canny法进行分划线边缘检测。用重心法计算所有线条的重心，从重心往两边搜索线条，判断选取间隔大的刻划线对，可以提高测量精度。实验数据表明该方法的相对测量不确定度能达到8．5×10^－4。为实现以数字图象处理为基础的焦距客观测量提供了一种可行的技术途径。

An image processing method used to Porro reticle discrimination in measuring the focal length of lens is introduced. It is based on the method of CCD digital image processing. The Canny edge detection method is used to identify the reticle image,and then the centroids of all lines are calculated. The line pairs with the largest space interval is searched and selected to get a high accuracy of focal length measurement with small relative standard deviation. The precision of the results is analyzed and validated. Good robustness and measurement uncertainty of 8.5×10^－4 are showed. It provides a feasible approach to realize the objective measurement of the focal length of lens based on image processing.