利用单色平行光照射玻璃微珠,入射光在玻璃微珠内经过一次或多次内反射后出射光在最小偏向角会形成彩虹条纹。基于几何光学理论,根据最小偏向角的大小计算玻璃微珠的折射率。为了实现其快速测量,采用参数递推公式计算Otsu法的最佳阈值,并用改进的Otsu法对彩虹图进行了有效的阈值分割。提出了一种能快速有效判断彩虹条纹边缘的方法,并用该方法自动测量了彩虹条纹最外环边缘半径,从而实现了最小偏向角的快速计算。此外,对玻璃微珠折射率测量过程中的不确定度进行了计算,对不同型号的玻璃微珠,折射率的不确定度在10-4数量级,验证了上述方法的正确性。

When a monochromatic parallel beam illuminates a glass bead, the emergent rays which experience one or more times internal reflection in the glass beads will form the rainbow fringes at the minimum deviation angle. In the article, on the basis of the theory of geometrical optics, the refractive index is calculated by measuring the minimum deviation angle. In order to speed up the measurement of refractive index, the optimal threshold of OTSU method is calculated using the recurrence formula, and the effective threshold segmentation of the rainbow image is determined by the improved OTSU method. Then, a fast and effective method to determine the rainbow fringe edge is proposed to measure the radius of the rainbow fringe edge automatically, and the minimum deviation angle is obtained correspondingly. In addition, the uncertainty for the glass beads refractive index measurement is calculated. The refractive indices of the different types of glass beads are measured by this method, and the uncertainty in the refractive index is about 10-4 order of magnitude. The results verify the method is correct.