该改进算法在预处理阶段对图像进行平滑操作并设置适当的梯度阈值，即减少了梯度图像中非重要区域的产生。
In the improved algorithm, the pre-processed image is smoothed and the proper gradient threshold is set to prevent the generation of insignificant regions.
ROI提取方法计算人耳大小区域的梯度均值，通过设定合适的阈值得到较少的候选区域。
The mean value of gradient magnitude in the regions, of which size is equal to ear, is computed by the extracting ROI method.
测试了晶体的光折变阈值、双折射梯度和消光比。
The optical refraction threshold. birefringent gradient and extinction ratio were measured.
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