先大津法计算全局图像的阈值，再用阈值分割找出肺实质区域，再填补肺实质空洞，实现用边界追踪检测肺实质边界的目的(The calculation of the overall image threshold Otsu threshold segmentation first, and then find out the lung parenchyma, and pulmonary parenchyma fill holes, trace detection boundary in the purpo