煤体 CT 图像阈值分割是其三维真实结构重构的前提.基于单轴压缩状态下煤体的 CT 图像,提出了一种基于图像灰度分布的孔隙度计算方法,结合灰度直方图,利用实测孔隙度反推法对煤体CT图像进行了裂隙--煤基质--煤杂质三值化,同时与最大类间方差法和最大熵法的三值化结果进行了对比分析.结果表明,最大熵法对于煤基质和煤杂质不能较好区分;最大类间方差法对于图像微小区域灰度的突变 (裂隙的产生) 敏感性低,无法有效区分裂隙与煤基质;本文改进的灰度直方图法避免了最大类间方差法和最大熵法的劣势,具有较好的图像三值化效果,且煤基质与煤杂质间的阈值基于实验结果得到,具有更高的可信度和准确度.%The threshold segmentation of CT image of coal is the prerequisite for the reconstruction of 3D real structure. A porosity calculating method was proposed based on grey level distribution of CT images obtained under uniaxial compression. Combined with the gray scale histogram, CT images were experienced three-value-segmentation of fracture, coal matrix and inclusion by inverse process from experimental porosity. The three-value-segmentation results obtained by Otsu method, maximum entropy method and the improved gray histogram method show that maximum entropy method can not get a good segmentation between coal inclusion and coal matrix,and Otsu method can not effectively split crack and coal matrix for its low sensitivity to dramatic variation for gray value in small area of the image. However,the improved gray histogram method eliminates the disadvantages of the two methods mentioned above. The threshold of coal matrix and inclusion is obtained with higher reliability and accuracy based on the experimental results, and a better three-value-segmentation of image is obtained by the improved grey histogram method.
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