Threshold segmentation method of CT scanning data of coal and rock samples considering beam hardening effect and its application
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摘要: 射束硬化是工业CT应用中的常见现象，射束硬化会导致同一密度组分呈现不同的灰度值，严重影响对各组分的分割及后期重构。为对射束硬化效应影响下的煤岩试样CT扫描数据精确划分，研究了射束硬化影响下的煤岩试样灰度值的分布规律，发现灰度束上灰度值的变化能够真实反映组分密度变化，并从理论上推导证明了这一结论，据此提出了灰度束阈值分割方法。灰度束阈值分割方法是将CT重建后的三维灰度数据体离散为一维的灰度束，根据目标组分种类的数量选择合适的全阈分割方法进行分割，并对其进行多值化，将多值化后的一维数据体重新集合为三维数据，三维数据中不同值代表不同组分，从而将各组分区分。采用灰度束阈值分割方法对6种射束影响下的煤岩组合体扫描数据进行了阈值分割并重构，证明了本方法的有效性。研究结果能够对非均质煤岩及其他材料CT扫描数据精确划分提供参考。Abstract: Beam hardening is a common phenomenon in the application of industrial computerized tomography (ICT). It can cause different grayscale values in components with the same density, which affects the threshold segmentation and later reconstruction of components seriously. Herein, study was conducted on the distribution law of grayscale values under the effect of beam hardening, so as to segment the CT scanning data of coal and rock samples under the beam hardening effect accurately. Through the study, it is found that the change in grayscale value on the grayscale beam could truly reflect the change in component density, which is proved by theoretical derivation. Based on this, the threshold segmentation method was proposed for the grayscale beam. Specifically, the threshold segmentation method of grayscale beam is to discrete the three-dimensional grayscale data volumes through CT reconstruction as one-dimensional grayscale beams at first, then segment and multivalue them with the appropriate full-threshold segmentation method according to the number of target component types, and finally gather the multivalued one-dimensional data volume for three-dimensional data. Thereby, the components can be distinguished through the different values in the three-dimensional data that represent different components. Herein, the threshold segmentation method of grayscale beam was used to segment and reconstruct the scanning data of coal-rock combination under the effect of 6 beams, with the validity of this method verified. The research results could provide a reference for the accurate segmentation of CT scanning data of non-homogeneous coal, rock and other materials.
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Key words:
- ICT /
- beam hardening /
- threshold segmentation /
- coal and rock combination /
- grayscale beam
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图 1 单能及多能射线投影值与射线穿过厚度关系
Fig. 1 Relationship of the projection value of mono-energy and multi-energy rays with the penetration thickness
图 5 理想状态及射束硬化影响下煤岩水平灰度分布
Fig. 5 Horizontal grayscale distribution of coal and rock in ideal state and under beam hardening effect
图 6 纵切面垂向中线灰度分布及频率
Fig. 6 Grayscale distribution and frequency of vertical centerline in longitudinal section
图 7 试件1纵切面不同位置垂向中线灰度分布
Fig. 7 Grayscale distribution of vertical centerline at different positions in longitudinal section of specimen 1
图 8 扫描角度α时试件中各点相对位置
Fig. 8 Relative position of each point in the sample at scanning angle α
图 13 灰度束阈值分割法二值化效果
Fig. 13 Binarization of threshold segmentation method of grayscale beam
表 1 煤岩不同位置处灰度值
Table 1 Grayscale value at different locations of coal and rock
试件编号 0 mm边界灰度值 50 mm边界灰度值 最小灰度值 硬化系数 岩体部分 试件1 255 255 125 2.04 试件2 255 255 111 2.3 试件3 252 251 119 2.12 试件4 255 225 89 2.87 试件5 255 255 119 2.14 试件6 255 255 91 2.80 煤体部分 试件1 99 96 66 1.50 试件2 101 90 65 1.55 试件3 121 118 87 1.39 试件4 121 118 79 1.53 试件5 108 108 78 1.38 试件6 131 181 44 4.11 
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