A rock thin section analysis system based on continuous extinction characteristics

doi:10.13745/j.esf.sf.2020.6.36

Abstract

Abstract:

Continuous extinction refers to a phenomenon whereby the observed extinction intensity of a rotating rock thin section changes continuously under polarizing microscope observation. As an important reference for thin section identification, the extracted characteristics of continuous extinction can be used in the automatic thin section analysis. Combining digital image processing technology and clustering algorithm, we developed a thin section analysis system for grain segmentation, grain identification and quantitative data analysis. How to precisely extract the characteristics of continuous extinction—based on the extinction characteristics of minerals—became the vital part of grain identification. Therefore, we set up the control groups for extinction position alignment and baseline correction during the extraction operation. The resulting angular domain sequence images of sedimentary rock thin section under crossed polarizer show that the extinction position alignment and baseline correction contributed to more accurate continuous extinction characteristics, and the results of thin section analysis by our method matched those by expert evaluation.

Key words: crossed polarization, continuous extinction characteristics, grain identification, porosity, grain segmentation

CLC Number:

P585.1

HU Xiaoqing, GAO Shichen, ZHANG Xin, WANG Wei, ZHONG Hongru, ZHOU Heng. A rock thin section analysis system based on continuous extinction characteristics[J]. Earth Science Frontiers, 2021, 28(2): 296-304.

Figures/Tables 11

Fig.1 Extinction changes as sample table rotates from 0° to 90°

Fig.2 The rock thin section analysis system

Table 1 Formula for calculating grain morphological characteristics

特征类型	计算公式
矩形主轴比	Box(X/Y)=Box(X)/Box(Y)
圆度	roundness= $4 π S 1$ /P₁
凸度	c=S₁/S₂
粗糙度	r=(P₁/P₂)²

Table 1 Formula for calculating grain morphological characteristics

特征类型	计算公式
矩形主轴比	Box(X/Y)=Box(X)/Box(Y)
圆度	roundness= $4 π S 1$ /P₁
凸度	c=S₁/S₂
粗糙度	r=(P₁/P₂)²

Fig.3 Changes of sequence images in the process of obtaining continuous extinction characteristics. (a) Original sequence images; (b) After extinction position alignment; (c) After further baseline correction.

Fig.4 Extinction changes in different types of grains and pores

Fig.5 Results of edge fusion (a) and grain segmentation (b)

Fig.6 Characterization of representative grain morphologies

Table 2 Grain morphological parameters

编号	X/Y	roundness	c	r
a	1.9	0.6	0.8	2.1
b	1.6	0.6	0.9	2.1
c	2.1	0.7	0.9	1.4
d	2.1	0.5	0.8	3.8
e	1.2	0.7	0.9	1.8
f	1.1	0.7	0.9	1.5
g	1.2	0.6	0.9	2.2
h	1.5	0.6	0.9	2.2

Fig.7 Grain clustering (a) and segmentation (b) of image sequence and RGB distribution of each grain category (c)

Fig.8 Grain categorization results (a,b,c) and grid intersection reference image (d)

Table 3 Comparison of quantitative results of grain categorization by different methods

实验方法	比例/%
实验方法	石英	长石	溶蚀长石	火山碎屑	孔隙
直接聚类	30.06	17.95	13.30	13.20	25.43
仅消光位对齐	23.16	33.10	8.27	9.98	25.43
本文系统	25.33	32.69	11.62	4.90	25.43
网格交点	26.43	32.17	12.40	5.10	24.26

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