## 3 Analysis of Results
### Comprehensive Assessment of the Extent of Structural Degradation of Red Sandstone
#### 3.3.3 Correlation Analysis of the Degree of Red Sandstone Degradation with CT Grayscale Images
The correlations obtained from the prediction simulations also show a strong correlation between the two feature parameters, the third-order central moment and the probability of gray level greater than 200 (Pg > 200), and the degree of degradation, and since the basic properties of each feature parameter are characterizing the image features and their nature is correlated, it can be assumed that the two feature parameters, the third-order central moment and the probability of gray level greater than 200 (Pg > 200), can directly characterize the degree of degradation of the red sandstone from the image features. From Figure 12 and the above analysis, it can be found that there is a strong correlation between the characteristic parameters of the CT grayscale image of the red sandstone and the degree of degradation, which can be used as a method to measure the degree of degradation of the red sandstone. Furthermore, there is a highly consistent pattern of change in the relationship between the third-order central moments and Pg > 200 and the degree of degradation. In the initial stage, the third-order central moments and Pg > 200 change drastically with the degradation, and as the degree of degradation increases, the rate of change in the two characteristic parameters is decreasing. \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Feature Parameters of CT**} & \multicolumn{2}{c}{**Degradation Degree**} \\ \cline{2-3}  & **True Value + \(LS\) Layer** & **Simulated Predicted** \\  & **Predicted Value** & **Values** \\ \hline Average gray level & 0.7268 & 0.7821 \\ Standard deviation & 0.7035 & 0.7620 \\ Third-order central moment & 0.7934 & 0.8409 \\ Homogeneity & 0.7024 & 0.7625 \\ Average message size & 0.7020 & 0.7599 \\ Maximum probability gray level & 0.7339 & 0.7912 \\ (Pg > 200) & 0.8581 & 0.8999 \\ \hline \hline \end{tabular} Note: A strong correlation between two factors is considered when the correlation degree > 0.8, a weak correlation between two factors when the correlation degree \(\in\) (0.5, 0.8), and no correlation between two factors when the correlation degree \(<\) 0.3.  
\end{table} 
Table 5: Calculated correlation between feature parameters and degree of degradation for CT grayscale images. However, the opposite change occurs at the fourth layer, which may be due to the poor recognition of CT images taken at this layer or the presence of other forms of damage at the fourth layer rather than a single natural erosion. In general, there is a strong correlation in the characteristic parameters of CT grayscale images of red sandstone between third-order central moments and Pg > 200 and the degree of degradation. However, this study did not establish a better model to express the correspondence between the characteristic parameters of CT grayscale images of red sandstone and its degree of degradation due to the limitation of data volume, and it did not obtain a model to measure the degree of degradation of red sandstone using the characteristic parameters of CT grayscale images. Further work will be carried out in this area.