## 4 Experimental Research
### Experimental Results and Analysis
#### 4.3.3 Multi-Scale Luminance-Enhancement Module Ablation Experiments  
To assess the individual impact of various components within the network, a series of ablation studies was performed. As shown in Figure 13, the images from left to right include the enhancement result of the low-illumination image, the corresponding high-illumination reference, the enhancement result using the base network structure, the result with the integration of the multi-scale brightness-enhancement module, the result with the incorporation of the NR-Transformer, and the final enhancement result of the complete proposed model. Quantitative comparisons for each configuration are provided in Table 3. In Figure 13, darker regions represent coal seam areas, while lighter regions correspond to rock and background areas.  
Figure 12: Comparison of experimental results of coal and rock segmentation images. Subfigures (**a–f**) show representative samples selected from the dataset, reflecting typical coal and rock interface scenarios.  
Figure 13: Comparison of the results of the ablation experiment with the image-enhancement module. Subfigures (**a–f**) present representative samples selected from the dataset to illustrate the visual differences under various experimental conditions.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Experimental Group** & **1** & **2** & **3** & **4** & **5** & **6** \\ \hline Infrastructure & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) \\ Multi-Scale & & \(\surd\) & & & & \(\surd\) \\ Brightness-Enhancement & & \(\surd\) & & & & \(\surd\) \\ Module & & & & & & \\ Pyramid Pooling Module & & & & \(\surd\) & & \\ NR-Transformer & & & \(\surd\) & & & \(\surd\) \\ Transformer & & & & & \(\surd\) & \\ PSNR & 16.087 & 18.639 & 17.478 & 17.281 & 15.357 & **21.288** \\ SSIM & 0.714 & 0.763 & 0.746 & 0.748 & 0.691 & **0.783** \\ Quantity of participants/10\({}^{6}\) & 21.46 & 21.68 & 20.92 & 21.62 & 17.06 & **21.09** \\ \hline \hline \end{tabular}
\end{table}
Table 3: Comparison of results of ablation experiments with luminance enhancement modules.  
The basic model structure without any enhancements (Group 1) produced the lowest evaluation scores, exhibiting poor image enhancement quality, noticeable distortion, and unstable brightness consistency.  
Group 2, which incorporates the multi-scale brightness-enhancement module, achieved improved evaluation metrics over Group 1 without a significant increase in parameter count or computational cost. It provided more uniform brightness and effectively avoided local overexposure and underexposure. However, the resulting image clarity was suboptimal and remained susceptible to minor noise interference.  
Group 3, which integrates the NR-Transformer structure, also outperformed Group 1. Due to the absence of convolutional layers, the overall parameter count was reduced, and the enhanced images showed fewer distortions and improved clarity. However, the illumination remained uneven.  
Group 4 replaces the multi-scale module with a pyramid pooling module. Compared to Group 2, it resulted in larger performance discrepancies despite its advantage of a smaller number of parameters.  
Group 5 utilizes the original Transformer structure. Although it further reduces the parameter count, its enhancement performance was inferior to even the baseline (Group 1), with lower evaluation scores overall.  
Group 6 combines the multi-scale brightness-enhancement module (Group 2) and the NR-Transformer (Group 3). This configuration achieved the best overall evaluation metrics, along with reduced parameters and improved computational efficiency. The enhanced images were closest in appearance to the high-illumination ground truth, demonstrating minimal distortion, uniform lighting, and a light distribution that closely resembled natural illumination, resulting in satisfactory image-enhancement outcomes.