Study on the parameterized hollow boundary identification method based on infrared thermal imaging

The problem of hollowing threatens the integrity of cultural relics. Infrared thermography provides a basis for identifying hollows but struggles to accurately determine their boundaries. Existing methods predominantly rely on conventional thermographic parameters and lack systematic studies on the extraction and analysis of thermally sensitive features of hollows under complex field conditions. In particular, research on the precise detection of hollow boundaries in rock art remains limited. Based on the theory of heat transfer, this paper constructs a distribution model of the temperature field in the hollow region, quantifying the dynamic characteristics of heat diffusion in the hollow area. A new method for calculating the hollow radius based on infrared thermography is proposed, and a correlation analysis of the unknown parameter β in this method is conducted using numerical simulation. Based on the analysis results, a quantitative relationship between the parameter β, ω and R is established. To test the accuracy of the computational method under complex surface conditions, calculations were performed on 200 measurement points with different hollow radii, among which 73 % of the points had a relative error of less than 14 %. The experiment also conducted a comprehensive analysis of the error performance of different methods from the perspectives of time and hollow size. The experiment also analyzed the error performance of different methods. This analysis considered both the time dimension and the size of the hollow areas. The experiment also conducted a comprehensive analysis of the error performance of different methods from the time and hollow size dimensions. The results show that the method in this paper achieves an average relative error rate of 9.89 % and a standard deviation of 0.22, compared to 16.69–24.82 % and 0.32–0.42 respectively in existing methods, demonstrating clear advantages in accuracy and stability, demonstrating the smallest fluctuation and the best stability compared to other methods. This method was also applied to on-site hollow detection in the Damaidi rock paintings. Its performance was compared with the on-site hardness testing method. Both methods gave similar results in identifying hollow boundaries. This further confirms the reliability and applicability of the proposed method.