The murals of the Tang Tomb are important materials for studying the social life of the Tang Dynasty, which have important protection and research value. In order to protect the tomb murals as longer as possible, it is necessary to restore the murals and accurately record the restore location. Nevertheless,the restored murals are difficult to observe directly the restore area through the human eye. This paper proposes a method to reveal the restored areas, by extracting the main components of the Multi-Hyper-spectral image of the mural with the Minimum Noise Fraction (MNF) Rotation, and the location of the restored area is clearly observed from the main component. In addition, the mural sketch reflects the main content of the mural of the Tang Tomb murals, which are of great significance to the restoration and protection of the Tang Tomb murals. In this paper, we also proposed a new method to extract the sketch of Tang Tomb mural. For the bands sensitive to the composition of the sketches, the sparsely constrained sparse non-negative matrix under- approximation method is used to decompose the optimal sketches composition, and then the sketches are automatically extracted based on the idea of layer superposition. Through the experiments on the mural paintings in the three tombs, the results demonstrated that the proposed method could effectively perceive the area of mural restoration and automatically extract the sketch accurately and clearly, while saving manpower.
Pulsed terahertz reflected imaging technology has been expected to have great potential for the non-invasive analysis of artworks. In this paper, three types of defects hidden in the plaster used to simulate the cases of defects in the murals, have been investigated by a pulsed terahertz reflected imaging system. These preset defects include a circular groove, a cross-shaped slit and a piece of “Y-type” metal plate built in the plaster. With the terahertz reflective tomography, information about defects has been determined involving the thickness from the surface of sample to the built-in defect, the profile and distribution of the defect. Additionally, three-dimensional analyses have been performed in order to reveal the internal structure of defects. Terahertz reflective imaging can be applied to the defect investigation of the murals.
Terahertz time-domain spectroscopy (THz-TDS) imaging technology has been proposed to be used in the non-invasive detection of murals. THz-TDS images provide structural data of the sample that cannot be obtained with other complementary techniques. In this paper, two types of defects hidden in the plaster used to simulate the cases of defects in the murals, have been investigated by the terahertz reflected time domain spectroscopy imaging system. These preset defects include a leaf slice and a slit built in the plaster. With the terahertz reflective tomography, information about defects has been determined involving the thickness from the surface of sample to the built-in defect, the profile and distribution of the defect. With this THz tomography, different defects with the changes of optical thickness and their relative refractive index have been identified. The application of reflective pulsed terahertz imaging has been extended to the defect detection of the murals.