In the investigation, protection and restoration of murals, the exact location and size of fragmentation disease can be labeled to facilitate the subsequent protection and cultural heritage of murals. However, manual labeling is time-consuming and laborious, and the results will be various due to the different experience of experts, which is not conducive to the promotion of intelligent cultural relic protection and restoration. The intelligent labeling of mural diseases through artificial intelligence can greatly improve the efficiency of mural restoration and solve these deficiencies. Therefore, an intelligent labeling method for mural fragments based on gradient-trainable Gabor and U-Net is proposed. In this paper, the disease labeling problem is transformed into the image segmentation problem for disease regions. However, due to the rich texture of the mural image and the complex edges of the fragmentation regions, a lot of detail is lost for disease labeling directly using the U-Net network. Different from previous studies, this method uses gradient-trained Gabor in the encoders to extract texture features of fragmentation disease and obtain more texture information of the disease region. In particular, res2convolution is embedded into the skip connections to narrow the semantic gap between encoder and decoder and better inject the texture information of fragmentation disease into the deep network. Finally, we proved that the method proposed in this paper can realize the intelligent labeling of fragmentation diseases accurately and efficiently through the murals of Han Tomb at Xi 'an Jiaotong University.
The sketches of painted cultural objects can be the most indicative of the style of paintings. Extraction of the sketches is an integral process used by conservators and art historians for documentation and for artists to learn historical painting styles through copying and painting. However, at present, sketch extraction is mainly manually drawn, which is not only time-consuming, but also subjective and dependent on experience. Therefore, both accuracy and efficiency need to be improved. In recent years, with the development of machine learning, a series of extraction methods based on edge detection have emerged. However, most of the existing methods can only perform successful extraction if the sketches are well preserved , but for the data with faded sketches or severe conservation issues, the extraction methods need to be improved. It is beneficial to extract the bands that accentuate the sketches while suppressing the effects of the degraded areas and the overlapping paints. We propose a sketch extraction method based on hyperspectral image and deep learning. Firstly, the hyperspectral image data is collected and the bands sensitive to the sketches are extracted by a prior knowledge of the sketches (e.g. near infrared bands will be chosen if the sketches are made of carbon ink), and a dataset including a large number of existing natural images is used to pre-train the bi-directional cascade network (BDCN). The network parameters in the model are then fine-tuned by using the images of painted cultural objects drawn by experts, so as to solve the problem of insufficient sketch dataset of painted cultural objects and enhance the generalization ability of the model. Finally, the U-net network is used to further suppress the noise, i.e. unwanted information, and make the sketch clearer. The experimental results show that the proposed method can not only effectively extract sketch from ideal data, but also extract clear sketches from data with faded sketches and even with noise interference. It is superior to the other six advanced based on edge detection methods in visual and objective comparison, and has a good application prospect. The proposed deep learning method is also compared with an unsupervised clustering method using Self-Organising Map (SOM) which is a ‘shallow learning’ method where pixels of similar spectra are grouped into clusters without the need for data labeling by experts.
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.
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