Restoration of an ancient temple mural by a local search algorithm of an adaptive sample block

Abstract

Long-term influences in the external environment, including light, temperature and humidity, have caused varying degrees of damage to ancient Chinese murals. Allowing people to appreciate the original style of the murals has become important to experts, and the development of image processing and machine learning technology has allowed intelligent restoration of ancient murals. This paper proposed the adaptive sample block and local search (ASB–LS) algorithm based on the Criminisi algorithm to address the flaking deterioration of Kaihua Temple murals from the Song Dynasty. ASB–LS achieved virtual restoration of damaged areas. First, the mural’s compositional characteristics were analyzed, the structure tensor was introduced, and the data items were redefined using eigenvalues to ensure accurate transmission of the image’s structural information. Then, the data item was used to form a new priority function to improve the image filling order. Finally, the sample block size was adaptively selected by the average correlation of the structure tensor, and a local search strategy was used to improve matching efficiency, which effectively avoided mispropagation of the restored image structure and blinded search of the matching block. Experiments were performed on the Song Dynasty murals in the Kaihua Temple for two types of deterioration: flaking deterioration and artificial destruction. Compared with the Criminisi algorithm and two improved algorithms, the proposed ASB–LS algorithm had better subjective analysis and objective evaluation. Subjective visuals significantly improved and conformed to the image’s compositional characteristics, and the inpainting time efficiency improved, establishing a good foundation for restoring ancient murals.