Digital Conservation of Ancient Woodblock Combining Hyperspectral Imaging and Close-range Photogrammetry Technology

Abstract. The ancient woodblocks were typically used as engraving plates for printing books and served as important tools for the dissemination of culture, scholarship, and religion. However, due to the long survival time and the influence of the natural environment, the woodblocks have suffered different degrees of damage, with blurred inscriptions or lost information. Therefore, we propose a digital protection method based on hyperspectral image and close-range photogrammetry technology. Firstly, by virtue of the high spectral resolution and penetrability of hyperspectral imaging, we synthesized the image of the woodblocks with different bands selected from the hyperspectral image, which was enhanced by combining the low-light illumination map estimation (LIME) and the dark-channel algorithms. It can improve the detailed information in the woodblocks. Secondly, due to the existence of multiple damage in the woodblocks, we proposed a digital restoration method that enhance the structural information to restore cracks and missing regions in the woodblocks. During the restoration process, a curvature function was introduced into the data term to address the issue of insufficient consideration of structural information in traditional patch-based algorithms. A boundary function is incorporated to prioritize the restoration of regions with distinct structural features. The method was validated on the Tripitaka woodblocks produced during the Emperor Qian Long period of Qing Dynasty, China (A.D. 1736–1796). The experimental results show that the method can effectively restore the damage and reveal more detail information on the woodblocks. It can provide a feasible technical solution for the digital conservation of the ancient woodblocks.