Transparent Visualization with Dynamic Shading for 3D Scanned Point Clouds of Cultural Heritage Objects

Three dimensional (3D) scanned point clouds offer an invaluable tool for the digital preservation of cultural heritage, capturing intricate and complex 3D structures. Transparent visualization, i.e., see-through visualization, is essential for effectively understanding these data. However, since 3D scanned point clouds do not include normal vector information, applying shading effects to reveal complex shapes is challenging. In this paper, we present a method for assigning normal vectors to 3D scanned points using a statistical approach based on principal component analysis. To resolve the ambiguity of normal vector orientations, specifically the front or back of local surfaces, we exploit the characteristics of transparent visualization. Each normal vector is oriented toward the viewpoint, enabling consistent shading across all visible points. We then apply dynamic shading by varying the light source position sequentially, which highlights different regions of the visualized object. This approach allows for a shift in focus between surface features and deeper internal structures, enhancing the understanding of the overall structure of complex 3D cultural heritage objects. We demonstrate the effectiveness of dynamic shading through its application to real 3D scanned data of cultural heritage objects with intricate internal structures.