Relief Generation Using Thangka Line Drawings

Thangka is a kind of painting artwork on cotton or silk applique, depicting a Buddhist deity, scene, or mandala of some sort. It is produced by the development of Tibetan Buddhism and culture and has important significance in the development of Tibetan Buddhism and cultural exchange between Han and Tibetan. Thangka painting has rich lines and color, thus the process of drawing it is complicated and time consuming. Thangka relief is a 3D transformation of 2D Thangka painting and currently is made by carving wood manually, thus making Thangka relief based on Thangka painting is much more sophisticated and costly. Taking advantage of computer aided design, we can generate virtual relief surface in convenience.In this paper, we introduce a new practical approach for generating 3D reliefs that meet the features of Thangka relief from 2D Thangka paintings, with a small amount of interaction. In consideration of the surface complexity, we design an algorithm to generate reliefs based on Poisson equation and adjust surfaces with distance transform. With the algorithm, we can simply adjust the parameters to acquire the desired surface. The approach consists of following steps:First we get single pixel lines in the image with the improved fast parallel thinning algorithm. Then we interact with Flood Fill and Bezier curves to acquire separated regions of reliefs. For each region, we generate a height map by solving Poisson equation with Jacobi iteration, which is accelerated by GPU shader. We can adjust parameters of Poisson equation with automatic distance transform and interaction. The parameters here include the boundary constraints and surface details. With the triangulation of the height map, we have the 3D model in the region and can observe and adjust the relief in the system. Finally, we merge all the reliefs in different regions to get the whole Thangka relief.We demonstrate our technique in examples of Thangka line paintings, showing the strength of our approach in the paper. Compared with previous algorithms, reliefs generated with our approach have rich details and good continuity at the same time, similar to real Thangka reliefs. In this paper, we apply distance transform to the parameters of Poisson equation to keep the continuity of curved surfaces for the first time. The approach contributes to the editing of surfaces that need preservation of continuity. The work of our paper can be applied to the generation of reliefs with computer aided design and non-photorealistic three-dimensional reconstruction.