Generation of Thangka relief from line drawings

Abstract

Line drawings lack the three-dimensional (3D) information of the depicted objects, which is present in 3D models and photographs based on relief-generation techniques. Therefore, creating relief surfaces from line drawings presents special research challenges. This paper creates a 3D relief model of Thangka, the Intangible Cultural Heritage of China and UNESCO, from line drawings. To obtain the relief surfaces, our approach solves Poisson equations under the constraints of gray-scale control pictures and boundary seeds of the object regions. The Thangka relief is divided into low-frequency, mid-frequency and high-frequency components. The low- and mid-frequency components respectively correspond to the height of the human body and the limbs in the relief model, and are obtained by solving the Poisson equations constrained by distance transformations. The high-frequency components correspond to the heights of local details such as eyebrows, flowers, clouds, and mountains in the relief model, and are obtained by solving the Poisson equations with boundary constraints. Finally we add the height maps of the three components and transform the resultant height map into a mesh model of the relief. The effectiveness of our approach is demonstrated in several examples.