CrossShade: Shading Concept Sketches Using Cross-Section Curves

Cloud Shao (1) , Adrien Bousseau (2) , Alla Sheffer (3) , Karan Singh (1)

1 DGP - Dynamic Graphics Project [Toronto]
2 REVES - Rendering and virtual environments with sound
3 UBC-Computer Science - Computer Science Department

We facilitate the creation of 3D-looking shaded production drawings from concept sketches. The key to our approach is a class of commonly used construction curves known as cross-sections, that function as an aid to both sketch creation and viewer understanding of the depicted 3D shape. In particular, intersections of these curves, or cross-hairs, convey valuable 3D information, that viewers compose into a mental model of the overall sketch. We use the artist-drawn cross-sections to automatically infer the 3D normals across the sketch, enabling 3D-like rendering. The technical contribution of our work is twofold. First, we distill artistic guidelines for drawing cross-sections and insights from perception literature to introduce an explicit mathematical formulation of the relationships between cross-section curves and the ge- ometry they aim to convey. We then use these relationships to develop an algorithm for estimating a normal field from cross-section curve networks and other curves present in concept sketches. We validate our formulation and algorithm through a user study and a ground truth normal comparison. As demonstrated by the examples throughout the paper, these contributions enable us to shade a wide range of concept sketches with a variety of rendering styles.

Domaines: Synthèse d'image et réalité virtuelle [cs.GR]

Cloud Shao, Adrien Bousseau, Alla Sheffer, Karan Singh. CrossShade: Shading Concept Sketches Using Cross-Section Curves. ACM Transactions on Graphics, 2012, Proceedings of SIGGRAPH, 31 (4), ⟨10.1145/2185520.2185541⟩. ⟨hal-00703202v2⟩