CrossShade: Shading Concept Sketches Using Cross-Section Curves

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.

@Article{SBSS12,
  author       = "Shao, Cloud and Bousseau, Adrien and Sheffer, Alla and Singh, Karan",
  title        = "CrossShade: Shading Concept Sketches Using Cross-Section Curves",
  journal      = "ACM Transactions on Graphics (SIGGRAPH Conference Proceedings)",
  number       = "4",
  volume       = "31",
  year         = "2012",
  url          = "http://www-sop.inria.fr/reves/Basilic/2012/SBSS12"
}