I'm very grateful to have been involved in a project with Daniel Sýkora, Ladislav Kavan, Martin Čadík, Ondřej Jamriška, Brian Whited, Maryann Simmons, and Olga Sorkine-Hornung. Our article "Ink-and-Ray: Bas-Relief Meshes for Adding Global Illumination Effects to Hand-Drawn Characters" will be appearing in ACM Transactions on Graphics. Daniel's put up a project page with a preprint.
Abstract: We present a new approach for generating global illumination renderings of hand-drawn characters using only a small set of simple annotations. Our system exploits the concept of bas-relief sculptures, making it possible to generate 3D proxies suitable for rendering without requiring side-views or extensive user input. We formulate an optimization process that automatically constructs approximate geometry sufficient to evoke the impression of a consistent 3D shape. The resulting renders provide the richer stylization capabilities of 3D global illumination while still retaining the 2D hand-drawn look-and-feel. We demonstrate our approach on a varied set of hand-drawn images and animations, showing that even in comparison to ground-truth renderings of full 3D objects, our bas-relief approximation is able to produce convincing global illumination effects, including self-shadowing, glossy reflections, and diffuse color bleeding.
And here's the accompanying video: