Tweakable light and shade for cartoon animation.

ABSTRACTLight and shade in the context of non-photorealistic imaging, such as digital cel animation, are semantic notations, rather than physical phenomena. Therefore stylized light and shade should be intentionally animated instead of simulated. This paper proposes an intuitive, direct manipulation method for animating stylized light and shade in real-time. Our method provides intuitive click-and-drag operations for translating and deforming the shaded areas, including rotation, directional scaling, splitting, and squaring of high-lights, all without tedious parameter tuning. Our prototype system demonstrates the algorithms in our method, which are implemented along with a real-time cartoon shader on commodity graphics hard-ware. This system allows the interactive creation of stylized shading keyframes for animations, illustrating the effectiveness of the proposed techniques.