Tweakable shadows for cartoon animation

The role of shadow is important in cartoon animation. Shadows in hand-drawn animation reflect the expression of the animators' style, rather than mere physical phenomena. However shadows in 3DCG cannot express such an animators' touch. In this paper we propose a novel method for editing the shadow with both advantages of hand drawn animation and 3DCG technology. In particular, we discuss two phases that enable animators to transform and deform the shadow tweakably. The first phase is that a shadow projection matrix is applied to deform the shape of the shadow. The second one is that we manipulate vectors to transform the shadow such as scaling and translation. These vectors are used in shadow volume method. The shadows are edited directably by integration of these two phases. Our approach enables animators to edit the shadow by simple mouse operations. As a result, the animators can not only produce shadows automatically but also reflect their style easily. Once the shape and location of shadow are decided by animators' style in our method, 3DCG techniques can produce consistent shadow in object motion interactively.