Stylized Highlights for Cartoon Rendering and Animation

ows are symbolic in that they imply an artistic interpretation of the characters and scene. For example, lighting plays an important role in suggesting a scene’s mood, while a character’s shadow shows where the character is standing. Highlighting also describes various aspects of the characters and objects in the scene. The highlight examples shown in Figure 1 were made with traditional cel animation techniques. In Figure 1a, we see a highlight on the swords, portraying that the swords are flat and shiny like plane glasses, and that they are so sharp that the heroine might be wounded in the next frame. The highlight on the monster’s claws in Figure 1b suggests that the claws are very hard, and that they can hurt someone easily. In Figure 1c the highlight on the rear window of a car shows that the window is somewhat rounded, since the highlight area is not a simple rectangle, but a little bit deformed. This highlight could be a kind of environment reflection or refraction, rather than the brightest area on the rear window. In addition the highlight just shows the area where something is reflected; we don’t see what is actually reflected on the window. As these examples show, a highlight for cel animation must be a semantic notation rather than a part of physics. The highlight shape is relatively simple but not always rounded, suggesting stylistic, hand-drawn shape variations. Moreover, for augmenting the presence of highlighted objects in the animated scene, the highlight animation feature is indispensable. Hybrid use of 3D and hand-drawn characters and scenes has achieved great success in the cel animation industry. With hybrids, you would usually add cartoon shade to 3D objects to fit into the traditional celanimated scene. As shown in Figure 2a, with a character made of a 3D object, you could photorealistically render the highlight using a standard local shading model. Introducing a threshold of specular intensity in the standard model gives the highlight a simpler configuration, such as Figure 2b. However, neither of these highlights is suited for cel animation (Figure 2a is too realistic, and Figure 2b is too simple). As illustrated in Figure 1, we want more cartoon-like highlights. Therefore, in making cartoon-style highlights for 3D objects, we must simultaneously meet the following practical requirements: