Lit-Sphere extension for artistic rendering
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O R I G I N A L A RT I C L E
Lit-Sphere extension for artistic rendering Hideki Todo · Ken Anjyo · Shun’ichi Yokoyama
Published online: 20 April 2013 © Springer-Verlag Berlin Heidelberg 2013
Abstract The Lit-Sphere model proposed by Sloan et al. (Proceedings of Graphics Interface 2001, pp. 143–150, 2001) is a method for emulating expressive artistic shading styles for 3D scenes. Assuming that artistic shading styles are described by view space normals, this model produces a variety of stylized shading scenes beyond traditional 3D lighting control. However, it is limited to the static lighting case: the shading effect is only dependent on the camera view. In addition, it cannot support small-scale brush stroke styles. In this paper, we propose a scheme to extend the Lit-Sphere model based on light space normals rather than view space normals. Owing to the light space representation, our shading model addresses the issues of the original Lit-Sphere approach, and allows artists to use a light source to obtain dynamic diffuse and specular shading. Then the shading appearance can be refined using stylization effects including highlight shape control, sub-lighting effects, and
Electronic supplementary material The online version of this article (doi:10.1007/s00371-013-0811-7) contains supplementary material, which is available to authorized users.
brush stroke styles. Our algorithms are easy to implement on GPU, so that our system allows interactive shading design. Keywords Non-photorealistic rendering · Stylized rendering · Lit-Sphere
1 Introduction Stylized rendering techniques in computer graphics have been widely used to emulate artistic shading styles. Among them, cartoon shading is popular in a variety of production software, including Autodesk® Maya® and 3ds Max®. This approach is based on computed illumination, and effectively reproduces the abstracted shading styles of comics or cartoons. However, the shading appearance is limited to simple shading tones, whereas hand-drawn shading styles may have rich variations as follows. Figure 1 shows a typical artistic shading style. In this scheme, the artist designs complicated shading tones in the pictorial space, which cannot be simply described by the
H. Todo () · K. Anjyo OLM Digital, Inc./JST CREST, 1-8-8 Wakabayashi, Setagaya-Ku, Tokyo 154-0023, Japan e-mail: [email protected] K. Anjyo e-mail: [email protected] Present address: H. Todo University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan S. Yokoyama IMI, Kyushu University/JST CREST, Fukuoka, Japan e-mail: [email protected]
Fig. 1 Typical shading styles in an artwork (©Marvel Comics). Pictorial shading tones are enhanced with rim lighting effects and shading strokes
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Fig. 2 Lit-Sphere shading. (left) The pictorial shading tones are captured using the Lit-Sphere shading model. (center) The Lit-Sphere fails to capture the shading strokes. (right) Our approach allows the inclusion of the shading strokes
typical diffuse and specular terms. We term such shading tones
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