2026-07-22 千葉大学
図1．粗い金属球（上段：等方的な銅、下段：異方的なアルミニウム）を同じ計算サンプル数（8 spp）で制作したCG画像の比較。
＜関連情報＞
- https://www.chiba-u.ac.jp/news/research-collab/cg.html
- https://dl.acm.org/doi/10.1145/3799902.3811194
スミスマイクロファセットBRDFにおける多重反射の高さ相互依存パス定式化のための逐次高さ事前積分 Successive Height Preintegration for a Height-Interdependent Path Formulation of Multiple Bounces in Smith Microfacet BRDFs
Siyuan Zhang, Takuya Funatomi, Yuki Fujimura, Yasuhiro Mukaigawa, Hiroyuki Kubo
SIGGRAPH Conference Papers ’26: Proceedings of the Special Interest Group on Computer Graphics and Interactive Techniques Conference Conference Papers Published: 19 July 2026
DOI:https://doi.org/10.1145/3799902.3811194
Abstract
Smith microfacet models are widely used to describe the interaction of light with surfaces. However, conventional microfacet models account for only a single bounce on microsurfaces, which leads to energy loss. To address the problem of missing energy, several unbiased methods have been proposed to compute multiple bounces on Smith microsurfaces. In addition, a position-free multiple-bounce microfacet model has been introduced by assuming that each bounce of a light path is height-independent, leading to lower variance but biased results. In this paper, we propose a novel derivation of multiple-bounce Smith microfacet bidirectional reflectance distribution functions (BRDFs) based on a partial adoption of the independent-bounce assumption. Our model treats most bounces as height-interdependent, leading to a height-interdependent path formulation. We further propose a successive height preintegration to make this formulation position-free. Although our model still exhibits an extremely small bias, it achieves lower variance than prior unbiased methods. Furthermore, we introduce a path type-aware BRDF evaluation that further reduces variance.
