Efficient Hair Rendering under Dynamic, Low-Frequency Environmental Light Using Spherical Harmonics

Xiaoxiong XING  Yoshinori DOBASHI  Tsuyoshi YAMAMOTO  Yosuke KATSURA  Ken ANJYO  

IEICE TRANSACTIONS on Information and Systems   Vol.E98-D   No.2   pp.404-411
Publication Date: 2015/02/01
Online ISSN: 1745-1361
DOI: 10.1587/transinf.2014EDP7203
Type of Manuscript: PAPER
Category: Computer Graphics
hair rendering,  spherical harmonics,  environmental light,  voxelization,  

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We present an algorithm for efficient rendering of animated hair under a dynamic, low-frequency lighting environment. We use spherical harmonics (SH) to represent the environmental light. The transmittances between a point on a hair strand and the light sources are also represented by SH functions. Then, a convolution of SH functions and the scattering function of a hair strand is precomputed. This allows us to efficiently compute the intensity at a point on the hair. However, the computation of the transmittance is very time-consuming. We address this problem by using a voxel-based approach: the transmittance is computed by using a voxelized hair model. We further accelerate the computation by sampling the voxels. By using our method, we can render a hair model consisting of tens of thousands of hair strands at interactive frame rates.