变化光照目标图像合成的球调和方法

Spherical Harmonics Method for Object Image Synthesis under Changing of Illumination

光照是真实感绘制技术中的一个关键因素。研究了朗伯反射的球调和表示,提出了一种基于球调和函数的任意光照目标图像生成方法。该方法在给定目标基图像及其对应光照属性的基础上,通过基图像数据矩阵的奇异值分解(SVD)分离场景环境光分量、反演计算场景反射率和表面法向量等。新光照条件下绘制图像时,采用四阶球调和函数拟合入射光和朗伯反射核计算直接光照；间接光照采用分离出的基图像环境光分量拟合。实验表明：该方法能够保证绘制精确度,适合复杂光照条件下的目标图像生成。

Illumination is a key factor in Reality rendering. We research the spherical harmonics express of Lambert reflection and propose a pure image based rendering method to synthesis image under arbitrary illumination condition based on spherical harmonics. In the method, Singular Value Decomposition （SVD） is used analytically to derive environment light part and properties of scenes from sample images, which are taken from the same view point under different point illumination condition. For Images rendering under novel lighting conditions, fourth order spherical harmonics is used to represent the illumination condition and reflectance kernel for direct illumination effect calculation; while indirect illumination one is added by environment light part derived before. Thus the method cuts the time complexity down fiercely while holding on a high accuracy simultaneously. So feature of this method is that it supplies a good algorithm to synthesis image in complex illumination environment.