Abstract: This paper presents a ray tracing-based method to speed up the global illumination with glossy surfaces by using hemispherical harmonics.In this method,the radiance samples have been achieved on the surface,then they are calculated and put into cache memory.Lastly other points around the sample points are interpolated.The incoming radiance at a point is represented with the hemispherical basis.BRDFs are defined on the Cartesian product of hemispheres.A handy method is used to calculate the radiance gradient at a point.It shows that our method improves the global illumination calculation speed much more.It has more application fields such as illumination project,high quality animation and virtual reality rendering.

Key words: global illumination, ray tracing, hemispherical harmonics, Bidirection Reflectance Distribution Function（BRDF）

摘要： 提出一种基于蒙特卡洛积分,利用半球谐函数对光滑平面进行的快速全局照明计算方法。该方法通过在光滑平面上的辐亮度进行取样,然后把其放进高速缓存器中,经过计算再对其它点进行插值。为了提高计算速度,物体表面的入射辐亮度被半球谐化,并且物体表面的双向反射率分布函数也被定义成两个半球面上的笛卡儿积。插值时,利用梯度方向插值,并且用了一种简便的方法来计算一个点的梯度。该方法能极大提高了全局照明的计算速度。这对于照明工程、高质量的动画制作及虚拟现实等领域都具有非常广阔的应用前景。

关键词: 全局照明, 光线跟踪, 半球谐函数, 双向反射率分布函数