Illumination Representing And The Application In Scene Rendering Using Spherical Harmonics

As key technology of adding realism to the virtual scene, lighting is widely used in 3D games, animating Movie & TV, and 3D GIS systems. A lot of algorithms about lighting representing and scene rendering based on spherical harmonics have been presented in recent years. Unfortunately, these algorithms have many disadvantages, such as a large number of SH basis functions, disregarding shadow inter-reflected transfer and the slow velocity of ray tracing. In order to solve these problems, we did a solid and systemic research on lighting representing and scene rendering based on the latest theories and technologies in Computer Graphics and Virtual Realism. The follows are main works of this dissertation:Firstly, the spherical harmonics has been introduced to represent various illumination properties. Usually, the magnitude of the SH coefficients is very large. So it needs to compress and brings noise. To solve the problem, it provides a method to control the number of coefficients based on energy. Experiments demonstrate that the magnitude has been controlled and the result is well.Secondly, because a nine dimension linear subspace can represent a convex lambertian object under any illumination. It can get the subspaces by the spherical harmonics function. To compare with other methods, the method can deal with complicated illumination, but the shadow is not very ideal. To overtake the disadvantage, it provides a low-dimension linear subspace to get the illumination rendering through spherical harmonics. At first, it analyzes how to use spherical harmonics to approximate lambertian reflectance, then introduces how to get the reflection function by the linear subspaces, at last gives how to improve the reflection function. The research is only about convex lambertian object.Finally, the importance of precomputed radiance transfer in Real-Time scene rendering is analyzed. Comparing the existent methods , it points out the disadvantage of the algorithm using spherical harmonics is the velocity of ray tracing .To improve the algorithm, the bounding spheres has been taken and the sample directions are organized in hierarchical bins. Experiments demonstrate that the velocity has been increased at meantime time the result has not been reduced .But the research is a single object in static scene.