| With the rapid development of film and television animation industry,3D rendering techniques have been fully researched and used. People continue to pursue realistic visual effects, and global illumination (GI) technologies provide a way to render more realistic images. In the real world, objects are illuminated by direct light from the sun light and indirect light that is reflected and refracted from the ambient environments. GI is the approximation of the direct and indirect lighting effect.There are many ways to implement GI effects. Pixar, DreamWorks, and many other CG animation studios produced a lot of awesome animation works with Point Based Global Illumination (PBGI). Visual effects such as Subsurface (sss), color bleeding on diffuse surface, and Ambient Occlusion (AO) are implemented effectively with PBGI. However, the PBGI method also exists some problems. For large and complex scenes, extra storage space is required to cache the point cloud which greatly impacts on the efficiency. PBGI is a non-physics-based global illumination method. Different visual effects rely more on experiences and skills of artists. In terms of the organization and management of point cloud, as well as the processing methods of point cloud, there are many issues need to research.This paper focuses on three main aspects of PBGI research works.We presented the implementation and analysis of the coherent out-of-core point-based global illumination method. When rendering large-scale scenes, the point cloud files are much larger than which in memory. We refer to the coherent out-of-core point-based global illumination method[1] to extend its function, and then verify the correctness of rendering results. We also compare the efficiency between Bleman and the commercial renderer PRMan and analyze the results for further research and improvement of the algorithm.Double-side baking points methods are used to deal the color bleeding effects of the backward surface. When rendering scenes, backward surface is difficult to bake rightly, so it will not contribute correct color to the surfaces around it. Commercial renderers such as3Delight also have this problem when using the PBGI method. We propose a solution of double-side baking. If the backward surface is illuminated by lights, we bake the surface’s backward normal and color. If both sides are illuminates by lights, we bake the both sides. This method is integrated into the rendering engine for Maya and3DMax. With this method, we can achieve the correct GI effect. Computing the multiple bounces of diffuse reflection based on point cloud. We simulate the multiple bounces of light, iterate and update the value of the light illumination after several rebound in the point cloud. With the light bounces, the scene is brighter and shows us more details. We discuss the reasonable number of light bounces based on the law of conservation of energy.The work of this paper is a part of the National863Project Realistic Animation Rendering System Research and Application. The experimental platform is based on the Renderman Interface compatible photorealistic rendering engine which called Bleman, which is developed for the863Project. The point-based global illumination method is an important part of Bleman. With the work of this article, Bleman supports point-based global illumination rendering of complex scenes by scheduling big amount of point between memory and disks. Integrated Bleman renderer support GI feature of Maya,3Dmax and some other3D application very well. Double-side baking methods achieve a more realistic global illumination without additional points cached. We analysis the shortcomings of this paper and provide the future research work at last. |
