[0004] The computation required to render photorealistic 3D images, such as raytracing and radiosity, is usually too high for interactive applications where view angles change constantly. Raytracing can be generally defined is a technique used in computer graphics to create realistic images by calculating the paths taken by rays of light entering the observer's eye at different angles. Raytracing mimics the way light travels to the eye. Therefore the computer has to figure out how each light interacts.
[0005] Radiosity is another technique for rendering a three dimensional ("3D") scene that provides realistic lighting. Generally, the theory behind radiosity mapping is that you should be able to approximate the radiosity of an entire object by precalculating the radiosity for a single point in space, and then applying it to every other point on the object. This is because, among other things points in space that are close together all have approximately the same lighting. Radiosity programs are usually complementary to raytracing programs, with the radiosity calculations forming a pre-rendering section.
[0006] Many optimization methods have been used in the past to try to improve the real-time photorealistic rendering performance. Most methods optimize the update of model data structure in dealing with the dynamic aspect. Ray-caching or Render-caching approaches are similar but are limited to the previously viewed angle. In addition, the approximation is not utilized to speed up the calculation. One way to optimize raytracing is by fixing the lighting and fixing the viewing angle. In doing so, when a surface changes, you can cache the previously calculated result for a point in space. However, if the viewing angle does change, even if the rest of the data does not change, raytracing forces you to traverse each triangle again.
[0007] Another optimization method would be to precompute the result for a specific material so another calculation becomes unnecessary. A main concern with raytracing is to organize the algorithm, so that not all of the triangles have to be visited during calculation, particularly those not visible to the screen.
[0008] Another approach is similar to precomputation but different in the method of precomputation and the way to store the precomputed ideas. This approach is found in "Precomputed Radiance Transfer for Real-Time Rendering in Dynamic, Low-Frequency Lighting Environments" (Sloan, Kuatz, and Snyder) Proc. of SIGGRAPH '02, pp. 527-536, 2002. This approach exploits the characteristics of the low variant order of lighting environment. It precomputes the transfer scalar function and vector matrix which can significantly accelerate the final rendering stage. However, the radiance transfer function and vector matrix was a sampled space of the actual model surface. It approximates across the sample space. However, the idea in "Precomputed Radiance Transfer for Real-Time Rendering in Dynamic, Low-Frequency Lighting Environments" is not surface point based.
