Rendering Method Of Realistic Materials By Measured BRDF

Reflectance distribution function has been the focus of research topics in computer graphics, bidirectional reflectance distribution function describes the process of transmission of light at the surface, a general bidirectional reflectance distribution function describes reflected light as a four-dimensional function of incident direction and the outgoing direction. In general, we are using the bidirectional reflectance distribution function which is provided by analytical reflection model in the computer, these models are only an approximate simulation of real reflection. With the development of computer graphics, these models become more and more complex, they are using more and more underlying physics principles. It is worth mentioning that many physics-based models are based on theoretically able to measure, but in practice they are actually difficult to acquire.In recent years, the rendering demand for animation film industry is higher and higher, traditional analytical reflection model increasingly difficult to meet the requirements of the animation film industry, researching and using of the measure-based material is more and more widely.One popular measuring and using method is measure the BRDF of different incident angles and outgoing angles directly, and then use a variety of optimization techniques to fit the data to a selected analytical reflection model. This approach has some drawbacks. First, the representation of BRDF using analytical function is only an approximation of the true reflections, it’s different from real BRDF. Second, this optimization process is not guaranteed to produce a model well.Another method is acquire dense reflection measurements, and then use these tabulated measurements directly as a BRDF. This method requires to store the measurement data of all the objects in the scene, when property of some materials have changed, we have to find a material which is related to it and re-measure its reflectance.In order to meet these problems, this paper uses the BRDF measurement database provided by MIT as raw data. We use the linear analysis methods analysis of the raw data, and find the principal component of these BRDFs. On the basis of dimensional reduction, this paper reconstruct the BRDF using the low-dimensional vector and discovery the case of smallest error in the reconstruction and the minimum dimensions of the principal components, it laid a good foundation for the later BRDF deriving. In the processing of BRDF deriving, this paper use some meaningful parameters, according to this method, the users can specify main traits, and then we can calculate the direction of main traits by using support vector machine. Combined with the reconstructed method, we can derive some new and physical plausible BRDFs. In this paper, we applied both original BRDF and derived BRDF to our rendering system which is named of RenderWing, by using it, we can render realistic images and it has laid a solid foundation for a wide range of applications based on measured realistic material.