BRDF Representation and Acquisition

Photorealistic rendering of real world environments is important in a range of different areas; including Visual Special effects, Interior/Exterior Modelling, Architectural Modelling, Cultural Heritage, Computer Games and Automotive Design. Currently, rendering systems are able to produce photorealistic simulations of the appearance of many real-world materials. In the real world, viewer perception of objects depends on the lighting and object/material/surface characteristics, the way a surface interacts with the light and on how the light is reflected, scattered, absorbed by the surface and the impact these characteristics have on material appearance. In order to re-produce this, it is necessary to understand how materials interact with light. Thus the representation and acquisition of material models has become such an active research area. This survey of the state-of-the-art of BRDF Representation and Acquisition presents an overview of BRDF (Bidirectional Reflectance Distribution Function) models used to represent surface/material reflection characteristics, and describes current acquisition methods for the capture and rendering of photorealistic materials

Refractive Index Dependent Bidirectional Scattering Distribution Functions

Wir untersuchen die Wirkung des Eintauchens von realen Materialien in Medien mit unterschiedlichem Brechindex. In der Theorie sollte das Reflektanz-Verhalten eines Materials, das in den umgebenden Medien mit unterschiedlichen Brechungsindizes eingetaucht wird,durch die Fresnel-Gleichungen vorhergesagt werden. Wie wir jedoch zeigen, folgt nur eine Unterklasse von Materialien diesem theoretischen Modell. In der Realität zeigen viele Materialien unerwartete Effekte wie stärker lokalisierte Highlights oder eine deutliche Zunahme von spekularer Reflexion durch Mikrogeometrie. In unseren Experimenten haben wir herausgefunden, dass diese Effekte ziemlich stark variieren, und keines der bestehenden BRDF-Modelle das realistisch wiedergeben. Wir schlagen ein neues, parametrisches Modell vor, dass den Brechungsindex berücksichtigt. Wir fitten unsere Messergebnisse an das Modell und erhalten so Parameter zur Beschreibung der Reflektanz verschiedener Medien.We investigate the effect of immersing real-world materials into media of different refractive indices. In theory, the reflective and transmissive behavior of a material that is immersed into surrounding media with different refractive indices should be predicted by the Fresnel equations. However, as we show, %\todo{Ivo}{} only a subclass of materials follows this theoretical model. In reality, many materials exhibit unexpected effects such as stronger localized highlights or a significant increase in the glossy reflection due to microgeometry. In our experiments we found that the variation of these effects can be quite strong, and none of the existing BRDF models realistically reproduce these effects seen in reality. We propose a new, parametric model that takes refractive index changes into account. We fit measurements of different materials and present results to demonstrate the importance of BRDF changes for submerged objects