Andrea Weidlich

Arbitrarily layered micro-facet surfaces

In this paper we present a method to combine several micro-facet based surface layers into a single unified, expressive BRDF model that is easy to use. The restriction to micro-facet based layers constitutes no loss of generality, since both perfectly specular and perfectly diffuse surfaces can be seen as limit cases of the micro-facet approach. Such multi-layered surfaces can be used to re-create the appearance of a wide range of different materials, and yield good results without having to perform explicit sub-surface scattering computations. This is achieved through suitable approximations and simplifications of the scattering within the simulated layered surface, while still taking absorption and total internal reflection into account. We also discuss the corresponding probability distribution function that is needed for sampling purposes, and investigate how the flexibility of this new approach is best put to use.

A reflectance model for diffuse fluorescent surfaces

Fluorescence is an interesting and visually prominent effect, which has not been fully covered by Computer Graphics research so far.While the physical phenomenon of fluorescence has been addressed in isolation, the actual reflection behaviour of real fluorescent surfaces has never been documented, and no analytical BRDF models for such surfaces have been published yet.This paper aims to illustrate the reflection properties typical for diffuse fluorescent surfaces, and provides a BRDF model based on a layered microfacet approach that mimics them.

Realistic rendering of birefringency in uniaxial crystals

In this article we derive the complete set of formulas needed to generate physically plausible images of uniaxial crystals. So far no computer graphics publication contains all the formulas one needs to compute the interaction of light with such crystals in a form that is useable by a graphics application, especially if a polarization-aware rendering system is being used. This paper contains the complete derivation of the Fresnel coefficients for birefringent transparent materials, as well as for the direction cosines of the extraordinary ray and the Mueller matrices necessary to describe polarization effects. The formulas we derive can be directly used in a ray based renderer, and we demonstrate these capabilities in test scenes.

Hero wavelength spectral sampling

We present a spectral rendering technique that offers a compelling set of advantages over existing approaches. The key idea is to propagate energy along paths for a small, constant number of changing wavelengths. The first of these, the hero wavelength, is randomly sampled for each path, and all directional sampling is solely based on it. The additional wavelengths are placed at equal distances from the hero wavelength, so that all path wavelengths together always evenly cover the visible range.

Modeling and Verifying the Polarizing Reflectance of Real-World Metallic Surfaces

Using measurements of real-world samples of metals, the proposed approach verifies predictions of bidirectional reflectance distribution function (BRDF) models. It employs ellipsometry to verify both the actual polarizing effect and the overall reflectance behavior of the metallic surfaces.

A standardised polarisation visualisation for images

We discuss issues surrounding the visualisation of the polarisation properties of light stored in the pixels of an image. In order to facilitate comparisons between the work of different researchers, and in order to aid the development and debugging of polarisation-capable rendering systems, we propose a set of four standardised, easily comprehensible visualisations. These cover all aspects of polarisation that are relevant for rendering research, but also for optical design tasks. However, the so-called luminance scaled overlay form of the proposed visualisations is conceivably also useful and instructive to a wider, non-technical audience, and can be used for educational purposes.

A physically plausible model for light emission from glowing solid objects

The emissive properties of glowing solid objects appear to be something that the graphics community has not considered in depth before. While the volumetric emission of plasma, i.e. flames, has been discussed numerous times, and while the emission characteristics of entire luminaires can be handled via IESNA profiles, the exact appearance of glowing solid objects appears to have eluded detailed scrutiny so far. In this paper, we discuss the theoretical background to thermally induced light emission of objects, describe how one can handle this behaviour with very little effort in a physically based rendering system, and provide examples for the visual importance of handling this in a plausible fashion.

Modeling aventurescent gems with procedural textures

In this paper we present the results of an investigation on how one can model aventurescence, an interesting and optically appealing property of some gemstones. Our goal was to find a method that is both efficient and reasonably realistic, and that can still be used in the context of a global illumination rendering system.

Polarised light in computer graphics

In Computer Graphics, the polarisation properties of light currently play a role in several contexts: in certain forms of highly realistic ray-based image synthesis (sometimes colloquially referred to as Polarisation Ray Tracing), in some 3D display systems, and in some material acquisition technologies. The properties of light that are behind all of these applications are basically the same, although the technologies for which this property of light is being used differ considerably. Also, the notations and mathematical formalisms used in these application areas differ to some degree as well. This course aims to provide a unified resource for those areas of computer graphics which require a working knowledge of light polarisation: rendering and material acquisition. Consequently, the course is structured into three main parts: I - Background, II - Polarisation Ray Tracing, and III - Polarised Light in Acquisition Technology. Care is taken so that the information provided in Part I is applicable to both Part II and III of the course, and is formulated in a way that emphasises the underlying similarities.

Anomalous dispersion in predictive rendering

In coloured media, the index of refraction does not decrease monotonically with increasing wavelength, but behaves in a quite non‐monotonical way. This behaviour is called anomalous dispersion and results from the fact that the absorption of a material influences its index of refraction.