Jan Meseth

Acquisition, Synthesis, and Rendering of Bidirectional Texture Functions

One of the main challenges in computer graphics is still the realistic rendering of complex materials such as fabric or skin. The difficulty arises from the complex meso structure and reflectance behavior defining the unique look‐and‐feel of a material. A wide class of such realistic materials can be described as 2D‐texture under varying light‐ and view direction, namely, the Bidirectional Texture Function (BTF). Since an easy and general method for modeling BTFs is not available, current research concentrates on image‐based methods, which rely on measured BTFs (acquired real‐world data) in combination with appropriate synthesis methods. Recent results have shown that this approach greatly improves the visual quality of rendered surfaces and therefore the quality of applications such as virtual prototyping. This state‐of‐the‐art report (STAR) will present the techniques for the main tasks involved in producing photo‐realistic renderings using measured BTFs in details.

Reflectance field based real-time, high-quality rendering of bidirectional texture functions

Abstract The bidirectional texture function (BTF) is a suitable representation for the appearance of highly detailed surface structures under varying illumination and viewing conditions. Since real-time rendering of the full BTF data is currently not feasible, approximations of the six-dimensional BTF are used such that the amount of data is reduced and current graphics hardware can be exploited. While existing methods work well for materials with low-depth variation, realism is lost if the depth variation grows. In this article we analyze this problem and devise a new real-time rendering paradigm based on linear interpolation of reflection fields, which provides significant improvements with respect to realism for such highly structured materials without sacrificing the general applicability and speed of previous algorithms. We propose real-time rendering algorithms for this new method supporting either point light sources or image-based lighting and demonstrate the capabilities of our new approach with several examples.

Fast environmental lighting for local-PCA encoded BTFs

Rendering geometric models with complex surface materials in arbitrary lighting environments is a challenging problem. In order to relight and render geometries covered with complex, measured BTFs two problems have to be addressed: the memory problem resulting from the large size of the measured BTF data and the light integration problem resulting from summing up the contributions from all measured light-sources. In this paper we describe how highly efficient BTF compression methods like local-PCA and suitable representations of environmental light based on spherical harmonics can be combined leading to fast environmental lighting for efficiently encoded BTFs. As a side effect the method supports precomputed radiance transfer

Verification of rendering quality from measured BTFs

One of the most important, still unsolved problems in computer graphics is the generation of predictive imagery, i.e., images that represent perfect renditions of reality. Such perfect images are required in application areas like Virtual Prototyping for making reliable decisions in the costly design development of novel products like cars and airplanes. Recently, measured material properties received significant attention since they enable generation of highly accurate images that appear to be predictive at a first glance.In this work we investigate the degree of realism that can be achieved using measured bidirectional texture functions (BTFs) by comparing photographs and rendered images at two scales. To analyze the realism of rendered images at a coarse scale, we compare the light distribution resulting from standard materials to the one from measured BTFs by automatic procedures. At a fine scale, accurate reproduction of material structures is checked by a psychophysical study. Our results show that measured BTFs lead to much more accurate results than standard materials at both scales.

Fast and memory efficient view-dependent trimmed NURBS rendering

The problem of rendering large trimmed NURBS models at interactive frame rates is of great interest for industry, since nearly all their models are designed on the basis of this surface type. Most existing approaches first transform the NURBS surfaces into polygonal representation and subsequently build static levels of detail upon them, as current graphics hardware is optimized for rendering triangles. lit this work, we present a method for memory efficient, view-dependent rendering of trimmed NURBS surfaces that yields high-quality results at interactive frame rates. In contrast to existing algorithms, our approach needs not store hierarchies of triangles, since utilizing our special multiresolution seam graph data structure, we are able to generate required triangulations on the fly.

Fractional Fourier Texture Masks: Guiding Near-Regular Texture Synthesis

Recently, the special kind of near-regular texture has drawn significant attention from researchers in the field of texture synthesis. Near-regular textures contain global regular structures that pose significant problems to the popular sample-based approaches, and irregular stochastic structures that can not be reproduced by simple tiling. Existing work tries to overcome this problem by user assisted modeling of the regular structures and then relies on regular tiling. In this paper we use the concept of fractional Fourier analysis to perform a fully automatic separation of the global regular structure from the irregular structure. The actual synthesis is performed by generating a fractional Fourier texture mask from the extracted global regular structure which is used to guide the synthesis of irregular texture details. Our new method allows for automatic and efficient synthesis of a wide range of near-regular textures preserving their regular structures and faithfully reproducing their stochastic elements.

Interactive fragment tracing

One of the main challenges in real-time rendering is to enable more and more effects that were previously available in offline rendering only. An important effect among these is physically correct reflections of arbitrary objects in curved reflectors like windshields.In this paper we propose fragment tracing on the GPU as a solution to interactively realizing this effect for large scenes as employed in industrial applications. For each rasterized fragment, a ray is traced through an octree representing the original geometry and surface material. By introducing a GPU implementation of an octree traversal, for the first time hierarchical data structures can efficiently be used on the GPU. As a result, the approach allows both handling of large geometries such as those employed in virtual prototyping and accurate rendering. Several examples show the generality and achievable rendering quality of our method.

Material modelling with physical constraints

The workflows and interfaces of commercial rendering software are currently designed for believable rendering purposes. However, for predictive rendering other approaches are needed; for example, the usual approach to describe a material or a colour is to use RGB values for diffuse and specular. Since these parameters do not have a physical meaning, these approaches are clearly not suitable for physically based rendering and in particular predictive rendering where we have to deal with complex BRDFs. An investigation is missing on how existing workflows have to be changed and expanded to make them suitable for predictive rendering without losing existing workflows.