Material Appearance Modeling

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DOME II: A Parallelized BTF Acquisition System
(The Eurographics Association, 2013) Schwartz, C.; Sarlette, R.; Weinmann, M.; Klein, R.; Reinhard Klein and Holly Rushmeier
Bidirectional Texture Functions (BTFs) provide a realistic depiction of the appearance of many real-world materials as they contain the spatially varying light scattering behavior of the material surface. Since editing of existing BTF data is still in its early stages, materials have to be measured from real-world samples. In contrast to the related Spatially Varying BRDFs (SVBRDFs), the reflectance information encoded in a BTF also includes nonlocal scattering effects and therefore does not obey energy conservation or reciprocity. While this higher degree of freedom also contributes to an increased realism, it inadvertently calls for an extensive measurement of reflectance samples, as many regularization approaches from BRDF measurement do not apply. In this paper, we present an automated, parallelized, robust, fast and transportable setup for the acquisition of BTFs from flat samples as well as 3D objects using camera and light arrays: the DOME II. In contrast to previous camera array approaches, the present setup, which is comprised of high-quality industry grade components, overcomes several issues regarding stability, reliability and precision. It achieves a well balanced state-of-the-art acquisition performance in terms of speed and quality at reasonable costs.
From Color to Appearance in the Real World
(The Eurographics Association, 2013) Ellens, M.; Mueller, G.; Lamy, F.; Reinhard Klein and Holly Rushmeier
X-Rite's declared ambition is to create a digital ecosystem for appearance; a daunting challenge that has many dimensions and has not been accomplished so far. In this short paper we sketch a path from color to full appearance which aims at solving this challenge.
Towards a Practical Gamut of Appearance Acquisition
(The Eurographics Association, 2013) Fuchs, M.; Koch, S.; Gieseke, L.; Mozer, F.; Eberhardt, B.; Reinhard Klein and Holly Rushmeier
We propose discussing the performance of appearance modeling in terms of supported material and illumination gamut. While we have a precise understanding of the cost of any given appearance modeling method, performance is intrinsically hard to express without standardized material and illumination test scenarios. This lack of vocabulary hampers comparability between alternative approaches as well as the communication with community outsiders.
Grand Challenges: Material Models in the Automotive Industry
(The Eurographics Association, 2013) Schregle, R.; Denk, C.; Slusallek, P.; Glencross, M.; Reinhard Klein and Holly Rushmeier
Material reflectance definitions are core to high fidelity visual simulation of objects within a compelling 3D scene. In the automotive industry these are used across the entire business process: from conceptualisation of a new product range, through to the final sale. However, current state-of-the-art of material representations leave much to be desired for fast and practical deployment in the industry. Even after decades of research and development, there are no interoperable standards for material models to facilitate exchange between applications. A large discrepancy also exists between the quality of material models used (and indeed the quality at which they can be displayed) across the spectrum of use-cases within the industry. Focussing on the needs of the Automotive Industry, in this position paper, we summarise the main issues that limit the effective use of material models. Furthermore, we outline specific solutions we believe could be investigated in order to address this problem. This paper is the result of a review conducted in conjunction with several key players in the automotive field.
BTF-based Material Representations: Current Challenges
(The Eurographics Association, 2013) Ruiters, R.; Klein, R.; Reinhard Klein and Holly Rushmeier
The development of Bidirectional Texture Functions (BTFs) has made it possible for a wide range of different materials to acquire their characteristic appearance from a real-world counterpart and reproduce it faithfully in a high-quality rendering, that is hard to distinguish from an actual photograph. However, they have not yet found wide-spread use in practical applications. In this paper, we discuss, from our point of view, the main reasons for this and which unanswered questions and challenges for future research in this area remain. We focus on three different aspects: How can BTFs be measured and represented more efficiently? How can they be edited intuitively? And finally, can we find a perceptual difference metric between materials?
Interactive Appearance Design in the Presence of Optically Complex
(The Eurographics Association, 2013) Schroeder, K.; Zincke, A.; Reinhard Klein and Holly Rushmeier
In this position paper, we discuss the usability of different material representations for interactive appearance design in the context of visual prototyping. We emphasize the importance of methods explicitly considering microgeometry, particularly when combined with efficient volumetric representations. Decoupling of small-scale geometric structure and optical properties allows for the most comprehensive edits while still achieving physically plausible results, even for optically complex materials such as cloth.
Material Modeling with Physical Constraints
(The Eurographics Association, 2013) Weidlich, A.; Meseth, J.; Reinhard Klein and Holly Rushmeier
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.
The MAM2014 Sample Set
(The Eurographics Association, 2014) Rushmeier, Holly; Reinhard Klein and Holly Rushmeier
Modeling the material appearance of physical materials requires access to the materials. Sets of identical physical material models were prepared for distribution at the workshop on material appearance modeling 2014 (MAM2014). The sample set is intended to facilitate the comparison of measurements and models from different laboratories and psychophysical experiments comparing simulated and physical appearance.
The Role of Visual Comparison Testing in Material Appearance Modeling
(The Eurographics Association, 2014) Meyer, Gary; Reinhard Klein and Holly Rushmeier
Material appearance modeling should involve end user testing. These tests can be visual comparison experiments where decisions made with real physical samples are compared with choices done using computer graphic simulations. This type of evaluation is necessary to determine whether simulations derived from material appearance models can be used to accomplish such tasks as the design of new products or the sale of manufactured goods. Lighting conditions, viewing circumstances, decision criteria, and user expertise can vary widely in each situation where the results of material appearance modeling are used to make a choice. An experiment is currently underway to perform such tests for automotive paint simulation.
Reducing Anisotropic BSDF Measurement to Common Practice
(The Eurographics Association, 2014) Ward, Greg; Kurt, Murat; Bonneel, Nicolas; Reinhard Klein and Holly Rushmeier
We address the problem of measuring and representing reflection and transmission for anisotropic materials without relying on mathematical models or a large sample database. By eliminating assumptions of material behavior, we arrive at a general method that works for any surface class, from metals to fabrics, fritted glazing, and prismatic films. To make data gathering practical, we introduce a robust analysis method that interpolates a sparse set of incident angle measurements to obtain a continuous function over the full 4-D domain. We then convert this interpolant to a standard representation tailored for efficient rendering and supported by a common library that facilitates data sharing. We conclude with some remaining challenges to making anisotropic BSDF measurements truly practical for rendering
Statistical Characterization of Surface Reflectance
(The Eurographics Association, 2014) Havran, Vlastimil; Sbert, Mateu; Reinhard Klein and Holly Rushmeier
The classification of surface reflectance functions as diffuse, specular, and glossy has been introduced by Heckbert more than two decades ago. Many rendering algorithms are dependent on such a classification, as different kinds of light transport will be handled by specialized methods, for example caustics require specular bounce or refraction. Due to the increasing wealth of surface reflectance models including those based on measured data, it has not been possible to keep such a characterization simple. Each surface reflectance model is mostly handled separately, or alternatively, the rendering algorithm restricts itself to the use of some subset of reflectance models. We suggest a characterization for arbitrary surface reflectance representation by standard statistical tools, namely normalized variance known as Squared-Coefficient-of-Variation (SCV).We show by videos that there is even a weak perceptual correspondence with the proposed reflectance characterization, when we use monochromatic surface reflectance and the images are normalized so they have the unit albedo.
Linear Transport Theory and Applications to Rendering
(The Eurographics Association, 2014) Jakob, Wenzel; Reinhard Klein and Holly Rushmeier
In this talk, I will give an overview of one-dimensional Linear Transport Theory, which concerns itself with the study of random scattering and absorption processes and the inference of large-scale behavior from simple local scattering models. Research over the last 75 years has led to a rich toolbox of solution techniques for these types of problems, including Monte Carlo, Diffusion Theory, H-functions, Discrete Ordinates, and the Adding-Doubling method. I will give an intuitive overview of each of these techniques and discuss advantages and disadvantages. Following this, I will discuss how this problem is relevant to rendering, where it leads to a flexible and efficient method for rendering general layered materials.
ALTA: A BRDF Analysis Library
(The Eurographics Association, 2014) Belcour, Laurent; Barla, Pascal; Pacanowski, Romain; Reinhard Klein and Holly Rushmeier
In this document, we introduce ALTA, a cross platform generic open-source library for Bidirectional Reflectance Distribution Function (BRDF) analysis. Among others, ALTA permits to estimate BRDF models parameters from measured data, to perform statistical analysis and also to export BRDF data models in a wide variety of formats.
Scanning Gonio-Photometers for Asymmetric Acquisition of Fine-structured BSDF
(The Eurographics Association, 2014) Apian-Bennewitz, Peter; Reinhard Klein and Holly Rushmeier
Results of building and running out-of-plane scanning gonio-photometers for a number of years and projects are presented. Key concepts are a fast drive system and adaptive scan pattern to sample peaks at higher angular resolution. It is suggested to scan the BSDF asymmetrically, at a finer angular resolution for the outgoing directions than the incident directions.
Quality Assurance Based on Descriptive and Parsimonious Appearance Models
(The Eurographics Association, 2015) Nielsen, J. B.; Eiriksson, E. R.; Kristensen, R. L.; Wilm, J.; Frisvad, J. R.; Conradsen, K.; Aanæs, H.; Reinhard Klein and Holly Rushmeier
In this positional paper, we discuss the potential benefits of using appearance models in additive manufacturing, metal casting, wind turbine blade production, and 3D content acquisition. Current state of the art in acquisition and rendering of appearance cannot easily be used for quality assurance in these areas. The common denominator is the need for descriptive and parsimonious appearance models. By 'parsimonious' we mean with few parameters so that a model is useful both for fast acquisition, robust fitting, and fast rendering of appearance. The word 'descriptive' refers to the fact that a model should represent the main features of the acquired appearance data. The solution we propose is to reduce the degrees of freedom by greater use of multivariate statistics.
Frontmatter: Eurographics 2015 Workshop on Material Appearance Modeling
(The Eurographics Association, 2015) Klein, Reinhard; Rushmeier, Holly; -
A Short Survey on Optical Material Recognition
(The Eurographics Association, 2015) Weinmann, M.; Klein, R.; Reinhard Klein and Holly Rushmeier
The complexity of visual material appearance as observed in the huge variation in material appearance under different viewing and illumination conditions makes material recognition a highly challenging task. In the scope of this paper, we discuss the facts that make material appearance that complex and provide a survey on technical achievements towards a reliable material recognition that have been presented in the literature so far. In addition, we discuss still open challenges that might be in the focus of future research.
Proposal for an Appearance Exchange Format
(The Eurographics Association, 2015) Mueller, Gero; Lamy, Francis; Reinhard Klein and Holly Rushmeier
In this short paper X-Rite proposes a new file format for exchanging digital material appearance. The format is a vital part of X-Rite's appearance initiative consisting of a new generation of appearance capturing devices currently under development. In order to make the usage of measured appearance as simple as possible for users, a broad support by software vendors is essential. Therefore, X-Rite aims to initiate the assembly of a consortium of hard- and software vendors, members of the scientific community and users, which would be responsible for the further development and standardization of the format.
The Material Definition Language
(The Eurographics Association, 2015) Kettner, L.; Raab, M.; Seibert, D.; Jordan, J.; Keller, A.; Reinhard Klein and Holly Rushmeier
We introduce the physically-based Material Definition Language (MDL). Based on the principle of strictly separating material definition and rendering algorithms, each MDL material is applicable across different rendering paradigms ranging from realtime over interactive solutions to advanced light transport simulation.
Linear Models for Material BTFs and Possible Applications
(The Eurographics Association, 2015) Brok, D. den; Weinmann, M.; Klein, R.; Reinhard Klein and Holly Rushmeier
Due to the richness of real-world materials, arguably one of the biggest challenges in rendering is to come up with models that describe their appearance well. The image-based bidirectional texture function (BTF) is known to be able to model many effects that are hard or impossible to reproduce with analytical reflectance models. This advantage comes at the price of demanding storage and acquisition requirements. In previous work, we have demonstrated that these requirements can be lifted to some extent by means of data-driven linear models. We give a more in-depth overview on our research on such models and summarize the applications we investigated so far, followed by an outlook on what might yet be achievable.

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