Tuesday, December 4, 2007

 

Photo-realistic Rendering of Metallic Car Paint from Image-Based Measurements




Martin Rump, Gero Müller, Ralf Sarlette, Dirk Koch, Reinhard Klein
EG 2008


Abstract
State-of-the-art car paint shows not only interesting and subtle angular dependency but also significant spatial variation. Especially in sunlight these variations remain visible even for distances up to a few meters and give the coating a strong impression of depth which cannot be reproduced by a single BRDF model and the kind of procedural noise textures typically used. Instead of explicitly modeling the responsible effect particles we propose to use image-based reflectance measurements of real paint samples and represent their spatial varying part by Bidirectional Texture Functions (BTF). We use classical BRDF models like Torrance-Sparrow to represent the reflection behavior of the base paint and the highly specular finish and demonstrate how the parameters of these models can be derived from the BTF measurements. For rendering the image-based spatially varying part is compressed and efficiently synthesized. This paper introduces the first hybrid analytical and image-based representation for car paint and enables the photo-realistic rendering of all significant effects of highly complex coatings.

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Thursday, November 22, 2007

 

Car-Paint rendering paper accepted at Eurographics 2008


Our paper "Photo-realistic Rendering of Metallic Car Paint from Image-Based Measurements" has been accepted as full paper at Eurographics 2008. Additional information will follow soon.

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Monday, September 10, 2007

 

Eurographics 2007 Tutorial



Together with Hendrik Lensch and Michael Goesele I co-presented the tutorial "Capturing Reflectance - From Theory to Practice" at Eurographics 2007 in Prague. The tutorial's website can be found here.

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Monday, May 21, 2007

 

Procedural Editing of Bidirectional Texture Functions

Gero Müller, Ralf Sarlette, Reinhard Klein
EGSR 2007



Abstract
Measured material representations like Bidirectional Texture Functions or Reflectance Fields offer very realistic appearance but the user is currently not capable of changing this appearance in an effective and intuitive way. Such editing operations would require a low-dimensional but expressive model for appearance that exposes only a small set of intuitively editable parameters (1D-sliders, 2D-maps) to the user but preserves all visually relevant details.
In this paper we present a novel editing technique for complex spatially varying materials. It is based on the observation that we are already good in modeling the basic geometric structure of many natural and man-made materials but still have not found effective models for the detailed small-scale geometry and the interaction of light with these materials. Our main idea is to use procedural geometry to define the basic structure of a material and then to enrich this structure with the BTF information captured from real materials. By employing recent algorithms for real-time texture synthesis and BTF compression our technique allows interactive editing.

paper (pdf)

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Wednesday, May 16, 2007

 

BTF editing paper accepted at EGSR 2007

Our paper about "Procedural Editing of Bidirectional Texture Functions" has been accepted at the Eurographics Symposium on Rendering. Additional information will follow soon.

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Friday, May 11, 2007

 

BTF research links

I've just made a brief web search on BTFs and found some new and interesting links and papers.
Obviously BTFs are still a very active area of research ;-)

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Gero's graphics research blog startet

On this page you find news and abstracts of current and previous research I've done in the graphics group of Prof. Reinhard Klein. As you can see most of my research deals with Bidirectional Texture Functions (BTF) and other image-based appearance representations. Details on our measurement lab at the University of Bonn and downloadable BTF samples can be found at http://btf.cs.uni-bonn.de/.

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Data-driven Local Coordinate Systems for Image-Based Rendering

Gero Müller, Ralf Sarlette, Reinhard Klein
Eurographics 2006


Abstract

Image-based representations of an object profit from known geometry. The more accurate this geometry is known, the better corresponding pixels in the different images can be aligned, which leads to less artifacts and better compression performance. For opaque objects the per-pixel data can then be interpreted as a sampling of the BRDF at the respective surface point. In order to parameterize this sampled data a coordinate frame has to be defined. In previous work this coordinate frame was either the global frame or a local frame derived from the base geometry. Both approaches lead to misalignments between sample vectors: Features of basically very similar BRDFs will be shifted to different regions in the sample vector leading to poor compression performance. In order to improve alignment between the sampled BRDFs in image-based rendering, we propose an optimization algorithm which determines consistent coordinate frames for every sample point on the object surface. This way we efficiently align the features even of anisotropic reflection functions and reconstruct approximate local coordinate frames without performing an explicit 3D-reconstruction. The optimization is calculated efficiently by exploiting the Fourier-shift theorem for spherical harmonics. In order to deal with different materials in a scene, the technique is combined with a clustering algorithm. We demonstrate the utility of our method by applying it to BTFs and 6D surface reflectance fields.


paper (pdf)

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Verification of Rendering Quality from Measured BTFs

Jan Meseth, Gero Müller, Florian Röder, Reinhard Klein, Michael Arnold
APGV 2006

Abstract
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.

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Rapid Synchronous Acquisition of Geometry and Appearance of Cultural Heritage Artefacts

Gero Müller, Gerhard Bendels, Reinhard Klein
VAST 2005


Abstract
In order to produce visually appealing digital models of cultural heritage artefacts, a meticulous reconstruction of the 3D geometry alone is often not sufficient, as colour and reflectance information give essential clues of the object's material. Standard texturing methods are often only able to overcome this fact under strict material and lighting condition limitations. The realistic reconstruction of complex yet frequently encountered materials such as fabric, leather, wood or metal is still a challenge. In this paper, we describe a novel system to acquire the 3D-geometry of an object using its visual hull, recorded in multiple 2D images with a multi-camera array. At the same time, the material properties of the object are measured into Bidirectional Texture Functions (BTF), that faithfully capture the mesostructure of the surface and reconstruct the look-and-feel of its material. The high rendering fidelity of the acquired BTF texture data with respect to reflectance and self-shadowing also alleviates the limited precision of the visual hull approach for 3D geometry acquisition.

paper (pdf)

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Fractional Fourier Texture Masks: Guiding Near-Regular Texture Synthesis

André Nicoll, Jan Meseth, Gero Müller, Reinhard Klein
Eurographics 2005

Abstract
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 sampling-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.


paper (pdf)

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Acquisition, Synthesis and Rendering of Bidirectional Texture Functions

Gero Müller, Jan Meseth, Mirko Sattler, Ralf Sarlette, Reinhard Klein
Computer Graphics Forum, Volume 24, Number 1, 2005


Abstract
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.

(Download from publishers website)

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Classification for Fourier Volume Rendering

Zoltán Nagy, Gero Müller, Reinhard Klein
Pacific Graphics 2004



Abstract
In the last decade, Fourier Volume Rendering (FVR) has obtained considerable attention due to its O(N^2 logN) rendering complexity, where O(N^3) is the volume size. Although ordinary volume rendering has O(N^3) rendering complexity, it is still preferred over FVR for the main reason, that FVR offers bad localization of spacial structures. As a consequence, it was assumed, that it is hardly possible to apply 1D transfer functions, which arbitrarily modify voxel values not only in dependence of the position, but also the voxel value. We show that this assumption is not true for threshold operators. Based on the theory of Fourier series, we derive a FVR method, which is capable of integrating all sample points greater (or alternatively, lower) than an iso-value τ during rendering, where τ can be modified interactively during the rendering session. We compare our method with other approaches and we show examples on well-known datasets to illustrate the quality of the renderings.

paper (pdf)

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Reflectance Field based real-time, high-quality Rendering of Bidirectional Texture Functions

Jan Meseth, Gero Müller, Reinhard Klein
Computers and Graphics, Volume 28, No.1, 2004


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.


paper (pdf)

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Fast Environmental Lighting for Local-PCA Encoded BTFs

Gero Müller, Jan Meseth, Reinhard Klein
Computer Graphics Internation 2004


Abstract
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 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.

paper (pdf)

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Compression and real-time Rendering of measured BTFs using local PCA

Gero Müller, Jan Meseth, Reinhard Klein
Vision, Modeling and Visualization 2003


Abstract
The Bidirectional Texture Function (BTF) is a suitable representation for the appearance of highly detailed surface structures under varying illumination and viewing conditions. In most current approaches the BTF is aquired by a series of images of a flat probe taken under different light and camera positions. Due to its huge size, real-time rendering of objects textured with this six-dimensional data requires suitable approximations.
In this paper we present a new approach for BTF-compression and real-time rendering using much less memory than other comparable approaches whilst achieving similar quality. Our method exploits a BRDF-wise arrangement of the data and employs a flexible generalization of the well-known Principal Component Analysis (PCA) named local PCA for the data compression.


paper (pdf)

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