11 results
Search Results
Now showing 1 - 10 of 11
Item Example-based Interpolation and Synthesis of Bidirectional Texture Functions(The Eurographics Association and Blackwell Publishing Ltd., 2013) Ruiters, Roland; Schwartz, Christopher; Klein, Reinhard; I. Navazo, P. PoulinBidirectional Texture Functions (BTF) have proven to be a well-suited representation for the reproduction of measured real-world surface appearance and provide a high degree of realism. We present an approach for designing novel materials by interpolating between several measured BTFs. For this purpose, we transfer concepts from existing texture interpolation methods to the much more complex case of material interpolation. We employ a separation of the BTF into a heightmap and a parallax compensated BTF to cope with problems induced by parallax, masking and shadowing within the material. By working only on the factorized representation of the parallax compensated BTF and the heightmap, it is possible to efficiently perform the material interpolation. By this novel method to mix existing BTFs, we are able to design plausible and realistic intermediate materials for a large range of different opaque material classes. Furthermore, it allows for the synthesis of tileable and seamless BTFs and finally even the generation of gradually changing materials following user specified material distribution maps.Item Data Driven Surface Reflectance from Sparse and Irregular Samples(The Eurographics Association and John Wiley and Sons Ltd., 2012) Ruiters, Roland; Schwartz, Christopher; Klein, Reinhard; P. Cignoni and T. ErtlIn recent years, measuring surface reflectance has become an established method for high quality renderings. In this context, especially non-parametric representations got a lot of attention as they allow for a very accurate representation of complex reflectance behavior. However, the acquisition of this data is a challenging task especially if complex object geometry is involved. Capturing images of the object under varying illumination and view conditions results in irregular angular samplings of the reflectance function with a limited angular resolution. Classical data-driven techniques, like tensor factorization, are not well suited for such data sets as they require a resampling of the high dimensional measurement data to a regular grid. This grid has to be on a much higher angular resolution to avoid resampling artifacts which in turn would lead to data sets of enormous size. To overcome these problems we introduce a novel, compact data-driven representation of reflectance functions based on a sum of separable functions which are fitted directly to the irregular set of data without any further resampling. The representation allows for efficient rendering and is also well suited for GPU applications. By exploiting spatial coherence of the reflectance function over the object a very precise reconstruction even of specular materials becomes possible already with a sparse input sampling. This would be impossible using standard data interpolation techniques. Since our algorithm exclusively operates on the compressed representation, it is both efficient in terms of memory use and computational complexity, depending only sub-linearly on the size of the fully tabulated data. The quality of the reflectance function is evaluated on synthetic data sets as ground truth as well as on real world measurements.Item Heightfield and spatially varying BRDF Reconstruction for Materials with Interreflections(The Eurographics Association and Blackwell Publishing Ltd, 2009) Ruiters, Roland; Klein, ReinhardPhoto-realistic reproduction of material appearance from images has widespread use in applications ranging from movies over advertising to virtual prototyping. A common approach to this task is to reconstruct the small scale geometry of the sample and to capture the reflectance properties using spatially varying BRDFs. For this, multi-view and photometric stereo reconstruction can be used, both of which are limited regarding the amount of either view or light directions and suffer from either low- or high-frequency artifacts, respectively. In this paper, we propose a new algorithm combining both techniques to recover heightfields and spatially varying BRDFs while at the same time overcoming the above mentioned drawbacks. Our main contribution is a novel objective function which allows for the reconstruction of a heightfield and high quality SVBRDF including view dependent effects. Thereby, our method also avoids both low and high frequency artifacts. Additionally, our algorithm takes inter-reflections into account allowing for the reconstruction of undisturbed representations of the underlying material. In our experiments, including synthetic and real-world data, we show that our approach is superior to state-of-the-art methods regarding reconstruction error as well as visual impression. Both the reconstructed geometry and the recovered SVBRDF are highly accurate, resulting in a faithful reproduction of the materials characteristic appearance, which is of paramount importance in the context of material rendering.Item Fabric Appearance Benchmark(The Eurographics Association, 2020) Merzbach, Sebastian; Klein, Reinhard; Ritschel, Tobias and Eilertsen, GabrielAppearance modeling is a difficult problem that still receives considerable attention from the graphics and vision communities. Though recent years have brought a growing number of high-quality material databases that have sparked new research, there is a general lack of evaluation benchmarks for performance assessment and fair comparisons between competing works. We therefore release a new dataset and pose a public challenge that will enable standardized evaluations. For this we measured 56 fabric samples with a commercial appearance scanner. We publish the resulting calibrated HDR images, along with baseline SVBRDF fits. The challenge is to recreate, under known light and view sampling, the appearance of a subset of unseen images. User submissions will be automatically evaluated and ranked by a set of standard image metrics.Item State of the Art on 3D Reconstruction with RGB-D Cameras(The Eurographics Association and John Wiley & Sons Ltd., 2018) Zollhöfer, Michael; Stotko, Patrick; Görlitz, Andreas; Theobalt, Christian; Nießner, Matthias; Klein, Reinhard; Kolb, Andreas; Hildebrandt, Klaus and Theobalt, ChristianThe advent of affordable consumer grade RGB-D cameras has brought about a profound advancement of visual scene reconstruction methods. Both computer graphics and computer vision researchers spend significant effort to develop entirely new algorithms to capture comprehensive shape models of static and dynamic scenes with RGB-D cameras. This led to significant advances of the state of the art along several dimensions. Some methods achieve very high reconstruction detail, despite limited sensor resolution. Others even achieve real-time performance, yet possibly at lower quality. New concepts were developed to capture scenes at larger spatial and temporal extent. Other recent algorithms flank shape reconstruction with concurrent material and lighting estimation, even in general scenes and unconstrained conditions. In this state-of-the-art report, we analyze these recent developments in RGB-D scene reconstruction in detail and review essential related work. We explain, compare, and critically analyze the common underlying algorithmic concepts that enabled these recent advancements. Furthermore, we show how algorithms are designed to best exploit the benefits of RGB-D data while suppressing their often non-trivial data distortions. In addition, this report identifies and discusses important open research questions and suggests relevant directions for future work.Item Visualization Framework for the Integration and Exploration of Heterogeneous Geospatial Data(The Eurographics Association, 2009) Greß, Alexander; Klein, Reinhard; D. Ebert and J. KrügerThis paper presents an interactive visualization framework for heterogeneous geospatial data developed in context of an interdisciplinary research project that aims at the risk analysis of sea-dumped chemical weapons in the Baltic Sea. In the focus of the analysis are geophysical, hydrographical, geochemical, and biological data acquired on research cruises as well as data produced by toxic compound migration and bioaccumulation modeling. These different types of data to be visualized are represented as height fields, 2D vector maps, seismic profiles, and time-dependent scalar and vector fields. In general, these datasets are given at largely varying resolutions and geospatial extents, which makes their integration into one visualization especially challenging and requires efficient level-of-detail techniques. Furthermore, special care is taken on the appropriate integration and efficient 3D visualization of all different types of data at the same time. Several examples demonstrate the effectiveness of the resulting visualizations for collaborative analysis of the data.Item Cloth Animation and Rendering(Eurographics Association, 2002) Hauth, Michael; Etzmuss, Olaf; Eberhardt, Bernd; Klein, Reinhard; Sarlette, Ralf; Sattler, Mirko; Daubert, Katja; Kautz, JanThe area of physically-based modeling is situated in the intersection of computer science, mathematics, and physics. The animation of cloth is a particularly interesting application of physically-based modeling, because it aims at fast animation solutions for rather difficult physical problems. Moreover, it addresses one of the major difficulties in creating realistic scenes with virtual actors. The challenge of computer animation is to break down physical models for complex structures as textiles, approximate them efficiently, and run fast simulations with intelligent numerical methods. Furthermore, interactivity and collisions with other objects in the scene are challenges that have motivated much creative work over the recent years. The range of methods proposed in literature is quite large. The techniques vary from simplified methods designed for real-time applications to sophisticated methods that were designed to reproduce measured material properties. Rendering cloth is especially difficult because of its complex material properties. Software rendering can deal with these properties fairly easily, once they have been acquired, but remains too slow for interactive applications. Hardware accelerated rendering often provides a way to achieve interactive renderings, unfortunately complex materials aren’t directly supported. We will demonstrate how interactive rendering with complex materials can nonetheless be achievedItem Photo-realistic Rendering of Metallic Car Paint from Image-Based Measurements(The Eurographics Association and Blackwell Publishing Ltd, 2008) Rump, Martin; Mueller, Gero; Sarlette, Ralf; Koch, Dirk; Klein, ReinhardState-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 Cook-Torrance 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.Item Fast Distance Field Interpolation for Reconstruction of Surfaces from Contours(Eurographics Association, 1999) Klein, Reinhard; Schilling, AndreasOne simple and robust way to get a reconstruction of surfaces from a given contour stack dealing well with branching and other problems which are generally difficult to solve is based on the well known MC-algorithm. To overcome the staircase artefacts produced by the MC-algorithm Jones et. al. 3 proposed to use a distance field interpolation between the slices and to run the MC-algorithm on this distance field. The main problem of this approach is the distance field computation as it is very time consuming especially if high resolution grids (e.g. 10241024 are used. Therefore, in the original algorithm the resolution of the chosen grid is much less than the resolution of the given contour sacrificing accuracy of the resulting surface. Especially in medical applications this is not accepted by the doctors. In this paper we introduce a new method for the computation of the discrete distance field, which is a breaktrough in terms of speed and accuracy. This new method allows us to reconstruct surfaces from contour stacks with guaranteed accuracy in reasonable time. Several examples show the power of this approach.Item Completion and Reconstruction with Primitive Shapes(The Eurographics Association and Blackwell Publishing Ltd, 2009) Schnabel, Ruwen; Degener, Patrick; Klein, ReinhardWe consider the problem of reconstruction from incomplete point-clouds. To find a closed mesh the reconstruction is guided by a set of primitive shapes which has been detected on the input point-cloud (e.g. planes, cylinders etc.). With this guidance we not only continue the surrounding structure into the holes but also synthesize plausible edges and corners from the primitives intersections. To this end we give a surface energy functional that incorporates the primitive shapes in a guiding vector field. The discretized functional can be minimized with an efficient graph-cut algorithm. A novel greedy optimization strategy is proposed to minimize the functional under the constraint that surface parts corresponding to a given primitive must be connected. From the primitive shapes our method can also reconstruct an idealized model that is suitable for use in a CAD system.