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Now showing 1 - 5 of 5
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    Heightfield and spatially varying BRDF Reconstruction for Materials with Interreflections
    (The Eurographics Association and Blackwell Publishing Ltd, 2009) Ruiters, Roland; Klein, Reinhard
    Photo-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.
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    Completion and Reconstruction with Primitive Shapes
    (The Eurographics Association and Blackwell Publishing Ltd, 2009) Schnabel, Ruwen; Degener, Patrick; Klein, Reinhard
    We 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.
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    BTF-CIELab: A Perceptual Difference Measure for Quality Assessment and Compression of BTFs
    (The Eurographics Association and Blackwell Publishing Ltd, 2009) Guthe, Michael; Mueller, Gero; Schneider, Martin; Klein, Reinhard
    Driven by the advances in lossy compression of bidirectional texture functions (BTFs), there is a growing need for reliable methods to numerically measure the visual quality of the various compressed representations. Based on the CIE "E00 colour difference equation and concepts of its spatio-temporal extension ST-CIELab for video quality assessment, this paper presents a numerical quality measure for compressed BTF representations. By analysing the BTF in its full six-dimensional (6D) space, light and view transition effects are integrated into the measure. In addition to the compressed representation, the method only requires the source BTF images as input and thus aids the objective evaluation of different compression techniques by means of a simple numerical comparison. By separating the spatial and angular components of the difference measure and linearizing each of them, the measure can be incorporated into any linear or multi-linear compression technique. Using a per-colour-channel principal component analysis (PCA), compression rates of about 500:1 can be achieved at excellent visual quality.
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    Variational Surface Approximation and Model Selection
    (The Eurographics Association and Blackwell Publishing Ltd, 2009) Li, Bao; Schnabel, Ruwen; Jin, Shiyao; Klein, Reinhard
    We consider the problem of approximating an arbitrary generic surface with a given set of simple surface primitives. In contrast to previous approaches based on variational surface approximation, which are primarily concerned with finding an optimal partitioning of the input geometry, we propose to integrate a model selection step into the algorithm in order to also optimize the type of primitive for each proxy. Our method is a joint global optimization of both the partitioning of the input surface as well as the types and number of used shape proxies. Thus, our method performs an automatic trade-off between representation complexity and approximation error without relying on a user supplied predetermined number of shape proxies. This way concise surface representations are found that better exploit the full approximative power of the employed primitive types.
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    BTF Compression via Sparse Tensor Decomposition
    (The Eurographics Association and Blackwell Publishing Ltd, 2009) Ruiters, Roland; Klein, Reinhard
    In this paper, we present a novel compression technique for Bidirectional Texture Functions based on a sparse tensor decomposition. We apply the K-SVD algorithm along two different modes of a tensor to decompose it into a small dictionary and two sparse tensors. This representation is very compact, allowing for considerably better compression ratios at the same RMS error than possible with current compression techniques like PCA, N-mode SVD and Per Cluster Factorization. In contrast to other tensor decomposition based techniques, the use of a sparse representation achieves a rendering performance that is at high compression ratios similar to PCA based methods.