Interactive high fidelity visualization of complex materials on the GPU

Documento submetido para revisão pelos pares. A publicar em Computers & Graphics. ISSN 0097-8493. 37:7 (nov. 2013) p. 809–819High fidelity interactive rendering is of major importance for footwear designers, since it allows experimenting with virtual prototypes of new products, rather than producing expensive physical mock-ups. This requires capturing the appearance of complex materials by resorting to image based approaches, such as the Bidirectional Texture Function (BTF), to allow subsequent interactive visualization, while still maintaining the capability to edit the materials' appearance. However, interactive global illumination rendering of compressed editable BTFs with ordinary computing resources remains to be demonstrated. In this paper we demonstrate interactive global illumination by using a GPU ray tracing engine and the Sparse Parametric Mixture Model representation of BTFs, which is particularly well suited for BTF editing. We propose a rendering pipeline and data layout which allow for interactive frame rates and provide a scalability analysis with respect to the scene's complexity. We also include soft shadows from area light sources and approximate global illumination with ambient occlusion by resorting to progressive refinement, which quickly converges to an high quality image while maintaining interactive frame rates by limiting the number of rays shot per frame. Acceptable performance is also demonstrated under dynamic settings, including camera movements, changing lighting conditions and dynamic geometry.Work partially funded by QREN project nbr. 13114 TOPICShoe and by National Funds through the FCT - Fundação para a Ciência e a Tecnologia (Portuguese Foundation for Science and Technology) within projectPEst-OE/EEI/UI0752/2011

Generalized visual information analysis via tensorial algebra

High order data is modeled using matrices whose entries are numerical arrays of a fixed size. These arrays, called t-scalars, form a commutative ring under the convolution product. Matrices with elements in the ring of t-scalars are referred to as t-matrices. The t-matrices can be scaled, added and multiplied in the usual way. There are t-matrix generalizations of positive matrices, orthogonal matrices and Hermitian symmetric matrices. With the t-matrix model, it is possible to generalize many well known matrix algorithms. In particular, the t-matrices are used to generalize the SVD (Singular Value Decomposition), HOSVD (High Order SVD), PCA (Principal Component Analysis), 2DPCA (two Dimensional PCA) and GCA (Grassmannian Component Analysis). The generalized t-matrix algorithms, namely TSVD, THOSVD, TPCA, T2DPCA and TGCA, are applied to low-rank approximation, reconstruction and supervised classification of images. Experiments show that the t-matrix algorithms compare favourably with standard matrix algorithms

Flat Bidirectional Texture Functions

Highly-realistic materials in computer graphics are computationally and memory demanding. Currently, the most versatile techniques are based on Bidirectional Texture Functions (BTFs), an image-based approximation of appearance. Extremely realistic images may be quickly obtained with BTFs at the price of a huge amount of data. Even though a lot of BTF compression schemes have been introduced during the last years, the main remaining challenge arises from the fact that a BTF embeds many different optical phenomena generated by the underlying meso-geometry (parallax effects, masking, shadow casting, inter-reflections, etc.). We introduce a new representation for BTFs that isolates parallax effects. On one hand, we built a flattened BTF according to a global spatial parameterization of the underlying meso-geometry. On the other hand, we generate a set of view-dependent indirection maps on this spatial parameterization to encode all the parallax effects. We further analyze this representation on a various set of synthetic BTF data to show its benefits on view-dependent coherency, and to find the best sampling strategy. We also demonstrate that this representation is well suited for hardware acceleration on current GPUs.En Infographie, les matériaux hautement réalistes sont grand consommateurs de puissance de calculs ainsi que de mémoire. A l'heure actuelle, les techniques les plus versatiles reposent sur les fonctions de textures bidirectionnelles (BTFs) représentant une approximation à partir d'images de l'apparence des matériaux. Des images extrêmement réalistes peuvent être obtenues rapidement à l'aide de BTFs au prix d'une énorme quantité de données. Bien que de nombreux schémas de compression de BTFs aient été introduits au cours de ces dernières années, le principal challenge restant provient du fait qu'une BTF mélange différents phénomènes optiques générés par la meso-géométrie sous-jacente (effets de parallaxe ou de masquage, ombres portées, inter-réflexions, etc.), effets qui ne peuvent être que correctement gérés à l'aide d'approches appropriées. Nous introduisons une nouvelle représentation pour les BTFs qui isole les effets de parallaxes des autres effets. D'une part, nous construisons une BTF aplatie ("flattened") guidée par une paramétrisation spatiale et globale de la méso-géométrie sous-jacente. D'autre part, nous générons un ensemble de table d'indirections dans cette paramétrisation et pour chaque point de vue, afin d(encoder tous les effets de parallaxe. Nous analysons aussi cette représentation sur un ensemble de BTFs synthétiques afin de montrer l'avantage qu'elle apporte pour la cohérence dépendante du point de vue et pour trouver la meilleure stratégie d'échantillonnage. Nous montrons aussi que cette représentation est particulièrement bien adaptée pour bénéficier de l'accélération matérielle des processeurs graphiques actuels