Search Results

Now showing 1 - 10 of 39
  • Item
    Improving Shadow Map Filtering with Statistical Analysis
    (The Eurographics Association, 2011) Gumbau, Jesus; Szirmay-Kalos, László; Sbert, Mateu; Sellés, Miguel Chover; N. Avis and S. Lefebvre
    Shadow maps are widely used in real-time applications. Shadow maps cannot be filtered linearly as regular textures, thus undersampling leads to severe aliasing. This problem has been attacked by methods that transform the depth values to allow approximate linear filtering and to approaches based on statistical analysis, which suffer from light bleeding artifacts. In this paper we propose a new statistical filtering method for shadow maps, which approximates the cumulative distribution function (CDF) of depths with a power function. This approximation significantly reduces light bleeding artifacts, maintaining performance and spatial costs. Like existing techniques, the algorithm is easy to implement on the graphics hardware and is fairly scalable.
  • Item
    Informational Dialogue with Van Gogh's Paintings
    (The Eurographics Association, 2008) Rigau, Jaume; Feixas, Miquel; Sbert, Mateu; Douglas W. Cunningham and Victoria Interrante and Paul Brown and Jon McCormack
    From the pioneering work by Birkhoff, several measures have been proposed to quantify the aesthetic content of art. After Bense's application of information theory to Birkhoff's ideas, the concept of informational aesthetics appears. In this paper, we analyze a selection of van Gogh's paintings using a set of informational aesthetic measures based on the entropy of the palette, the compressibility of the image, and an information channel to capture the basic structure of the painting. The values of these measures match fairly well against the different styles in van Gogh's work and allow a quantitative description of these periods. In addition, we present two new measures which quantify the information associated with both color and canvas regions and enable us to visualize the most salient colors and elements of a painting.We believe that informational aesthetic measures can contribute to discovering relevant characteristics of a painting or of a painter's style.
  • Item
    Improving Multipath Radiosity with Bundles of Parallel Lines
    (The Eurographics Association and Blackwell Publishing Ltd, 2008) Martinez, Roel; Sbert, Mateu; Szirmay-Kalos, Laszlo
    Monte Carlo approaches use random lines to distribute the light power in the scene but the cost of creating a set of random single lines is very costly. In this paper, we present several software and hardware techniques in order to reduce the computational cost of the generation of random single lines by using bundles of parallel lines. The bundle of parallel lines is simulated with a general purpose polygon filling algorithm, like the painter s algorithm. We also present two graphics hardware implementations. The first approach uses two depth buffers in order to represent stochastically a bundle of parallel global lines. The second one uses multiple depth buffers and the aim is to exploit coherence between projection planes for each iteration. All algorithms were implemented with the multipath method.
  • Item
    Accelerating Path Tracing by Re-Using Paths
    (The Eurographics Association, 2002) Bekaert, Philippe; Sbert, Mateu; Halton, John; P. Debevec and S. Gibson
    This paper describes a new acceleration technique for rendering algorithms like path tracing, that use so called gathering random walks. Usually in path tracing, each traced path is used in order to compute a contribution to only a single point on the virtual screen. We propose to combine paths traced through nearby screen points in such a way that each path contributes to multiple screen points in a provably good way. Our approach is unbiased and is not restricted to diffuse light scattering. It complements previous image noise reduction techniques for Monte Carlo ray tracing. We observe speed-ups in the computation of indirect illumination of one order of magnitude.
  • Item
    An Information-Theoretic Ambient Occlusion
    (The Eurographics Association, 2007) González, Francisco; Sbert, Mateu; Feixas, Miquel; Douglas W. Cunningham and Gary Meyer and Laszlo Neumann
    Ambient occlusion is a powerful technique that mimics indirect global illumination at a fraction of the cost. In this paper, we introduce a new ambient occlusion technique based on information-theoretic concepts. A viewpoint quality measure is first defined using the concept of mutual information of the channel formed between a set of viewpoints and the polygons of an object. By reversing this channel we can speak of the mutual information of a polygon with respect to all viewpoints. From this polygonal information we represent a kind of ambient occlusion, which is dependent on the importance assigned to each viewpoint and helps to enhance features such as salient parts. Further, the assignation of color to each viewpoint combined with the polygonal information produces a nice visualization of the object. Examples are given with coloroid palettes and non-photorealistic rendering.
  • Item
    Visibility Complexity of a Region in Flatland
    (Eurographics Association, 2000) Rigau, Jaume; Feixas, Miquel; Sbert, Mateu
    The aim of this paper is to study the visibility complexity of different regions in a 2D scene. Based on mutual information, which we used in our previous work to define scene complexity, we propose two measures that quantify the complexity of a region from two different points of view. The knowledge of the complexity of a region can be useful to determine how difficult it is to recompute the visibility links for an animation depending on the regions visited or to obtain the complexity of the movement of a robot. We also envisage its applicability to obtain an optimal load balancing in a parallel computation by dividing the geometry in equal complexity regions.
  • Item
    View-based Shape Similarity using Mutual Information Spheres
    (The Eurographics Association, 2007) García, Francisco González; Feixas, Miquel; Sbert, Mateu; Paolo Cignoni and Jiri Sochor
    We present a new method for computing the shape similarity between 3D polygonal models using an informationtheoretic viewpoint selection framework. Given a 3D model, a sphere of viewpoints surrounding this model is used to obtain its shape signature from the mutual information of each viewpoint. This signature represents the essence of the shape from a view-based approach. Then, in order to quantify the dissimilarity between two models, their mutual information spheres are registered by minimizing the L2 distance between them. Several experiments show the discrimination capabilities of our approach and its potential suitability for object recognition.
  • Item
    Real-Time Multiple Scattering in Participating Media with Illumination Networks
    (The Eurographics Association, 2005) Szirmay-Kalos, László; Sbert, Mateu; Ummenhoffer, Tamás; Kavita Bala and Philip Dutre
    This paper proposes a real-time method to compute multiple scattering in non-homogeneous participating media having general phase functions. The volume represented by a particle system is supposed to be static, but the lights and the camera may move. Lights can be arbitrarily close to the volume and can even be inside. Real-time performance is achieved by reusing light scattering paths that are generated with global line bundles traced in sample directions in a preprocessing phase. For each particle we obtain those other particles which can be seen in one of the sample directions, and their radiances toward the given particle. This information is stored in an illumination network that allows the fast iteration of the volumetric rendering equation. The illumination network can be stored in two-dimensional arrays indexed by the particles and the directions, respectively. Interpreting these two-dimensional arrays as texture maps, the iteration of the scattering steps can be efficiently executed by the graphics hardware, and the illumination can spread over the media in real-time.
  • Item
    Leaf Cluster Impostors for Tree Rendering with Parallax
    (The Eurographics Association, 2005) Garcia, Ismael; Sbert, Mateu; Szirmay-Kalos, László; John Dingliana and Fabio Ganovelli
    This paper presents a simple method to render complex trees on high frame rates while maintaining parallax effects. Based on the recognition that a planar impostor is accurate if the represented polygon is in its plane, we find an impostor for each of those groups of tree leaves that lie approximately in the same plane. The groups are built automatically by a clustering algorithm. Unlike billboards, these impostors are not rotated when the camera moves, thus the expected parallax effects are provided. On the other hand, clustering allows the replacement of a large number of leaves by a single semi-transparent quadrilateral, which improves rendering time considerably. Our impostors well represent the tree from any direction and provide accurate depth values, thus the method is also good for shadow computation.
  • Item
    Real-time Light Animation
    (The Eurographics Association and Blackwell Publishing, Inc, 2004) Sbert, Mateu; Szecsi, Laszlo; Szirmay-Kalos, Laszlo
    Light source animation is a particularly hard field of real-time global illumination algorithms since moving light sources result in drastic illumination changes and make coherence techniques less effective. However, the animation of small (point-like) light sources represents a special but practically very important case, for which the reuse of the results of other frames is possible. This paper presents a fast light source animation algorithm based on the virtual light sources illumination method. The speed up is close to the length of the animation, and is due to reusing paths in all frames and not only in the frame where they were obtained. The possible applications of this algorithm are the lighting design and systems to convey shape and features with relighting.