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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. LefebvreShadow 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 Leaf Cluster Impostors for Tree Rendering with Parallax(The Eurographics Association, 2005) Garcia, Ismael; Sbert, Mateu; Szirmay-Kalos, László; John Dingliana and Fabio GanovelliThis 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 Hatching for Motion Picture Production(The Eurographics Association and Blackwell Publishing Ltd., 2011) Umenhoffer, Tamás; Szécsi, László; Szirmay-Kalos, László; M. Chen and O. DeussenThis paper presents a hatching algorithm which - while also allows for an implementation in real-time - is integrated into the production pipeline of computer generated motion picture. Motion picture production pipelines impose special functional and quality requirements. From the functional point of view, the stages of modeling, 3D rendering, and compositing form a pipeline without feed-back, and frames are rendered independently, possibly on different computers. Thus, no temporal data can be shared between them while flicker free animation needs to be generated. Quality requirements can be grasped as that of dual consistency: the generated hatching must consistently follow object movement and deformation, and, at the same time, it should have a consistent pattern and density in image-space to provide the hand-crafted look. In order to meet both requirements, we apply a particle based method and develop an image-space density control mechanism using rejection sampling and low- discrepancy sequences. We also discuss the decomposition of rendering tasks according to the main stages of the production pipeline and demonstrate how the artist can define the illustration style in a convenient way.Item Crystal Scattering Simulation for PET on the GPU(The Eurographics Association, 2011) Magdics, Milán; Szirmay-Kalos, László; N. Avis and S. LefebvreThis paper presents a fast algorithm to simulate inter-crystal scattering to increase the accuracy of Positron Emission Tomography (PET). Theoretically, inter-crystal scattering computation would require the solution of a particle transport problem, which is quite time consuming. However, most of this calculation can be ported to a pre-processing phase, taking advantage of the fact that the structure of the detector is fixed. Pre-computing the scattering probabilities inside the crystals, the final system response is the convolution of the geometric response obtained with the assumption that crystals are ideal absorbers and the crystal transport probability matrix. This convolution is four-dimensional which poses complexity problems as the complexity of the naive convolution evaluation grows exponentially with the dimension of the domain. We use Monte Carlo method to attack the curse of dimension. We demonstrate that these techniques have just negligible overhead.Item Efficient Voxel Marking for Hierarchical Volumetric Fusion(The Eurographics Association, 2016) Szirmay-Kalos, László; Tóth, Balázs; Umenhoffer, Tamás; Luis Gonzaga Magalhaes and Rafal MantiukWhen fusing depth images into a 3D volumetric model, a crucial task is to mark macro-cells as empty or as intersected by the noisy surface represented by the depth image. This paper proposes a simple marking algorithm for the GPU implementation of hierarchical volumetric fusion. The method is based on multi-level DDA ray-casting. The GPU implementation is of scattering type, but we also show a solution to avoid atomic writes, which improves performance.Item Real-Time Rendering of Cloudy Natural Phenomena with Hierarchical Depth Impostors(The Eurographics Association, 2005) Ummenhoffer, Tamás; Szirmay-Kalos, László; John Dingliana and Fabio GanovelliThis paper presents a real-time method to realistically render dynamic participating media under changing lighting conditions. In order to cope with performance requirements, the volume is built of instances of particle blocks. The simulation and rendering happen on two levels, on the block level and on the volume level. On the volume level blocks are replaced by depth impostors, which allows for very fast recalculation of the cloud illumination. Including depth information into block impostors our technique also eliminates billboard clipping artifacts when the participating medium contains objects. The proposed method can render swirling clouds and smoke on high frame rates, and can be used in real-time applications.Item Fast Approximation of Multiple Scattering in Inhomogeneous Participating Media(The Eurographics Association, 2009) Szirmay-Kalos, László; Liktor, Gábor; Umenhoffer, Tamás; Tóth, Balázs; P. Alliez and M. MagnorThis paper presents a fast approximation for the solution of the radiative transfer equation in inhomogeneous participating media. This scheme traces rays from the point light creating spherical wavefronts. While we march on a particular ray, we assume that other rays find similar material properties, which allows the solution of the diffusion equation for this ray. The proposed approximation of the scattered component can be computed in parallel with obtaining the direct term at practically no additional cost. The approximation may be used for direct visualization, an initial guess for an iterative solution, or for the main part of a Monte Carlo solution.Item Real-time Control and Stopping of Fluids(The Eurographics Association, 2013) Zsolnai, Károly; Szirmay-Kalos, László; Miguel Chover and A. Augusto de SousaIn this paper we address the fluid control problem, where an arbitrary density distribution (a shape of any kind) is given, and forces are exerted to get the fluid to flow into this shape and stop when the target distribution is reached. We present a real-time solution.Item Photon Map Gathering on the GPU(The Eurographics Association, 2005) Czuczor, Szabolcs; Szirmay-Kalos, László; Szécsi, László; Neumann, László; John Dingliana and Fabio GanovelliPhoton mapping methods obtain the indirect illumination of a point by finding those photon hits that arrived at the neighborhood of the point on the object surface. This paper proposes a method that stores the photon hits in a texture of the graphics hardware and replaces the traditional kd-tree based neighborhood searches by the filtering of this texture. This step finds the irradiance of all points (i.e. all texels) simultaneously in a single step, thus the average irradiance of a point can be obtained by a single texture lookup. Using this approach we can port the final gathering step of photon mapping to the graphics hardware (GPU). The CPU is only responsible for generating new light paths and updating the unfiltered photon map. Thanks to the optimal subdivision of the computation work between the the CPU and the GPU, the proposed algorithm can render globally illuminated scenes interactively.Item Automatic Parameter Control for Metropolis Light Transport(The Eurographics Association, 2013) Zsolnai, Károly; Szirmay-Kalos, László; M.- A. Otaduy and O. SorkineSophisticated global illumination algorithms usually have several control parameters that need to be set appropriately in order to obtain high performance and accuracy. Unfortunately, the optimal values of these parameters are scene dependent, thus their setting is a cumbersome process that requires significant care and is usually based on trial and error. To address this problem, this paper presents a method to automatically control the large step probability parameter of Primary Sample Space Metropolis Light Transport (PSSMLT). The method does not require extra computation time or pre-processing, and runs in parallel with the initial phase of the rendering method. During this phase, it gathers statistics from the process and computes the parameters for the remaining part of the sample generation. We show that the theoretically proposed values are close to the manually found optimum for several complex scenes.