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Item Improving Multipath Radiosity with Bundles of Parallel Lines(The Eurographics Association and Blackwell Publishing Ltd, 2008) Martinez, Roel; Sbert, Mateu; Szirmay-Kalos, LaszloMonte 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 Stochastic Iteration for Non-diffuse Global Illumination(Blackwell Publishers Ltd and the Eurographics Association, 1999) Szirmay-Kalos, LaszloThis paper presents a single-pass, view-dependent method to solve the rendering equation, using a stochastic iterational scheme where the transport operator is selected randomly in each iteration. The requirements of convergence are given for the general case. To demonstrate the basic idea, a very simple,continuous random transport operator is examined, which gives back the light tracing algorithm incorporating Russian roulette. Then, a new mixed continuous and finite-element based iteration method is proposed, which uses ray-bundles to transfer the radiance in a single random direction. The resulting algorithm is fast, it provides initial results in seconds and accurate solutions in minutes and does not suffer from the error accumulation problem and the high memory demand of other finite-element and hierarchical approaches.Item An Analysis of Quasi-Monte Carlo Integration Applied to the Transillumination Radiosity Method(Blackwell Publishers Ltd and the Eurographics Association, 1997) Szirmay-Kalos, Laszlo; Foris, Tibor; Neumann, Laszlo; Csebfalvi, BalazsThis paper presents an enhanced transillumination radiosity method that can provide accurate solutions at relatively low computational cost. The proposed algorithm breaks down the double integral of the gathered power to an area integral that is computed analytically and to a directional integral that is evaluated by quasi-Monte Carlo techniques. Since the analytical integration results in a continuous function of finite variation, the quasi-Monte Carlo integration that follows the analytical integration will be efficient and its error can be bounded by the Koksma-Hlawka inequality. The paper also analyses the requirements of the convergence, presents theoretical error bounds and proposes error reduction techniques. The theoretical bounds are compared with simulation results.Item A Simple and Robust Mutation Strategy for the Metropolis Light Transport Algorithm(Blackwell Publishers, Inc and the Eurographics Association, 2002) Kelemen, Csaba; Szirmay-Kalos, Laszlo; Antal, Gyorgy; Csonka, FerencThis paper presents a new mutation strategy for the Metropolis light transport algorithm, which works in the unit cube of pseudo-random numbers instead of mutating in the path space. This transformation makes the integrand have lower variation and thus increases the acceptance probability of the mutated samples. Higher acceptance ratio, in turn, reduces the correlation of the samples, which increases the speed of convergence. We use both local mutations that choose a new random sample in the neighborhood of the previous one, and global mutations that make 'large steps', and find the samples independently. Local mutations smooth out the result, while global mutations guarantee the ergodicity of the process. Due to the fact that samples are generated independently in large steps, this method can also be considered as a combination of the Metropolis algorithm with a classical random walk. If we use multiple importance sampling for this combination, the combined method will be as good at bright regions as the Metropolis algorithm and at dark regions as random walks. The resulting scheme is robust, efficient, but most importantly, is easy to implement and to combine with an arbitrary random-walk algorithm.Item Ray Coherence Between a Sphere and a Convex Polyhedron(Blackwell Science Ltd and the Eurographics Association, 1992) Horvath, Tamas; Marton, Gabor; Risztics, Peter; Szirmay-Kalos, LaszloUsing the two ray coherence theorems of Ohta and Maekawa the computation time of ray tracing algorithms for scenes of spheres and convex polyhedra can be reduced considerably. This paper presents further theorems which, together with the first two, may enable further reduction in computation time.Item Real-time Light Animation(The Eurographics Association and Blackwell Publishing, Inc, 2004) Sbert, Mateu; Szecsi, Laszlo; Szirmay-Kalos, LaszloLight 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.Item Reflectance Models with Fast Importance Sampling(Blackwell Publishers Ltd and the Eurographics Association, 1999) Neumann, Laszlo; Neumann, Attila; Szirmay-Kalos, LaszloWe introduce a physically plausible mathematical model for a large class of BRDFs. The new model is as simple as the well-known Phong model, but eliminates its disadvantages. It gives a good visual approximation for many practical materials: coated metals, plastics, ceramics, retro-reflective paints, anisotropic and retro-reflective materials, etc. Because of its illustrative properties it can be used easily in most commercial software and because of its low computational cost it is practical for virtual reality. The model is based on a special basic BRDF definition, which meets the requirements of reciprocity and of energy conservation. Then a class of BRDFs is constructed from this basic BRDF with different weight functions. The definition of such weight functions requires the user to specify the profile of the highlights, from which the weight function is obtained by derivation. It is also demonstrated how importance sampling can be used with the new BRDFs.Item Compact Metallic Reflectance Models(Blackwell Publishers Ltd and the Eurographics Association, 1999) Neumann, Laszlo; Neumannn, Attila; Szirmay-Kalos, LaszloThe paper presents simple, physically plausible, but not physically based reflectance models for metals and other specular materials. So far there has been no metallic BRDF model that is easy to compute, suitable for fast importance sampling and is physically plausible. This gap is filled by appropriate modifications of the Phong, Blinn and the Ward models. The Phong and the Blinn models are known not to have metallic characteristics. On the other hand, this paper also shows that the Cook-Torrance and the Ward models are not physically plausible, because of their behavior at grazing angles. We also compare the previous and the newly proposed models. Finally, the generated images demonstrate how the metallic impression can be provided by the new models.Item Displacement Mapping on the GPU - State of the Art(The Eurographics Association and Blackwell Publishing Ltd, 2008) Szirmay-Kalos, Laszlo; Umenhoffer, TamasThis paper reviews the latest developments of displacement mapping algorithms implemented on the vertex, geometry, and fragment shaders of graphics cards. Displacement mapping algorithms are classified as per-vertex and per-pixel methods. Per-pixel approaches are further categorized as safe algorithms that aim at correct solutions in all cases, to unsafe techniques that may fail in extreme cases but are usually much faster than safe algorithms, and to combined methods that exploit the robustness of safe and the speed of unsafe techniques. We discuss the possible roles of vertex, geometry and fragment shaders to implement these algorithms. Then the particular GPU-based bump, parallax, relief, sphere, horizon mapping, cone stepping, local ray tracing, pyramidal and view-dependent displacement mapping methods, as well as their numerous variations are reviewed providing also implementation details of the shader programs. We present these methods using uniform notations and also point out when different authors called similar concepts differently. In addition to basic displacement mapping, self-shadowing and silhouette processing are also reviewed. Based on our experiences gained having reimplemented these methods, their performance and quality are compared, and the advantages and disadvantages are fairly presented.Item Deterministic Importance Sampling with Error Diffusion(The Eurographics Association and Blackwell Publishing Ltd, 2009) Szirmay-Kalos, Laszlo; Szecsi, LaszloThis paper proposes a deterministic importance sampling algorithm that is based on the recognition that delta-sigma modulation is equivalent to importance sampling. We propose a generalization for delta-sigma modulation in arbitrary dimensions, taking care of the curse of dimensionality as well. Unlike previous sampling techniques that transform low-discrepancy and highly stratified samples in the unit cube to the integration domain, our error diffusion sampler ensures the proper distribution and stratification directly in the integration domain. We also present applications, including environment mapping and global illumination rendering with virtual point sources.