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Item A Microfacet Based Coupled Specular-Matte BRDF Model with Importance Sampling(Eurographics Association, 2001) Kelemen, Csaba; Szirmay-Kalos, LaszloThis paper presents a BRDF model based on the analysis of the photon collisions with the microfacets of the surface. The new model is not only physically plausible, i.e. symmetric and energy conserving, but provides other important features of real materials, including the off-specular peak and the mirroring limit case. Using theoretical considerations the reflected light is broken down to a specular component representing single reflections and a matte component accounting for multiple reflections and re-emissions of previously absorbed photons. Unlike most of the previous models, the proportion of the matte and specular components is not constant but varies with the viewing angle. In order to keep the resulting formulae simple, several approximations are made, which are quite accurate but allow for tabulation, fast calculation and even for accurate importance sampling.Item Improved Indirect Photon Mapping withWeighted Importance Sampling(Eurographics Association, 2003) Szirmay-Kalos, Laszlo; Szecsi, LaszlThis paper offers a novel approach to the indirect photon mapping method. The placement of photons acting as virtual light sources is regarded as a cheap sampling scheme, allowing for the reuse of a complete shooting path at the cost a single shadow ray. In order to counter for its shortcomings, the variance reduction technique called weighted importance sampling is applied. This allows for the extension of the indirect photon mapping method for specular settings, because the weighting function can mimic surface BRDF characteristics disregarded by the virtual light source placement. On the other hand, weighted importance sampling also helps to eliminate the "corner spikes" caused by the fact that shooting cannot mimic the geometric factor of the connection rays. Advantages and problems are examined for several weighting schemes.Item Dependent Tests Driven Filtering in Monte-Carlo Global Illumination(Eurographics Association, 2002) Csonka, Ferenc; Szirmay-Kalos, Laszlo; Kelemen, Csaba; Antal, GyörgyThis paper presents a multi-phase algorithm to solve the global illumination problem. In the first phase dependent tests are applied, i.e. the random walks of different pixels are built from the same random numbers. The result of the first phase is used to identify homogeneous pixel groups in the image. The criterion of the formation of such groups is that averaging the color inside these groups should result in less error than handling the pixels independently. The second phase of the algorithm is a conventional random walk method that uses independent random samples in different pixels. The final result is calculated as the average of the results of the dependent tests and the lowpass filtered version of the independent tests. This low-pass filter averages the pixel values inside the homogenous groups. The algorithm takes advantage of the fact that the image can contain larger homogeneous regions that can be calculated from much less number of samples. Thus we can focus on those pixels where significant changes happen.Item Gaming in Elliptic Geometry(The Eurographics Association, 2021) Szirmay-Kalos, Laszlo; Magdics, Milán; Theisel, Holger and Wimmer, MichaelAn interesting way to explore curved spaces is to play games governed by the rules of non-Euclidean geometries. However, modeling tools and game engines are developed with Euclidean geometry in mind. This paper addresses the problem of porting a game from Euclidean to elliptic geometry. We consider primarily the geometric calculations and the transformation pipeline.Item GPUGI: Global Illumination Effects on the GPU(The Eurographics Association, 2006) Szirmay-Kalos, Laszlo; Szecsi, Laszlo; Sbert, Mateu; Nadia Magnenat-Thalmann and Katja BühlerIn this tutorial we explain how global illumination rendering methods can be implemented on Shader Model 3.0 GPUs. These algorithms do not follow the conventional local illumination model of Di- rectX/OpenGL pipelines, but require global geometric or illumination information when shading a point. In addition to the theory and state of the art of these approaches, we go into the details of a few algorithms, including mirror reflections, reflactions, caustics, diffuse/glossy indirect illumination, precomputation aided global illumination for surface and volumetric models, obscurances and tone mapping, also giving their GPU implementation in HLSL or Cg language.Item Efficient Monte Carlo and Quasi-Monte Carlo Rendering Techniques(Eurographics Association, 2003) Keller, Alexander; Kollig, Thomas; Sbert, Mateu; Szirmay-Kalos, Laszlo-Item Bregman Approach to Single Image De-Raining(The Eurographics Association, 2021) Szirmay-Kalos, Laszlo; Tóth, Márton; Theisel, Holger and Wimmer, MichaelSurveillance cameras are expected to work also in bad visibility conditions, which requires algorithmic solutions to improve the captured image and to eliminate image degradation caused by these weather conditions. Algorithms for such tasks belong to the field of computational photography and have been successful in eliminating haze, fog, motion blur, etc. This paper presents a simple algorithm to suppress rain or snow from single images. The algorithm uses energy minimization, and we propose a novel data term and a Bregman distance based regularization term reflecting the particular properties of precipitation.