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Advanced Monte Carlo methods in Image Synthesis
Vévoda, Petr ; Wilkie, Alexander (advisor)
Monte Carlo (MC) integration is an essential tool in many fields of science. In image synthesis, it has enabled photorealistic rendering results via physically based light trans- port simulation. However, an inherent problem of MC integration is variance causing noise in rendered images. This thesis presents three methods, each taking a different approach to variance reduction in rendering. The first approach focuses on improving the sampling technique. An adaptive solution is proposed for unbiased direct illumination sampling, employing Bayesian regression and a novel statistical model of direct illumination to achieve robustness. This method was integrated into a production renderer, demonstrating both its theoretical soundness and practical utility. The second approach explores the combination of multiple sampling techniques via multiple importance sampling (MIS). Optimal weighting functions are derived, proving to minimize the variance of MIS estimators. The new weights outperform all common heuristics and provide novel design considerations for selecting appropriate sampling tech- niques in integration problems. Finally, the third approach involves pre-computation to handle challenging scenarios effectively. Pre-computed reference images of a clear sky are used to create a high- quality fitted model,...
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Advanced Monte Carlo methods in Image Synthesis
Vévoda, Petr ; Wilkie, Alexander (advisor) ; Eisemann, Elmar (referee) ; Schudeiske, Johannes (referee)
Monte Carlo (MC) integration is an essential tool in many fields of science. In image synthesis, it has enabled photorealistic rendering results via physically based light trans- port simulation. However, an inherent problem of MC integration is variance causing noise in rendered images. This thesis presents three methods, each taking a different approach to variance reduction in rendering. The first approach focuses on improving the sampling technique. An adaptive solution is proposed for unbiased direct illumination sampling, employing Bayesian regression and a novel statistical model of direct illumination to achieve robustness. This method was integrated into a production renderer, demonstrating both its theoretical soundness and practical utility. The second approach explores the combination of multiple sampling techniques via multiple importance sampling (MIS). Optimal weighting functions are derived, proving to minimize the variance of MIS estimators. The new weights outperform all common heuristics and provide novel design considerations for selecting appropriate sampling tech- niques in integration problems. Finally, the third approach involves pre-computation to handle challenging scenarios effectively. Pre-computed reference images of a clear sky are used to create a high- quality fitted model,...
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Appearance matching and fabrication using differentiable material models
Nindel, Thomas Klaus ; Wilkie, Alexander (advisor) ; Chalmers, Alan (referee) ; Magnor, Marcus (referee)
Computing derivatives of code - with code - is one of the key enablers of the machine learning revolution. In computer graphics, automatic differentiation allows to solve in- verse rendering problems. There, parameters such as an objects reflectance, position, or the scattering- and absorption coefficients of a volume, are recovered from one or several input images. In this work, we consider appearance matching and fabrication problems, that can be cast as instances of inverse rendering problems. While gradient-based opti- mization that is enabled by differentiable programs has the potential to yield very good results, it requires proper handling - differentiable rendering is not a shotgun-type prob- lem solver. We discuss both theoretical concepts and the practical implementation of differentiable rendering algorithms, and show how they connect to different appearance matching problems. 1
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Efficient and Expressive Microfacet Models
Atanasov, Asen ; Wilkie, Alexander (advisor) ; Yan, Lingqi (referee) ; Ribardière, Mickaël (referee)
Title: Efficient and Expressive Microfacet Models Author: Asen Atanasov Department: Department of Software and Computer Science Education Supervisor: doc. Dr. Alexander Wilkie, Department of Software and Computer Science Education Abstract: In realistic appearance modeling, rough surfaces that have micro- scopic details are described using so-called microfacet models. These include analytical models that statistically define a physically-based microsurface. Such models are extensively used in practice because they are inexpensive to compute and offer considerable flexibility in terms of appearance control. Also, small but visible surface features can easily be added to them through the use of a normal map. However, there are still areas in which this general type of model can be improved: important features like anisotropy control sometimes lack analytic solutions, and the efficient rendering of normal maps requires accurate and general filtering algorithms. We advance the state of the art with regard to such models in these areas: we derive analytic anisotropic models, reformulate the filtering problem and propose an efficient filtering algorithm based on a novel filtering data structure. Specifically, we derive a general result in microfacet theory: given an arbitrary microsurface defined via standard...
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An Efficient Load-balancing Image Sampler for Path Tracing
Kubíček, Tomáš ; Wilkie, Alexander (advisor) ; Nindel, Thomas Klaus (referee)
In this thesis, we go through the process of improving a research renderer called ART. We focus primarily on the image sampler. We analyse the shortcomings of the stochastic sampler that was present before this thesis was written. Those being the huge memory consumption, lack of real-time visualization, and a limited communication channel between the renderer and the application that is supposed to control it. We then design two samplers that could serve as a replacement. We choose the one which seems to be better suited for the task. We then run a series of tests which serve to finetune parameters of the new sampler and also serve as a comparison between the new and the old sampler. By using the data from the tests we show that we have reduced the memory foot-print while maintaining the speed at mostly the same level as before while enabling working with greater number of cores. 1
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Best View of 3D Scene
Jankovič, Ivan ; Pelikán, Josef (advisor) ; Wilkie, Alexander (referee)
The computation of good viewpoints is useful in many fields: exploration of virtual worlds, global illumination, robot motion, radiosity, imagebased modeling, etc. The main goal of the thesis was to implement several methods for computing the optimal viewpoint of a 3D scene. Two methods have been implemented - Heuristic Measure and Viewpoint Entropy. In addition, a modification of the first method, Weighted Heuristic Measure, was created and tested to find the values that give the best results. For the purpose of method evaluation, a simple application was developed, which loads a 3D scene and runs the implemented methods.
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Procedurální generování měst
Beneš, Jan ; Wilkie, Alexander (advisor) ; Křivánek, Jaroslav (referee)
This thesis proposes a novel method for procedural generation of urban street networks. A simple traffic simulation, based on observations made about the social-geographic nature of cities, that is able to drive the temporal evolution of city road networks by creating new major roads, as well as a modified generation algorithm for minor roads, are described. The presented method is highly automated.
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Wang Tiles for Frequency-Based Synthesis of Ocean Surfaces
Vámošová, Mária ; Wilkie, Alexander (advisor) ; Krajíček, Václav (referee)
Frequency-based ocean synthesis is a class of methods for generating ocean waves in deep water using physically based ocean spectra provided by oceanographic research. The output of these methods is a heightfield which is periodic and can be used to tile a larger area. However, when using a larger number of tiles, a repetition pattern becomes apparent. Wang tiling is a method of tiling the plane non- periodically by using only a small set of input tiles with given constraints. The aim of this thesis is to create a set of Wang Tiles, each of which represents an ocean heightfield synthesised by a frequency- based method, so one can create large ocean scenes without apparent periodicity in the tiling pattern. Powered by TCPDF (www.tcpdf.org)
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Physically-based Cloud Rendering on GPU
Elek, Oskár ; Wilkie, Alexander (advisor) ; Křivánek, Jaroslav (referee)
The rendering of participating media is an interesting and important problem without a simple solution. Yet even among the wide variety of participating media the clouds stand out as an especially difficult case, because of their properties that make their simulation even harder. The work presented in this thesis attempts to provide a solution to this problem, and moreover, to make the proposed method to work in interactive rendering speeds. The main design criteria in designing this method were its physical plausibility and maximal utilization of specific cloud properties which would help to balance the complex nature of clouds. As a result the proposed method builds on the well known photon mapping algorithm, but modifies it in several ways to obtain interactive and temporarily coherent results. This is further helped by designing the method in such a way which allows its implementation on contemporary GPUs, taking advantage of their massively parallel sheer computational power. We implement a prototype of the method in an application that renders a single realistic cloud in interactive framerates, and discuss possible extensions of the proposed technique that would allow its use in various practical industrial applications.
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Acceleration of Ray-Casting for CSG scenes
Zajíček, Petr ; Wilkie, Alexander (advisor) ; Křivánek, Jaroslav (referee)
Ray tracing acceleration methods are usually applied to scenes defined by triangle meshes.These scenes contain a large number of triangles. In contrast, CSG scenes contain orders of magnitude less more complex primitives primitives. In this thesis we will present the Operation KD-tree. This acceleration method applies the KD-tree --- modern acceleration method developed for triangle meshes --- directly to the CSG scene. This is done on the premise, that the huge reduction in primitive count will yield enhanced performance, when rendering a scene using CSG instead of triangle meshes.
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