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Affordable optical measurement methods for predictive rendering
Iser, Tomáš ; Wilkie, Alexander (advisor) ; Gkioulekas, Ioannis (referee) ; Babaei, Vahid (referee)
Predictive rendering, a part of computer graphics, is based on the light transport equation and focuses on accurately predicting the appearance of objects and materials under various conditions. A variety of problems can be formulated as appearance prediction: from generating photorealistic images to enhancing color 3D printing. The accuracy relies on the materials' optical properties, which must either be estimated from first principles, or measured with expensive and sophisticated optical devices. Could we obtain these properties in an efficient and affordable way optimized for predictive rendering? To answer the question, this thesis bridges the boundary between computer graphics and optics. We develop simpler and more affordable methods for measuring optical properties with a focus on color accuracy, thus making predictive rendering more accessible. We aim at two types of materials that are both ubiquitous but usually neglected because of their complex characteristics: translucent materials and fluorescent materials. For each, we present a separate measurement approach that only uses low-cost optical components, yet has a high spectral resolution for color-accurate applications. Our first method is motivated by measuring translucent inks, which is required for accurate full-color 3D-printing algorithms....
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Smooth Minecraft terrain rendering
Hopfer, Eduard ; Iser, Tomáš (advisor) ; Gouder, Darryl (referee)
Interesting terrain is the backbone of any virtual world. To make features like caves, overhangs, and arches possible, we need to capture the internal structure of the terrain. In other words, we need a volumetric terrain model. Minecraft is known for its rich, procedurally generated worlds. Internally, these worlds use a volumetric representation - a 3D grid of voxels. While these blocky worlds look impressive already, continuous terrain is often more desirable. The goal of this thesis is to create a tool that can visualize Minecraft worlds as smooth surfaces. We explore ways of using Minecraft as a source of volumetric terrain data. The smooth scene is created by extracting a field function and polygonizing the implicit surface it defines. The user can adjust the appearance of the smooth scene through several parameters. The application also supports the exploration of the infinite Minecraft worlds in real-time. 1
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Improving probes in dynamic diffuse global illumination
Roháček, Dominik ; Iser, Tomáš (advisor) ; Kahoun, Martin (referee)
For a long time, real-time renderers typically only supported direct illumination. With recent technological advances, such as much faster GPU computations or the RTX plat- form, simulating more accurate global illumination in real time is now possible. This is especially important for rendering indoor scenes in the context of architectural visual- ization, as users can now add and modify illuminants in real time without waiting for a fully path-traced render. In this thesis, we briefly describe the existing real-time solutions and investigate the Dynamic Diffuse Global Illumination technique in detail. We implement the solution to an existing real-time renderer with RTX support. We specifically describe several problems and artefacts that the method has and present our solutions to those. Mainly, we show an improved approach to probe placing and investigate the improvement it provides. We note that our implementation achieves a better visual quality as it avoids highly noticeable artefacts. 1
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Real-Time Visual Inspection of Spool Winding Quality
Hadrava, Jan ; Obdržálek, David (advisor) ; Iser, Tomáš (referee)
Plastic filaments are used in a fastly growing industry of 3D printing using the Fused Filament Fabrication (FFF) method. A poor quality of spool winding can negatively impact the printing process. On the other hand, producing high-quality filament winding is surprisingly difficult to achieve consistently. The thesis proposes a holistic approach to inspect winding quality during the winding process. We suggest tracking reflections of bright visible light. This method seems robust enough to track filament color from black to white and even transparent materials. Furthermore, it is possible to run everything on cheap and widely available Raspberry Pi 4 B with Camera Module v2. The system uses classical computer vision approaches for filtering, segmentation, and inter-frame tracking of individual filament strands between video frames. It was confirmed to be fast enough to process 30 FPS footage directly on the Raspberry Pi in real-time. Additionally, the GUI tool for quick dataset annotation of spool winding images was created along with a small dataset. Both might be useful for the future development of a system, which would predict the quality issues earlier when corrective action can still be carried out to prevent them. 1
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Efficient Sampling of Re-radiation Matrices in Fluorescence-capable Rendering Systems
Hua, Qingqin ; Wilkie, Alexander (advisor) ; Iser, Tomáš (referee)
Fluorescence is a common effect in nature, it re-emits light by absorbing photons, caus- ing a wavelength shift from a shorter wavelength to a longer one. In recent years, there is an increased interest in including fluorescence in physically-based rendering. Fluorescence behavior is properly represented as a re-radiation matrix: for a given input wavelength, this matrix indicates how much energy is re-emitted at all other wavelengths. However, such a 2D representation has a significant memory footprint, especially when a scene con- tains a high number of fluorescent objects or fluorescent textures. This thesis proposes using Gaussian Mixture Domain to model re-radiation, which allows us to significantly reduce the memory footprint. Instead of storing the full matrix, we work with a set of Gaussian parameters that also allow direct importance sampling. When accuracy is a concern, one can still use the re-radiation matrix data and just benefit from impor- tance sampling provided by the Gaussian Mixture. Our method is useful when numerous fluorescent materials are present in a scene, particularly for textures with fluorescent components. 1
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Constrained Spectral Uplifting
Tódová, Lucia ; Wilkie, Alexander (advisor) ; Iser, Tomáš (referee)
Physically-based spectral rendering is becoming increasingly popular in both commercial and academic areas due to its ability to accurately simulate natural phenomena. However, the production of materials defined by their spectral properties is a tedious and expensive process, which makes the utilization of RGB-based assets in spectral renderers a desired feature. To convert RGB values to their spectral representations, a process called spectral uplifting is employed. As the RGB color space is a finite subset of the visible gamut, there exist multiple conversion techniques producing distinct results, which may cause color inconsistencies under various lighting conditions. This thesis proposes a method for constraining the spectral uplifting process. To be specific, pre-defined mappings of RGB values to their spectral representations are preserved and the rest of the RGB gamut is plausibly uplifted. In order to assess its correctness, this technique is then implemented and evaluated in a spectral renderer. The renders uplifted via our method show minimal discrepancies when compared to the original textures.
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Simulace formování obrazu v elektronovém mikroskopu pomocí sledování elektronů
Mikuš, Pavel ; Iser, Tomáš (advisor) ; Vorba, Jiří (referee)
Cryogenic electron microscopy (cryo-EM) is an evolving field allowing molecular visu- alizations with picometer resolutions. Images are acquired by shooting electrons through molecular samples and detecting the scattered electrons. From such data, 3D shapes of the molecules can be inversely reconstructed. Currently, describing and simulating the cryo-EM image formation is based either on naive transmittance models or complicated wave-function formalisms. In this thesis, we explore the possibility of simulating cryo-EM image formation via Monte Carlo electron tracing. We combine a delta-tracking algorithm with an elec- tron elastic differential cross-section function and Rutherford formulae to derive two Monte Carlo estimators. The derived models are implemented in a high-performance C++/CUDA environment and compared with other common models. Our particle-based simulated images show considerable similarity to the wave-based state-of-the-art multi- slice model. We also evaluate our models on class averages of real measurements. Both of our proposed models have significantly higher normalized cross-correlation scores with the measured class averages when compared to the most commonly used transmittance model. The thesis proves the viability of a particle-based Monte Carlo simulation of elec- tron microscope...
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Known-item search in image datasets using simple color sketches
Dräxler, Peter ; Lokoč, Jakub (advisor) ; Iser, Tomáš (referee)
With the growing amount of multimedia content, the availability of quality search tools is becoming increasingly important. Without suitable sample queries, it is difficult to evaluate quality of any search algorithm. In this work we search for a known image in a database. We describe an experiment in which 2,500 simple color drawings were collected from real users. Using these drawings, we evaluate the accuracy with which the user is able to remember the colors in the image. We use the obtained data to evaluate the accuracy of various search models. Part of the work is also a web application that allows you to search in images. 1
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Dimensional measurements from a limited set of X-ray projections
Iser, Tomáš ; Horáček, Jan (advisor) ; Křivánek, Jaroslav (referee)
Modern non-destructive approaches for quality control in manufacturing often rely on X-ray computed tomography to measure even difficult-to-reach features. Unfortunately, such measurements require hundreds or thousands of calibrated X-ray projections, which is a time-consuming process and may cause bottlenecks. In the recent state-of-the-art research, tens and hundreds of projections are still required. In this thesis, we examine the radiography physics, technologies, and ex- isting solutions, and we propose a novel approach for non-destructive dimensional measurements from a limited number of projections. Instead of relying on com- puted tomography, we formulate the measurements as a minimization problem in which we compare our parametric model to reference radiographs. We propose the whole dimensional measurements pipeline, including object parametrizations, material calibrations, simulations, and hierarchical optimizations. We fully im- plemented the method and evaluated its accuracy and repeatability using real radiographs of real physical objects. We achieved accuracy in the range of tens or hundreds of micrometers, which is almost comparable to industrial computed tomography, but we only used two or three reference radiographs. These results are significant for industrial quality control. Acquiring...
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Real-Time Light Transport in Analytically Integrable Participating Media
Iser, Tomáš ; Elek, Oskár (advisor) ; Horáček, Jan (referee)
The focus of this thesis is the real-time rendering of participating media, such as fog. This is an important problem, because such media significantly influence the appearance of the rendered scene. It is also a challenging one, because its physically correct solution involves a costly simulation of a very large number of light-particle interactions, especially when considering multiple scattering. The existing real-time approaches are mostly based on empirical or single-scattering approximations, or only consider homogeneous media. This work briefly examines the existing solutions and then presents an improved method for real-time multi- ple scattering in quasi-heterogeneous media. We use analytically integrable den- sity functions and efficient MIP map filtering with several techniques to minimize the inherent visual artifacts. The solution has been implemented and evaluated in a combined CPU/GPU prototype application. The resulting highly-parallel method achieves good visual fidelity and has a stable computation time of only a few milliseconds per frame.
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