Practical surface light fields

The rendering of photorealistic surface appearance is one of the main challenges facing modern computer graphics. Image-based approaches have become increasingly important because they can capture the appearance of a wide variety of physical surfaces with complex reflectance behavior. In this dissertation, I focus on surface light fields, an image-based representation of view-dependent and spatially-varying appearance. Constructing a surface light field can be a time-consuming and tedious process. The data sizes are quite large, often requiring multiple gigabytes to represent complex reflectance properties. The result can only be viewed after a lengthy post-process is complete, so it can be difficult to determine when the light field is sufficiently sampled. Often, uncertainty about the sampling density leads users to capture many more images than necessary in order to guarantee adequate coverage. To address these problems, I present several approaches to simplify the capture of surface light fields. The first is a “human-in-the-loop” interactive feedback system based on the online svd. As each image is captured, it is incorporated into the representation in a streaming fashion and displayed to the user. In this way, the user receives direct feedback about the capture process, and can use this feedback to improve the sampling. To avoid the problems of discretization and resampling, I used incremental weighted least squares, a subset of radial basis function which allows for incremental local construction and fast rendering on graphics hardware. Lastly, I address the limitation of fixed lighting by describing a system that captures the surface light field of an object under synthetic lighting

Efficient Acoustic Simulation for Immersive Media and Digital Fabrication

Sound is a crucial part of our life. Well-designed acoustic behaviors can lead to significant improvement in both physical and virtual interactions. In computer graphics, most existing methods focused primarily on improving the accuracy. It remained underexplored on how to develop efficient acoustic simulation algorithms for interactive practical applications. The challenges arise from the dilemma between expensive accurate simulations and fast feedback demanded by intuitive user interaction: traditional physics-based acoustic simulations are computationally expensive; yet, for end users to benefit from the simulations, it is crucial to give prompt feedback during interactions. In this thesis, I investigate how to develop efficient acoustic simulations for real-world applications such as immersive media and digital fabrication. To address the above-mentioned challenges, I leverage precomputation and optimization to significantly improve the speed while preserving the accuracy of complex acoustic phenomena. This work discusses three efforts along this research direction: First, to ease sound designer's workflow, we developed a fast keypoint-based precomputation algorithm to enable interactive acoustic transfer values in virtual sound simulations. Second, for realistic audio editing in 360° videos, we proposed an inverse material optimization based on fast sound simulation and a hybrid ambisonic audio synthesis that exploits the directional isotropy in spatial audios. Third, we devised a modular approach to efficiently simulate and optimize fabrication-ready acoustic filters, achieving orders of magnitudes speedup while maintaining the simulation accuracy. Through this series of projects, I demonstrate a wide range of applications made possible by efficient acoustic simulations

The Third International Symposium on Space Terahertz Technology: Symposium proceedings

Papers from the symposium are presented that are relevant to the generation, detection, and use of the terahertz spectral region for space astronomy and remote sensing of the Earth's upper atmosphere. The program included thirteen sessions covering a wide variety of topics including solid-state oscillators, power-combining techniques, mixers, harmonic multipliers, antennas and antenna arrays, submillimeter receivers, and measurement techniques

Instrumentation of CdZnTe detectors for measuring prompt gamma-rays emitted during particle therapy

Background: The irradiation of cancer patients with charged particles, mainly protons and carbon ions, has become an established method for the treatment of specific types of tumors. In comparison with the use of X-rays or gamma-rays, particle therapy has the advantage that the dose distribution in the patient can be precisely controlled. Tissue or organs lying near the tumor will be spared. A verification of the treatment plan with the actual dose deposition by means of a measurement can be done through range assessment of the particle beam. For this purpose, prompt gamma-rays are detected, which are emitted by the affected target volume during irradiation. Motivation: The detection of prompt gamma-rays is a task related to radiation detection and measurement. Nuclear applications in medicine can be found in particular for in vivo diagnosis. In that respect the spatially resolved measurement of gamma-rays is an essential technique for nuclear imaging, however, technical requirements of radiation measurement during particle therapy are much more challenging than those of classical applications. For this purpose, appropriate instruments beyond the state-of-the-art need to be developed and tested for detecting prompt gamma-rays. Hence the success of a method for range assessment of particle beams is largely determined by the implementation of electronics. In practice, this means that a suitable detector material with adapted readout electronics, signal and information processing, and data interface must be utilized to solve the challenges. Thus, the parameters of the system (e.g. segmentation, time or energy resolution) can be optimized depending on the method (e.g. slit camera, time-of-flight measurement or Compton camera). Regardless of the method, the detector system must have a high count rate capability and a large measuring range (>7 MeV). For a subsequent evaluation of a suitable method for imaging, the mentioned parameters may not be restricted by the electronics. Digital signal processing is predestined for multipurpose tasks, and, in terms of the demands made, the performance of such an implementation has to be determined. Materials and methods: In this study, the instrumentation of a detector system for prompt gamma-rays emitted during particle therapy is limited to the use of a cadmium zinc telluride (CdZnTe, CZT) semiconductor detector. The detector crystal is divided into an 8x8 pixel array by segmented electrodes. Analog and digital signal processing are exemplarily tested with this type of detector and aims for application of a Compton camera to range assessment. The electronics are implemented with commercial off-the-shelf (COTS) components. If applicable, functional units of the detector system were digitalized and implemented in a field-programmable gate array (FPGA). An efficient implementation of the algorithms in terms of timing and logic utilization is fundamental to the design of digital circuits. The measurement system is characterized with radioactive sources to determine the measurement dynamic range and resolution. Finally, the performance is examined in terms of the requirements of particle therapy with experiments at particle accelerators. Results: A detector system based on a CZT pixel detector has been developed and tested. Although the use of an application-specific integrated circuit is convenient, this approach was rejected because there was no circuit available which met the requirements. Instead, a multichannel, compact, and low-noise analog amplifier circuit with COTS components has been implemented. Finally, the 65 information channels of a detector are digitized, processed and visualized. An advanced digital signal processing transforms the traditional approaches of nuclear electronics in algorithms and digital filter structures for an FPGA. With regard to the characteristic signals (e.g. varying rise times, depth-dependent energy measurement) of a CZT pixel detector, it could be shown that digital pulse processing results in a very good energy resolution (~2% FWHM at 511 keV), as well as permits a time measurement in the range of some tens of nanoseconds. Furthermore, the experimental results have shown that the dynamic range of the detector system could be significantly improved compared to the existing prototype of the Compton camera (~10 keV..7 MeV). Even count rates of ~100 kcps in a high-energy beam could be ultimately processed with the CZT pixel detector. But this is merely a limit of the detector due to its volume, and not related to electronics. In addition, the versatility of digital signal processing has been demonstrated with other detector materials (e.g. CeBr3). With foresight on high data throughput in a distributed data acquisition from multiple detectors, a Gigabit Ethernet link has been implemented as data interface. Conclusions: To fully exploit the capabilities of a CZT pixel detector, a digital signal processing is absolutely necessary. A decisive advantage of the digital approach is the ease of use in a multichannel system. Thus with digitalization, a necessary step has been done to master the complexity of a Compton camera. Furthermore, the benchmark of technology shows that a CZT pixel detector withstands the requirements of measuring prompt gamma-rays during particle therapy. The previously used orthogonal strip detector must be replaced by the pixel detector in favor of increased efficiency and improved energy resolution. With the integration of the developed digital detector system into a Compton camera, it must be ultimately proven whether this method is applicable for range assessment in particle therapy. Even if another method is more convenient in a clinical environment due to practical considerations, the detector system of that method may benefit from the shown instrumentation of a digital signal processing system for nuclear applications.:1. Introduction 1.1. Aim of this work 2. Analog front-end electronics 2.1. State-of-the-art 2.2. Basic design considerations 2.2.1. CZT detector assembly 2.2.2. Electrical characteristics of a CZT pixel detector 2.2.3. High voltage biasing and grounding 2.2.4. Signal formation in CZT detectors 2.2.5. Readout concepts 2.2.6. Operational amplifier 2.3. Circuit design of a charge-sensitive amplifier 2.3.1. Circuit analysis 2.3.2. Charge-to-voltage transfer function 2.3.3. Input coupling of the CSA 2.3.4. Noise 2.4. Implementation and Test 2.5. Results 2.5.1. Test pulse input 2.5.2. Pixel detector 2.6. Conclusion 3. Digital signal processing 3.1. Unfolding-synthesis technique 3.2. Digital deconvolution 3.2.1. Prior work 3.2.2. Discrete-time inverse amplifier transfer function 3.2.3. Application to measured signals 3.2.4. Implementation of a higher order IIR filter 3.2.5. Conclusion 3.3. Digital pulse synthesis 3.3.1. Prior work 3.3.2. FIR filter structures for FPGAs 3.3.3. Optimized fixed-point arithmetic 3.3.4. Conclusion 4. Data interface 4.1. State-of-the-art 4.2. Embedded Gigabit Ethernet protocol stack 4.3. Implementation 4.3.1. System overview 4.3.2. Media Access Control 4.3.3. Embedded protocol stack 4.3.4. Clock synchronization 4.4. Measurements and results 4.4.1. Throughput performance 4.4.2. Synchronization 4.4.3. Resource utilization 4.5. Conclusion 5. Experimental results 5.1. Digital pulse shapers 5.1.1. Spectroscopy application 5.1.2. Timing applications 5.2. Gamma-ray spectroscopy 5.2.1. Energy resolution of scintillation detectors 5.2.2. Energy resolution of a CZT pixel detector 5.3. Gamma-ray timing 5.3.1. Timing performance of scintillation detectors 5.3.2. Timing performance of CZT pixel detectors 5.4. Measurements with a particle beam 5.4.1. Bremsstrahlung Facility at ELBE 6. Discussion 7. Summary 8. ZusammenfassungHintergrund: Die Bestrahlung von Krebspatienten mit geladenen Teilchen, vor allem Protonen oder Kohlenstoffionen, ist mittlerweile eine etablierte Methode zur Behandlung von speziellen Tumorarten. Im Vergleich mit der Anwendung von Röntgen- oder Gammastrahlen hat die Teilchentherapie den Vorteil, dass die Dosisverteilung im Patienten präziser gesteuert werden kann. Dadurch werden um den Tumor liegendes Gewebe oder Organe geschont. Die messtechnische Verifikation des Bestrahlungsplans mit der tatsächlichen Dosisdeposition kann über eine Reichweitenkontrolle des Teilchenstrahls erfolgen. Für diesen Zweck werden prompte Gammastrahlen detektiert, die während der Bestrahlung vom getroffenen Zielvolumen emittiert werden. Fragestellung: Die Detektion von prompten Gammastrahlen ist eine Aufgabenstellung der Strahlenmesstechnik. Strahlenanwendungen in der Medizintechnik finden sich insbesondere in der in-vivo Diagnostik. Dabei ist die räumlich aufgelöste Messung von Gammastrahlen bereits zentraler Bestandteil der nuklearmedizinischen Bildgebung, jedoch sind die technischen Anforderungen der Strahlendetektion während der Teilchentherapie im Vergleich mit klassischen Anwendungen weitaus anspruchsvoller. Über den Stand der Technik hinaus müssen für diesen Zweck geeignete Instrumente zur Erfassung der prompten Gammastrahlen entwickelt und erprobt werden. Die elektrotechnische Realisierung bestimmt maßgeblich den Erfolg eines Verfahrens zur Reichweitenkontrolle von Teilchenstrahlen. Konkret bedeutet dies, dass ein geeignetes Detektormaterial mit angepasster Ausleseelektronik, Signal- und Informationsverarbeitung sowie Datenschnittstelle zur Problemlösung eingesetzt werden muss. Damit können die Parameter des Systems (z. B. Segmentierung, Zeit- oder Energieauflösung) in Abhängigkeit der Methode (z.B. Schlitzkamera, Flugzeitmessung oder Compton-Kamera) optimiert werden. Unabhängig vom Verfahren muss das Detektorsystem eine hohe Ratenfestigkeit und einen großen Messbereich (>7 MeV) besitzen. Für die anschließende Evaluierung eines geeigneten Verfahrens zur Bildgebung dürfen die genannten Parameter durch die Elektronik nicht eingeschränkt werden. Eine digitale Signalverarbeitung ist für universelle Aufgaben prädestiniert und die Leistungsfähigkeit einer solchen Implementierung soll hinsichtlich der gestellten Anforderungen bestimmt werden. Material und Methode: Die Instrumentierung eines Detektorsystems für prompte Gammastrahlen beschränkt sich in dieser Arbeit auf die Anwendung eines Cadmiumzinktellurid (CdZnTe, CZT) Halbleiterdetektors. Der Detektorkristall ist durch segmentierte Elektroden in ein 8x8 Pixelarray geteilt. Die analoge und digitale Signalverarbeitung wird beispielhaft mit diesem Detektortyp erprobt und zielt auf die Anwendung zur Reichweitenkontrolle mit einer Compton-Kamera. Die Elektronik wird mit seriengefertigten integrierten Schaltkreisen umgesetzt. Soweit möglich, werden die Funktionseinheiten des Detektorsystems digitalisiert und in einem field-programmable gate array (FPGA) implementiert. Eine effiziente Umsetzung der Algorithmen in Bezug auf Zeitverhalten und Logikverbrauch ist grundlegend für den Entwurf der digitalen Schaltungen. Das Messsystem wird mit radioaktiven Prüfstrahlern hinsichtlich Messbereichsdynamik und Auflösung charakterisiert. Schließlich wird die Leistungsfähigkeit hinsichtlich der Anforderungen der Teilchentherapie mit Experimenten am Teilchenbeschleuniger untersucht. Ergebnisse: Es wurde ein Detektorsystem auf Basis von CZT Pixeldetektoren entwickelt und erprobt. Obwohl der Einsatz einer anwendungsspezifischen integrierten Schaltung zweckmäßig wäre, wurde dieser Ansatz zurückgewiesen, da kein verfügbarer Schaltkreis die Anforderungen erfüllte. Stattdessen wurde eine vielkanalige, kompakte und rauscharme analoge Verstärkerschaltung mit seriengefertigten integrierten Schaltkreisen aufgebaut. Letztendlich werden die 65 Informationskanäle eines Detektors digitalisiert, verarbeitet und visualisiert. Eine fortschrittliche digitale Signalverarbeitung überführt die traditionellen Ansätze der Nuklearelektronik in Algorithmen und digitale Filterstrukturen für einen FPGA. Es konnte gezeigt werden, dass die digitale Pulsverarbeitung in Bezug auf die charakteristischen Signale (u.a. variierende Anstiegszeiten, tiefenabhängige Energiemessung) eines CZT Pixeldetektors eine sehr gute Energieauflösung (~2% FWHM at 511 keV) sowie eine Zeitmessung im Bereich von einigen 10 ns ermöglicht. Weiterhin haben die experimentellen Ergebnisse gezeigt, dass der Dynamikbereich des Detektorsystems im Vergleich zum bestehenden Prototyp der Compton-Kamera deutlich verbessert werden konnte (~10 keV..7 MeV). Nach allem konnten auch Zählraten von >100 kcps in einem hochenergetischen Strahl mit dem CZT Pixeldetektor verarbeitet werden. Dies stellt aber lediglich eine Begrenzung des Detektors aufgrund seines Volumens, nicht jedoch der Elektronik, dar. Zudem wurde die Vielseitigkeit der digitalen Signalverarbeitung auch mit anderen Detektormaterialen (u.a. CeBr3) demonstriert. Mit Voraussicht auf einen hohen Datendurchsatz in einer verteilten Datenerfassung von mehreren Detektoren, wurde als Datenschnittstelle eine Gigabit Ethernet Verbindung implementiert. Schlussfolgerung: Um die Leistungsfähigkeit eines CZT Pixeldetektors vollständig auszunutzen, ist eine digitale Signalverarbeitung zwingend notwendig. Ein entscheidender Vorteil des digitalen Ansatzes ist die einfache Handhabbarkeit in einem vielkanaligen System. Mit der Digitalisierung wurde ein notwendiger Schritt getan, um die Komplexität einer Compton-Kamera beherrschbar zu machen. Weiterhin zeigt die Technologiebewertung, dass ein CZT Pixeldetektor den Anforderungen der Teilchentherapie für die Messung prompter Gammastrahlen stand hält. Der bisher eingesetzte Streifendetektor muss zugunsten einer gesteigerten Effizienz und verbesserter Energieauflösung durch den Pixeldetektor ersetzt werden. Mit der Integration des entwickelten digitalen Detektorsystems in eine Compton-Kamera muss abschließend geprüft werden, ob dieses Verfahren für die Reichweitenkontrolle in der Teilchentherapie anwendbar ist. Auch wenn sich herausstellt, dass ein anderes Verfahren unter klinischen Bedingungen praktikabler ist, so kann auch dieses Detektorsystem von der gezeigten Instrumentierung eines digitalen Signalverarbeitungssystems profitieren.:1. Introduction 1.1. Aim of this work 2. Analog front-end electronics 2.1. State-of-the-art 2.2. Basic design considerations 2.2.1. CZT detector assembly 2.2.2. Electrical characteristics of a CZT pixel detector 2.2.3. High voltage biasing and grounding 2.2.4. Signal formation in CZT detectors 2.2.5. Readout concepts 2.2.6. Operational amplifier 2.3. Circuit design of a charge-sensitive amplifier 2.3.1. Circuit analysis 2.3.2. Charge-to-voltage transfer function 2.3.3. Input coupling of the CSA 2.3.4. Noise 2.4. Implementation and Test 2.5. Results 2.5.1. Test pulse input 2.5.2. Pixel detector 2.6. Conclusion 3. Digital signal processing 3.1. Unfolding-synthesis technique 3.2. Digital deconvolution 3.2.1. Prior work 3.2.2. Discrete-time inverse amplifier transfer function 3.2.3. Application to measured signals 3.2.4. Implementation of a higher order IIR filter 3.2.5. Conclusion 3.3. Digital pulse synthesis 3.3.1. Prior work 3.3.2. FIR filter structures for FPGAs 3.3.3. Optimized fixed-point arithmetic 3.3.4. Conclusion 4. Data interface 4.1. State-of-the-art 4.2. Embedded Gigabit Ethernet protocol stack 4.3. Implementation 4.3.1. System overview 4.3.2. Media Access Control 4.3.3. Embedded protocol stack 4.3.4. Clock synchronization 4.4. Measurements and results 4.4.1. Throughput performance 4.4.2. Synchronization 4.4.3. Resource utilization 4.5. Conclusion 5. Experimental results 5.1. Digital pulse shapers 5.1.1. Spectroscopy application 5.1.2. Timing applications 5.2. Gamma-ray spectroscopy 5.2.1. Energy resolution of scintillation detectors 5.2.2. Energy resolution of a CZT pixel detector 5.3. Gamma-ray timing 5.3.1. Timing performance of scintillation detectors 5.3.2. Timing performance of CZT pixel detectors 5.4. Measurements with a particle beam 5.4.1. Bremsstrahlung Facility at ELBE 6. Discussion 7. Summary 8. Zusammenfassun

Mathematical techniques for shape modelling in computer graphics: A distance-based approach.

This research is concerned with shape modelling in computer graphics. The dissertation provides a review of the main research topics and developments in shape modelling and discusses current visualisation techniques required for the display of the models produced. In computer graphics surfaces are normally defined using analytic functions. Geometry however, supplies many shapes without providing their analytic descriptions. These are defined implicitly through fundamental relationships between primitive geometrical objects. Transferring this approach in computer graphics, opens new directions in shape modelling by enabling the definition of new objects or supplying a rigorous alternative to analytical definitions of objects with complex analytical descriptions. We review, in this dissertation, relevant works in the area of implicit modelling. Based on our observations on the shortcomings of these works, we develop an implicit modelling approach which draws on a seminal technique in this area: the distance based object definition. We investigate the principles, potential and applications of this technique both in conceptual terms (modelling aspects) and on technical merit (visualisation issues). This is the context of this PhD research. The conceptual and technological frameworks developed are presented in terms of a comprehensive investigation of an object's constituent primitives and modelling constraints on the one hand, and software visualisation platforms on the other. Finally, we adopt a critical perspective of our work to discuss possible directions for further improvements and exploitation for the modelling approach we have developed

Sketching for Real-time Control of Crowd Simulations

Controlling the behaviour of a crowd simulation typically involves tuning of a system's parameters through trial and error, a time-consuming process relying on knowledge of a potentially complex parameter set. Numerous graphical control approaches have been proposed to allow the user to interact with a simulation intuitively. This research investigates the use of a real-time sketch-based approach for crowd simulation control. This is done by modifying the environment of the simulation. Users can create entrances/exits, barriers and flow lines in real-time on top of an environment. This process requires a data structure to represent the environment and navigate the crowd through it. Two alternatives are presented: grid and navigation mesh. A detailed comparison shows that the navigation mesh is a more scalable approach since it uses less memory, has a similar pathfinding time, and is a better structure to represent the environment than the grid. The thesis also presents extensions to the sketch-based approach in the form of novel control tools, including storyboards to define the journey of the crowd, a timeline interface to simulate events through the day, and a sketch-based group storyboard to link behaviours and paths to be followed by a group. These tools are used to create two complex scenarios to exemplify possible applications of the sketch-based approach. The work on timelines also raises a new problem for an approach that dynamically modifies an environment in real-time which is 'when does the crowd know about the change?' Some initial solutions to how this should be handled are presented. The sketch-based system is evaluated by comparing it to a validated commercial system called MassMotion. The comparison takes into account the plausibility of the simulation and usability of the user interface. A user study is carried out to evaluate the graphical user interface of both systems. Formal evaluation methods are used to make the comparison: the benchmark suite 'steersuite', an adapted version of the Keystroke-Level Model (KLM) and the System Usability Scale (SUS). The results show that the sketch-based approach is faster and easier to use than MassMotion, but with fewer control options. An implementation of the sketching interface in a Virtual Reality environment is also considered. However, when compared to the desktop interface using a proposed adaptation to KLM for VR, the results show that sketching in a VR environment is slower and less accurate than the desktop version

AI-generated Content for Various Data Modalities: A Survey

AI-generated content (AIGC) methods aim to produce text, images, videos, 3D assets, and other media using AI algorithms. Due to its wide range of applications and the demonstrated potential of recent works, AIGC developments have been attracting lots of attention recently, and AIGC methods have been developed for various data modalities, such as image, video, text, 3D shape (as voxels, point clouds, meshes, and neural implicit fields), 3D scene, 3D human avatar (body and head), 3D motion, and audio -- each presenting different characteristics and challenges. Furthermore, there have also been many significant developments in cross-modality AIGC methods, where generative methods can receive conditioning input in one modality and produce outputs in another. Examples include going from various modalities to image, video, 3D shape, 3D scene, 3D avatar (body and head), 3D motion (skeleton and avatar), and audio modalities. In this paper, we provide a comprehensive review of AIGC methods across different data modalities, including both single-modality and cross-modality methods, highlighting the various challenges, representative works, and recent technical directions in each setting. We also survey the representative datasets throughout the modalities, and present comparative results for various modalities. Moreover, we also discuss the challenges and potential future research directions