Volume rendering techniques can be powerful tools when visualizing medical data sets. The characteristics of being able to capture 3-D internal structures make the technique attractive. Scanning equipment is producing medical images, with rapidly increasing resolution, resulting in heavily increased size of the data set. Despite the great amount of processing power CPUs deliver, the required precision in image quality can be hard to obtain in real-time rendering. Therefore, it is highly desirable to optimize the rendering process. Modern GPUs possess much more computational power and is available for general purpose programming through high level shading languages. Efficient representations of the data are crucial due to the limited memory provided by the GPU. This thesis describes the theoretical background and the implementation of an approach presented by Patric Ljung, Claes Lundström and Anders Ynnerman at Linköping University. The main objective is to implement a fully working multi-resolution framework with two separate pipelines for pre-processing and real-time rendering, which uses the GPU to visualize large medical data sets.

Šiame darbe nagrinėjama savivaldybių funkcijos, jų grupavimas, savivaldybių biudžetų pajamų ir išlaidų išlyginimo sistema. Analizuojamais klausimais pateikiami statistiniai duomenys. Padarytos išvados ir pateikti pasiūlymai. Baigiamojo darbo temos pasirinkimą nulėmė jos praktinis reikalingumas ir aktualumas. Savivaldybių uždavinys – kuo geriau tenkinti gyventojų materialinius, buitinius, kultūrinius, švietimo ir kitus poreikius. Kiekviena savivaldybė turėtų savo valdomoje ir tvarkomoje teritorijoje gyventojams teikti vienodo lygio, vienodos apimties ir panašios kokybės paslaugas. Aktualu funkcijų pasidalijimas tarp įvairių valdymo lygių ir jų finansavimas. Labai svarbu, perduodant savivaldybėms funkcijas, kartu didinti ir pajamas. Baigiamąjį darbą sudaro 4 dalys, įvadas, išvados ir pasiūlymai, literatūros sąrašas. Pirmoje dalyje išdėstyta savivaldos samprata bei egzistuojantys požiūriai į savivaldybes. Antroje dalyje siekta išaiškinti savivaldybių funkcijas ir jų paskirstymą tarp atskirų valdymo lygių. Išnagrinėta Europos vietos savivaldos chartijos reikšmė savivaldybių finansams. Trečioje dalyje išnagrinėta situacija Lietuvoje nuo jos nepriklausomybės atkūrimo: savivaldybių funkcijų kaita ir skirstymas, svarbiausi teisės aktai, reglamentuojantys savivaldybių funkcijų finansavimą bei pajamų išlyginimą. Išanalizuotos savivaldybių biudžetų pajamos, jų formavimo problemos, o taip pat pateikta valstybinių (perduotų savivaldybėms) funkcijų finansavimo tvarka. Ketvirtoje... [to full text] / This paper analyzes municipal government functions, aggregation, budget revenue and expenditure equalization system. Statistical data pertinent to analyzed issues is presented. Conclusions are drawn and suggestions offered. Principal concepts: public administration, rendering of public services, subsidiarity principal, fiscal decentralization. The subject of the final paper was determined by its practical necessity and relevance. Municipal government tasks – to meet material, daily, cultural, educational and other requirements of the citizens to the best of its ability. Every municipal government in the territory under its control should provide services of equal level and extent and similar quality. Division of functions between various levels of management and its financing is relevant. It is very important to increase revenue when transferring functions to municipal governments. The final paper is made of 4 parts: introduction, conclusions and suggestions, literature used. The first part of the paper states the concept and existing attitudes towards municipal government. The second part strives to ascertain functions of municipal government and their division between different levels of management and studies the importance of European municipal government charter to municipal government financing. In the third part situation in Lithuania since reinstatement of independence has been explored: municipal government function change and distribution, main legislation... [to full text]

In this thesis, luminescence properties of ZnO nanostructures (nanorods, nanotubes, nanowalls and nanoflowers) are investigated by different approaches for possible future application of these nanostructures as white light emitting diodes. ZnO nanostructures were grown by different growth techniques on different p-type substrates. Still it is a challenge for the researchers to produce a stable and reproducible high quality p-type ZnO and this seriously hinders the progress of ZnO homojunction LEDs. Therefore the excellent properties of ZnO can be utilized by constructing heterojunction with other p-type materials. The first part of the thesis includes paper I-IV. In this part, the luminescence properties of ZnO nanorods grown on different p-type substrates (GaN, 4H-SiC) and different ZnO nanostructures (nanorods, nanotubes, nanoflowers, and nanowalls) grown on the same substrate were investigated. The effect of the post-growth annealing of ZnO nanorods and nanotubes on the deep level emissions and color rendering properties were also investigated. In paper I, ZnO nanorods were grown on p-type GaN and 4H-SiC substrates by low temperature aqueous chemical growth (ACG) method. The luminescence properties of the fabricated LEDs were investigated at room temperature by electroluminescence (EL) and photoluminescence (PL) measurements and consistency was found between both the measurements. The LEDs showed very bright emission that was a combination of three emission peaks in the violet-blue, green and orange-red regions in the visible spectrum. In paper II, different ZnO nanostructures (nanorods, nanotubes, nanoflowers, and nanowalls) were grown on p-GaN and the luminescence properties of these nanostructures based LEDs were comparatively investigated by EL and PL measurements. The nanowalls structures were found to be emitting the highest emission in the visible region, while the nanorods have the highest emissions in the UV region due to its good crystal quality. It was also estimated that the ZnO nanowalls structures have strong white light with the highest color rendering index (CRI) of 95 with correlated color temperature (CCT) of 6518 K. In paper III, we have investigated the origin of the red emissions in ZnO by using post-growth annealing. The ZnO nanotubes were achieved on p-GaN and then annealed in different ambients (argon, air, oxygen and nitrogen) at 600 oC for 30 min. By comparative investigations of EL spectra of the LEDs it was found that more than one deep level defects are involved in the red emission from ZnO nanotubes/p-GaN LEDs. It was concluded that the red emission in ZnO can be attributed to oxygen interstitials (Oi) and oxygen vacancies (Vo) in the range of 620 nm (1.99 eV) to 690 nm (1.79 eV) and 690 nm (1.79 eV) to 750 nm (1.65 eV), respectively. In paper IV, we have investigated the effect of post-growth annealing on the color rendering properties of ZnO nanorods based LEDs. ZnO nanorods were grown on p-GaN by using ACG method. The as grown nanorods were annealed in nitrogen, oxygen, argon, and air ambients at 600 oC for 30 min. The color rendering indices (CRIs) and correlated color temperatures (CCTs) were estimated from the spectra emitted by the LEDs. It was found that the annealing ambients especially air, oxygen, and nitrogen were found to be very effective. The LEDs based on nanorods annealed in nitrogen ambient, have excellent color rendering properties with CRIs and CCTs of 97 and 2363 K in the forward bias and 98 and 3157 K in the reverse bias. In the 2nd part of the thesis, the junction temperature of n-ZnO nanorods based LEDs at the built-in potential was modeled and experiments were performed to validate the model. The LEDs were fabricated by ZnO nanorods grown on different p-type substrates (4H-SiC, GaN, and Si) by the ACG method. The model and experimental values of the temperature coefficient of the forward voltage near the built-in potential (~Vo) were compared. It was found that the series resistance has the main contribution in the junction temperature of the fabricated devices. In the 3rd part of the thesis, the influence of helium (He+) ion irradiation bombardment on luminescence properties of ZnO nanorods based LEDs were investigated. ZnO nanorods were grown by the vapor-liquid-solid (VLS) growth method. The fabricated LEDs were irradiated by using 2 MeV He+ ions with fluencies of ~ 2×1013 ions/cm2 and ~ 4×1013 ions/cm2. It was observed that the He+ ions irradiation affects the near band edge emissions as well as the deep level emissions in ZnO. A blue shift about 0.0347 eV and 0.082 eV was observed in the PL spectra in the near band emission and green emission, respectively. EL measurements also showed a blue shift of 0.125 eV in the broad green emission after irradiation. He+ ion irradiation affects the color rendering properties and decreases the color rendering indices from 92 to 89.

Denna rapport beskriver och drar jämförelser mellan olika visualiseringstekniker i 3D Studio Max och Adobe Photoshop CS3. Syftet med studien är att undersöka olika visualiserings- och renderingstekniker för att se vilka tekniker som ger ett smidigast och mest verklighetstroget resultat utifrån olika förutsättningar. Studien grundar sig på en huvudfråga och två stycken underfrågor. Hur skapar man ett effektivt och verklighetstroget visualiseringsresultat av ett bostadskvarter för intressenter? • Vilka fördelar och nackdelar finns det med olika visualiseringstekniker? • Vilka metoder ger ett verklighetstroget visualiseringsresultat vid interiör respektive exteriör visualisering? Slutsatsen med studien är att varje situation är unik och att det finns fördelar och nackdelar med varje teknik och metod i de olika programmen. För att nå ett önskat slutresultat så gäller det att lära sig hur varje metod fungerar och sedan anpassa den utifrån varje enskild situation.

This thesis involves systems for virtual presence in remote locations, a field referred to as telepresence. Recent image-based representations such as Google map's street view provide a familiar example. Several areas of research are open; such image-based representations are huge in size and the necessity to compress data efficiently for storage is inevitable. On the other hand, users are usually located in remote areas, and thus efficient transmission of the visual information is another issue of great importance. In this work, real-world images are used in preference to computer graphics representations, mainly due to the photorealism that they provide as well as to avoid the high computational cost required for simulating large-scale environments. The cubic format is selected for panoramas in this thesis. A major feature of the captured cubic-panoramic image datasets in this work is the assumption of static scenes, and major issues of the system are compression efficiency and random access for storage, as well as computational complexity for transmission upon remote users' requests. First, in order to enable smooth navigation across different view-points, a method for aligning cubic-panorama image datasets by using the geometry of the scene is proposed and tested. Feature detection and camera calibration are incorporated and unlike the existing method, which is limited to a pair of panoramas, our approach is applicable to datasets with a large number of panoramic images, with no need for extra numerical estimation. Second, the problem of cubic-panorama image dataset compression is addressed in a number of ways. Two state-of-the-art approaches, namely the standardized scheme of H.264 and a wavelet-based codec named Dirac, are used and compared for the application of virtual navigation in image based representations of real world environments. Different frame prediction structures and group of pictures lengths are investigated and compared for this new type of visual data. At this stage, based on the obtained results, an efficient prediction structure and bitstream syntax using features of the data as well as satisfying major requirements of the system are proposed. Third, we have proposed novel methods to address the important issue of disparity estimation. A client-server based scheme is assumed and a remote user is assumed to seek information at each navigation step. Considering the compression stage, a fast method that uses our previous work on the geometry of the scene as well as the proposed prediction structure together with the cubic format of panoramas is used to estimate disparity vectors efficiently. Considering the transmission stage, a new transcoding scheme is introduced and a number of different frame-format conversion scenarios are addressed towards the goal of free navigation. Different types of navigation scenarios including forward or backward navigation, as well as user pan, tilt, and zoom are addressed. In all the aforementioned cases, results are compared both visually through error images and videos as well as using the objective measures. Altogether free navigation within the captured panoramic image datasets will be facilitated using our work and it can be incorporated in state-of-the-art of emerging cubic-panorama image dataset compression/transmission schemes.

In applications such as architecture, early design sketches containing accurate line drawings often mislead the target audience [Schumann et al. 1996]. Approximate human-drawn sketches are typically accepted as a better way of demonstrating fundamental design concepts. To this end I have designed an algorithm that creates lines that perceptually resemble human-drawn lines. My algorithm works directly with input point data and a physically–based mathematical model of human arm movement. Further, the algorithm does not rely on a database of human drawn lines, nor does it require any input other than the end points of the lines to generate a line of arbitrary length. The algorithm will generate any number of aesthetically pleasing and natural looking lines, where each one is unique. The algorithm was developed by conducting various user studies on human drawn pencil line sketches, and analyzing the lines to produce basic heuristics. I found that an observational analysis of human lines made a bigger impact on the algorithm than a statistical analysis. A further study shows that the algorithm produces lines that are perceptually indistinguishable from straight hand-drawn pencil lines.

This thesis presents a spatial sound rendering system for the use in immersive virtual environments. Spatial sound rendering aims at artificially reproducing the acoustics of a space. It has many applications such as music production, movies, electronic gaming and teleconferencing. Conventionally, spatial sound rendering is implemented by digital signal processing algorithms derived from perceptual models or simplified physical models. While being flexible and/or efficient, these models are not able to capture the acoustical impression of a space faithfully. On the other side, convolving the sound sources with properly measured impulse responses produces the highest possible fidelity, but it is not practically useful for many applications because one impulse response corresponds to one source/listener configuration so that the sources or the listeners can not be relocated. In this thesis, techniques for measuring multichannel room impulse responses (MMRIR) are reviewed. Then, methods for analyzing measured MMRIR and rendering virtual acoustical environment based on such analysis are presented and evaluated. The analysis can be performed off-line. During this stage, a set of filters that represent the characteristics of the air and walls inside the acoustic space are obtained. Based on the assumption that the MMRIR acquired at one "good" position in the target space can be used to simulate the late reverb at other positions in the same space, appropriate segments that can be used as reverb tails are extracted from the measured MMRIR. The rendering system first constructs an early reflection model based on the positions of the listener-source pair and the filters derived, then combines with the late reverb segments to form a complete listener-source-room acoustical model that can be used to synthesize high quality multi-channel audio for arbitrary listener-source positions. Another merit of the proposed framework is that it is scalable. At the expense of slightly degraded rendering quality, the computational complexity can be greatly reduced. This makes this framework suitable for a wide range of applications that have different quality and complexity requirements. The proposed framework has been evaluated by formal listening tests. These tests have proven the effectiveness in preserving the spatial quality while positioning the listener-source pair accurately, as well as justified the key assumptions made by the proposed system.

The creation of expressive styles for digital art is one of the primary goals in non-photorealistic rendering. In this paper, we introduce a swarm-based multi-agent system that is capable of producing expressive imagery through the use of multiple digital images. At birth, agents in our system are assigned a digital image that represents their 'aesthetic ideal'. As agents move throughout a digital canvas they try to 'realize' their ideal by modifying the pixels in the digital canvas to be closer to the pixels in their aesthetic ideal. When groups of agents with different aesthetic ideals occupy the same canvas, a new image is created through the convergence of their competing aesthetic goals. We use our system to explore the concepts and techniques from a number of Modern Art movements and to create an interactive media installation. The simple implementation and effective results produced by our system makes a compelling argument for more research using swarm-based multi-agent systems for non-photorealistic rendering. / Graduate

This thesis proposes an efficient method to accelerate ray based volume rendering with texture slabs using programmable graphics hardware. In this method, empty space skipping and early ray termination are utilized without performing any preprocessing on CPU side. The acceleration structure is created on the fly by making use of depth buffer efficiently on Graphics Processing Unit (GPU) side. In the proposed method, texture slices are grouped together to form a texture slab. Rendering all the slabs from front to back viewing order in multiple rendering passes generates the resulting volume image. Slab silhouette maps (SSM) are created to identify and skip empty spaces along the ray direction at pixel level. These maps are created from the alpha component of the slab and stored in the depth buffer. In addition to the empty region information, SSM also contains information about the terminated rays. The method relies on hardware z-occlusion culling that is realized by means of SSMs to accelerate ray traversals. The cost of generating this acceleration data structure is very small compared to the total rendering time.

Zugl.: Wuppertal, Univ., Diss., 2005