Previous research from environmental psychology shows that human well-being suffers in windowless environments in many ways and a window view of nature is psychologically and physiologically beneficial to humans. Current window substitutes, still images and video, lack three dimensional properties necessary for a realistic viewing experience – primarily motion parallax. We present a new system using a head-coupled display and image-based rendering to simulate a photorealistic artificial window view of nature with motion parallax. Evaluation data obtained from human subjects suggest that the system prototype is a better window substitute than a static image and has significantly more positive effects on observers’ moods. The test subjects judged the system prototype as a good simulation of, and acceptable replacement for, a real window, and accorded it much higher ratings for realism and preference than a static image.

Virtual crowd rendering have been used in film industry with offine rendering methods for a long time. But its existence in interactive real-time applications such as video games is not so common due to the limited rendering power of current graphics hardware. This thesis describes a novel method to improve shadow mapping performance of a crowded scene by taking into account the screen space visibility of the casted shadow of a crowd instance when rendering the shadow maps. A grid-based visibility mask creation method is proposed which is irrelevant to scene complexity. This improves the rendering performance especially when there are many occluded instances of the crowd which is a common scenario in urban environments and accelerates the usage of crowds in real time applications, such as games. We compute visibility of all agents in a crowd in parallel on the graphics processing unit(GPU) without having a requirement of a stencil buer or light direction dependent shadow mask. Technique also improves the view space rendering time by reducing the visibility check cost of the agents that are located on the invisible areas of the scene. The methodology introduced in this thesis gets more effective in each shadow map rendering pass by re-using the same visibility mask for shadow caster culling and enables many local lights with shadows. We also give a brief information about the state of the art of crowd rendering and shadowing, explaining how suitable the method with the implementations of different shadow mapping approaches. The technique is very well compatible with the modern crowd rendering techniques such as skinned instancing, dynamic level of detail(LOD) determination and GPU-based simulation.

Visualizing and manipulating volumetric data is a major component in many areas including anatomical registration in biomedical fields, seismic data analysis in the oil industry, machine part design in computer-aided geometric design, character animation in the movie industry, and fluid simulation. These industries have to meet the demands of the times and be able to make meaningful assertions about the data they generate. The shear size of this data presents many challenges to facilitating realtime interaction. In the recent decade, graphics hardware has become increasingly powerful and more sophisticated which has introduced a new realm of possibilities for processing volumetric data. This thesis focuses on a suite of techniques for viewing and editing volumetric data that efficiently use the processing power of central processing units (CPUs) as well as the large processing power of the graphics hardware (GPUs). This work begins with an algorithm to improve the efficiency of a texture-based volume rendering. We continue with a framework for performing realtime constructive solid geometry (CSG) with complex shapes and smoothing operations on watertight meshes based on a variation of Depth Peeling. We then move to an intuitive technique for deforming volumetric data using a collection of control points. Finally, we apply this technique to image registration of 3-dimensional computed tomography (CT) images used for lung cancel treatment, planning.

University of Macau / Faculty of Science and Technology / Department of Computer and Information Science

A solar fiber optic lighting system, SP3 from the Swedish company Parans Solar Lighting AB, has been installed in a study area/corridor test site. A collector is tracking the sun during daytime, focusing the direct sun irradiance via Fresnel lenses into optical fibers, which guide the solar light into the building. The illumination properties of the system have been characterized. The energy saving due to reduced need of artificial lighting have been calculated and methods for balancing the artificial lights in the test site have been evaluated. The illumination at the test site using solar light was at least as high as when using the artificial lights and even higher at very clear days. The luminous flux output (500 lm) was somewhat lower than specified by the manufacturer (550 lm) at 100 000 lx direct sun illuminance. The output at 130 000 lx was high 767±33 lm the sunlight coupling efficiency 23 %. However, for a 20 m SP3 system the luminous flux output (400 lm) at 100 000 lx was higher than specified (350 lm). The SP3 system of Parans provides high quality solar light. It has a fuller spectrum close to the spectrum of the sun compared to the fluorescent lights at the test site. The correlated color temperature of the system was 5800±300 K and the color rendering index 84.9±0.5. The lighting energy saved due to decreased need for artificial light was estimated to 19 % in Uppsala which has 1790 annual sun hours. The savings in Italy, which has 3400 sun hours, is 46 %. Additional saving, especially in warmer countries can be obtained due to decreased need for cooling in the building as the solar luminaires provide negligible heat to the indoor air. Economical saving could also be realized by improved well-being of the occupants spending time under the solar luminaires. Three ways of balancing the artificial light due to sunshine fluctuations have been investigated. The global horizontal irradiance could not be used as a control signal for balancing the artificial lights but a pyranometer attached to the SP3 sun tracking collector was usable. Also the signal from an indoor luxmeter sensor could be used for balancing the light. However the signal from the light sensor which makes the SP3 collector to track the sun is probably the most cost effective method as it would serve two purposes; tracking the sun and balancing the artificial lights.

The objective of this thesis is the development of algorithms for the simulation of the light transport in general environments to render high quality still images. To this end, first we have analyzed the existing methods able to render participating media, more concretely those that account for multiple scattering within the media. Next, we have devised a couple of two pass methods for the computation of those images. For the first step we have proposed algorithms to cope with the scenes we want to deal with. The second step uses the coarse solution of the first step to obtain the final rendered image.The structure of the dissertation is briefly presented below.In the first chapter the motivation of the thesis and its objectives are discussed. It also summarizes the contributions of the thesis and its organization.In the second chapter the principles of global illumination for general environments are reviewed, with the most important equations---the rendering equation and the transport equation---whose solution constitutes the global illumination problem. In order to solve the global illumination problem, a certain number of multi-pass methods exist. Their objective is to be able to skip restrictions on the number of types of light paths that could be dealt with a single technique, or increase efficiency and/or accuracy. We have opted to follow this philosophy, and a pair of two pass methods have been developed for general environments.The third chapter includes the study of the methods that perform the single scattering approximation, and also the study of the ones that take into account multiple scattering.The fourth chapter is devoted to our first pass method, which computes a rough estimate of the global illumination. Knowing the benefits of hierarchical approaches, two concrete algorithms based on hierarchies have been extended to be more generic: Hierarchical Radiosity with Clustering and Hierarchical Monte Carlo Radiosity.Our second pass is considered in the next chapter. Using the coarse solution obtained by the first pass, our second pass computes a high quality solution from a given viewpoint. Radiances and source radiances are estimated using Monte Carlo processes in the context of path tracing acceleration and also for final gather. Probability density functions (PDFs) are created at ray intersection points. For such a task, we initially used constant basis functions for the directional domain. After realizing of their limitations we proposed the Link Probabilities (LPs), which are objects with adaptive PDFs in the links-space.In order to take advantage of the effort invested for the construction of the LPs, we have devised two closely related progressive sampling strategies. In the second pass, instead of sampling each pixel individually, only a subset of samples is progressively estimated across the image plane. Our algorithms are inspired by the work of Michael D. McCool on anisotropic diffusion using conductance maps.The final chapter presents the conclusions of the thesis. Also possible lines of further research are suggested. / El objetivo de esta tesis es el desarrollo de algoritmos para la simulación del transporte de la luz en los entornos genéricos para generar imágenes de la alta calidad. Con este fin, primero hemos analizado los métodos existentes capaces de visualizar medios participativos, más concretamente los que tienen en cuenta la dispersión múltiple en los medios. Después, hemos ideado un par de métodos de dos pasos para el cómputo de esas imágenes. Para el primer paso hemos propuesto algoritmos que hacen frente a las escenas que deseamos tratar. El segundo paso utiliza la solución aproximada del primer paso para obtener la imagen final. La estructura de la disertación se presenta brevemente en lo que sigue.En el primer capítulo se discuten la motivación de la tesis y sus objetivos. También se resumen las contribuciones de la tesis y su organización. En el segundo capítulo se repasan los principios de la iluminación global para los ambientes genéricos, con las ecuaciones-más importantes (la ecuación de rendering y la ecuación de transporte) cuya solución constituye el problema global de iluminación. Para solucionar el problema global de iluminación, cierto número de métodos de múltiples pasos existen. Su objetivo es poder eliminar restricciones en el número de tipos de caminos de luz que se podrían tratar con una sola técnica, o aumentar su eficacia y/o exactitud. Hemos optado seguir esta filosofía, desarrollando un par de métodos de dos pasos para entornos genéricos.El tercer capítulo incluye el estudio de los métodos que utilizan la aproximación de dispersión simple, y también el estudio de los que consideran la dispersión múltiple.El cuarto capítulo está dedicado a nuestro método de primer paso, que computa un cálculo aproximado de la iluminación global. Conociendo las ventajas de los métodos jerárquicos, dos algoritmos concretos basados en jerarquías se han ampliado para ser más genéricos: radiosidad jerárquica con clustering y radiosidad jerárquica usando Monte Carlo. Nuestro segundo paso se considera en el capítulo siguiente. Usando la solución aproximada obtenida por el primer paso, el segundo paso computa una solución de la alta calidad para un punto de vista dado. Se estiman las radiancias usando procesos de Monte Carlo en el contexto de la aceleración de trazadores de rayos y también para final gather. Las funciones de densidad de probabilidad (PDFs) se crean en los puntos de interacción de los rayos. Para tal tarea, utilizamos inicialmente funciones constantes como base para el dominio direccional. Después de comprender sus limitaciones, propusimos establecer probabilidades directamente sobre los enlaces (link probabilities, o LPs), usando objetos con PDFs adaptativos en el espacio de los enlaces.Para aprovechar el esfuerzo invertido en la construcción de los LPs, hemos ideado dos estrategias de muestreo progresivas. En el segundo paso, en vez de muestrear cada pixel individualmente, solamente se estima progresivamente un subconjunto de muestras a través del plano de imagen. Nuestros algoritmos han sido inspirados en el trabajo de Michael D. McCool en la difusión anisotrópica usando mapas de conductancia.El capítulo final presenta las conclusiones de la tesis, y también sugiere las líneas posibles de investigación futura.

A modality device can today capture high resolution volumetric data sets and as the data resolutions increase so does the challenges of processing volumetric data through a visualization pipeline. Standard volume rendering pipelines often use a graphic processing unit (GPU) to accelerate rendering performance by taking beneficial use of the parallel architecture on such devices. Unfortunately, graphics cards have limited amounts of video memory (VRAM), causing a bottleneck in a standard pipeline. Multi-resolution techniques can be used to efficiently modify the rendering pipeline, allowing a sub-domain within the volume to be represented at different resolutions. The active resolution distribution is temporarily stored on the VRAM for rendering and the inactive parts are stored on secondary memory layers such as the system RAM or on disk. The active resolution set can be optimized to produce high quality renders while minimizing the amount of storage required. This is done by using a dynamic compression scheme which optimize the visual quality by evaluating user-input data. The optimized resolution of each sub-domain is then, on demand, streamed to the VRAM from secondary memory layers. Rendering a multi-resolution data set requires some extra care between boundaries of sub-domains. To avoid artifacts, an intrablock interpolation (II) sampling scheme capable of creating smooth transitions between sub-domains at arbitrary resolutions can be used. The result is a highly optimized rendering pipeline complemented with a preprocessing pipeline together capable of rendering large volumetric data sets in real-time.

The technique of volume rendering can be a powerful tool when visualizing 3D medical data sets. Its characteristic of capturing 3D internal structures within a 2D rendered image makes it attractive in the analysis. However, the applications that implement this technique fail to reach out to most of the supposed end-users at the clinics and radiology departments of today. This is primarily due to problems centered on the design of the Transfer Function (TF), the tool that makes tissues visually appear in the rendered image. The interaction with the TF is too complex for a supposed end-user and its capability of separating tissues is often insufficient. This thesis presents methods for detecting the regions in the image volume where tissues are contained. The tissues that are of interest can furthermore be identified among these regions. This processing and classification is possible thanks to the use of a priori knowledge, i.e. what is known about the data set and its domain in advance. The identified regions can finally be visualized using tissue adapted TFs that can create cleaner renderings of tissues where a normal TF would fail to separate them. In addition an intuitive user control is presented that allows the user to easily interact with the detection and the visualization.

På IKEA går produktionsflödet för en produktbild i dagsläget från konstruktionsritning till fotografering via tillverkning och montering. En produkt som är färdig för tillverkning definieras av sin mekaniska konstruktion och sina ytegenskaper. Ledtiden och kostnaden för bildproduktionen skulle kunna minskas betydligt om produkten kunde avbildas redan i detta stadium, utan att finnas tillverkad. För detta ändamål såg IKEA en möjlighet i att introducera ett nytt produktionsflöde där avancerad datorgrafik, grafisk teknik och bildbehandling omvandlar konstruktionsritningen till produktbild. Ambitionen är att från ritningen ta ut en 3D-modell, placera den i en omgivning, ljussätta och belägga den med material och av detta skapa en tryckbar produktbild som uppfyller företagets höga kvalitetskrav. Syftet med examensarbetet var att ta fram förslag på ett konkret sådant flöde genom att undersöka olika programvaror som skulle kunna användas samt att identifiera problemområden och komma med lösningsförslag på dessa. Flödet delades upp i de fem problemområdena konvertering, modellering, ljussättning, material och rendering som bearbetades parallellt. Fokus har under hela projektet legat på färghantering och upplevd bildkvalitet genom att korrekt färg- och detaljåtergivning i bilderna varit pekpinne och ledsagare. Konstruktionsritningarna som görs i SolidWorks har konverterats till 3D-modeller med programvaran PolyTrans. I 3ds max har produktmodellerna satts in i en miljö som liknar den verkliga fotostudion, belysts och belagts med material. Efter en studie av olika programvaror för rendering beslutades det att mental ray skulle användas varpå alla bilder skapats med denna. mental ray är en komplex renderare som beräknar ljussättning fysikaliskt riktigt vilket bidrar till fotorealistiska bilder. Examensarbetet handlade till mångt och mycket om att köra olika produkter genom flödet och testa med olika inställningar i de olika stegen. Flödet utvärderades kontinuerligt genom att bilderna som kom ut bedömdes visuellt. Dessutom genomfördes några tester för att undersöka inblandade programvarors eventuella brister vad gäller färghantering och upplevd bildkvalitet. Det slutliga resultatet av examensarbetet blev ett flöde som i stor utsträckning liknar arbetsflödet vid nuvarande bildproduktion. Med minimal insats från retuschavdelningen uppfyller bilderna de krav som ställs för att de skall kunna tryckas i IKEA katalogen.

In recent years, the utilization of 3D display systems became popular in many application areas. One of the most important issues in the utilization of these systems is to render the correct view to the observer based on his/her position. In this thesis, we propose and implement a single user view rendering system for autostereoscopic/stereoscopic displays. The system can easily be installed on a standard PC together with an autostereoscopic display or stereoscopic glasses (shutter, polarized, pulfrich, and anaglyph) with appropriate video card. Proposed system composes of three main blocks: view point detection, view point tracking and intermediate view reconstruction. Haar object detection method, which is based on boosted cascade of simple feature classifiers, is utilized as the view point detection method. After detection, feature points are found on the detected region and accordingly they are fed to the feature tracker. View point of the observer is calculated by using the tracked position of the observer on the image. Correct stereoscopic view is, then, rendered on the display. A 3D warping-based method is utilized in the system as the intermediate view reconstruction method. System is implemented on a computer with Pentium IV 3.0 GHz processor using E-D 3D shutter glasses and Creative NX Webcam.