The EU funded HAPTEX project aimed to create a virtual reality system that allowed a user to explore and manipulate a suspended virtual textile with the thumb and index finger. This was achieved through a combination of a tactile renderer on the fingertips for surface textures and a force feedback system for deformation of the virtual material. This project focuses on the tactile rendering component of this system, which uses a tactile display developed at the University of Exeter. The 24 pin display is driven by piezoelectric bimorphs. Each of the pins can be driven independently, allowing for a variety of different sensations to be transmitted to the fingertip. The display is driven by rendering software that uses a spatial spectrum of the intended surface, in combination with the frequency response of touch receptors in the skin, position on the surface, and exploration velocity to produce a signal that is intended to recreate the sensation of exploring the surface texture. The output signal on each of the 24 contactors is a combination of high (320 Hz) and low (40 Hz) frequency sine waves. In this project, the tactile renderer is initially evaluated based on its ability to recreate the sensations of exploring particular textured surfaces. The users were asked to rank virtual textures in order of similarity to a real target texture. The results of the initial test were disappointingly low, with a 38.1±3.1% correct identification rate. However, feedback from this initial test was used to make improvements to the rendering strategy. These improvements did not give a significant improvement in identification (41.3±1.6%). Finally, the tests were repeated with a target virtual texture instead of the real one used in previous tests. This test yielded a higher identification rate (64.1±5.5%). This increase in identification suggests that the virtual textures are distinguishable but that they not always accurate recreations of the real textures they are mimicking.

No description available.

Ingeniero Civil en Computación / El trabajo desarrollado durante este tema de memoria se enmarcó en el ámbito de experimentación física sobre sistemas de partículas. El objetivo fue diseñar y desarrollar una herramienta de visualización de sistemas de partículas en 3D, que permita manejar grandes volúmenes de datos, visualizarlos rápidamente y proveer controles de visualización. El Departamento de Física de esta Facultad realiza diversos experimentos y simulaciones computacionales de materiales granulares compuestos por miles o millones de partículas esféricas. Una buena herramienta de visualización de estas simulaciones permite a los investigadores realizar un análisis más riguroso y concluir correctamente sobre los experimentos. Las herramientas con que se contaba, previo a este trabajo, poseían falencias importantes que no permitían obtener el máximo provecho de las simulaciones. El trabajo realizado se dividió en cuatro etapas. La primera etapa consistió en recoger los requerimientos que debía satisfacer la aplicación para cumplir con los objetivos planteados. En base a los requerimientos tomados se comenzó la segunda etapa, diseñar la arquitectura del sistema. La arquitectura debió considerar un software creado previamente para monitorear las simulaciones, el cual establece la conexión con éstas y obtiene su información y datos relevantes. Un hito desafiante en esta etapa fue adaptar la herramienta disponible a los requerimientos pedidos. Como resultado de esta segunda etapa se obtuvo un diseño de la estructura del software utilizando el paradigma de programación orientada a objetos y utilizando diversos patrones de diseño a fin de mejorar la calidad del software. La tercera etapa consistió en implementar la aplicación. Para ello, se creó una interfaz de usuario adecuada a los requisitos y con herramientas de control que faciliten el uso de la aplicación. Luego se implementaron las funcionalidades disponibles en la interfaz, dentro de las cuales se encuentran: Rotar libremente la escena, distinguir partículas en base a su tipo y velocidad, graficar partículas de distinto radio, conectarse a distintas simulaciones, generar grabaciones de video y capturar imágenes de la visualización, entre otras. La última etapa consistió en testing y optimización. Se hicieron pruebas para medir la calidad de la aplicación, optimizando el software de acuerdo a los resultados obtenidos. Como resultado se obtuvo una aplicación robusta, extensible y fácil de usar, la cual permite visualizar simulaciones físicas de sistemas de alrededor de 500.000 partículas de manera eficiente y facilita el análisis de éstas.

Title: Efficient visibility calculation for light transport simulation in participating media Author: Čestmír Houška Department / Institute: Department of Software and Computer Science Educa- tion Supervisor of the master thesis: doc. Ing. Jaroslav Křivánek, Ph.D. Abstract: This thesis investigates the use of acceleration methods for the testing of visibility in light transport calculation algorithms with the emphasis on conser- vativeness and low accelerated query overhead. Several published non-directional and directional distance field methods are presented with the description of their characteristic properties. Two of these methods are then implemented and thor- oughly tested in an existing rendering framework on a path tracing volumetric integrator as well as on an own implementation of a ray marching single scattering integrator. A method that further accelerates the original distance field methods by pre-caching results of some of the queries is also proposed, implemented and tested. Furthermore, several possible extensions to this method are outlined. Keywords: computer graphics, rendering, participating media, visibility

När en användare idag efterfrågar rendering av en kartvy i en applikation behöver en server först rendera en bild utifrån given geografisk data och därefter skicka bilden till klientens mobila enhet. Detta kan resultera i höga responstider, speciellt för användare som befinner sig i områden med bristfällig täckning. I denna studie utvärderas en alternativ lösning där rendering istället sker direkt på klientens enhet. En prototyp av en mobil kartapplikation med stöd för lokal rendering av geografisk rådata utvecklas och utvärderas utefter en konstant för acceptabel fördröjning vid visualisering av information. Resultatet av testerna visar att prototypens prestanda är beroende av mängden information som ska visas. För högre zoomnivåer ger prototypen ett tillfredsställande resultat, men vidare åtgärder krävs för de lägre nivåerna. De främsta utmaningarna vid utvecklingen av applikationen redovisas och förbättringsförslag för fortsatt utveckling framförs.

Real-time performance is necessary for video-rate processing. By utilizing GPU for acceleration, we propose an efficient technique for the warped display of surveillance video signal. Usually, there are regions of interest (ROIs) in video surveillance, such as entrance or exit, and moving objects or persons. The ii surveillant wants to see more of the ROIs, but also wants to have an overview of the whole surveillance scope. The warped display solves this conflict by locally zooming in the ROIs. / The above warped-display technique may not be able to capture more information. It only provides an efficient way to display the captured frame. To solve this problem, we propose a novel technique to automatically adjust the exposure and capture more information. Traditional automatic exposure control (AEC) is usually based on the intensity level. On the other hand, our technique is based on the information theory and the amount of information is measured by Shannon entropy. The computation of entropy is accelerated by GPU to achieve the video-rate performance. / Volume rendering is another hot research area. In this area, isosurfaces have been widely adopted to reveal the complex structures in volumetric data, due to its fine visual quality. We describe a GPU-based marching cubes (MC) algorithm to visualize multiple translucent isosurfaces. With the proposed parallel algorithm, we can naturally generate triangles in order, which facilitates the visibility-correct visualization of multiple translucent isosurfaces without computationally expensive sorting. Upon a commodity GPU, our implementation can extract isosurfaces from a high-resolution volume in real time and render the result. / We first present a GPU-friendly image rendering framework, which can achieve a wide range of non-photorealistic rendering (NPR) effects. Most of these effects usually require the tailor-made algorithms. By feeding with constant kernels, the usage of our framework is as simple as that of discrete linear filtering. However, our framework is non-linear and hence can mimic complex NPR effects, such as watercolor, painting, sketching, and so on. The core of our framework is the cellular neural networks (CNN). By relaxing the constraints in the traditional CNN, we demonstrate that various interesting and convincing results can be obtained. As CNN is locally connected and designed for massively parallel hardware, it fits nicely into the GPU hardware and the performance is improved a lot. / With the development of graphics processing unit (GPU), it is more and more efficient to solve complex algorithms with GPU because of its highly parallel structure and fast floating point operations. These complex algorithms were usually implemented with CPU previously. In this thesis, we propose several GPU-friendly concepts and algorithms to address some problems of visual computing, including: image rendering, video rendering, and volume rendering. / Wang Guangyu. / "September 2007." / Advisers: Pheng Am Heng; Tien-Tsin Wong. / Source: Dissertation Abstracts International, Volume: 69-08, Section: B, page: 4865. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references (p. 115-131). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.

Global illumination adds tremendous visual richness to rendered images. Unfortunately, such illumination proves quite costly to compute, and is therefore often coarsely approximated by interactive applications, or simply omitted altogether. Global illumination is often quite low-frequency, aside from sharp changes at discontinuities. This thesis describes three novel multiresolution image-space methods that exploit this characteristic to accelerate rendering speeds. These techniques run completely on the GPU at interactive rates and require no precomputation, allowing fully dynamic lighting, geometry, and camera. The first approach, multiresolution splatting, is a novel multiresolution method for rendering indirect illumination. This work extends reflective shadow maps, an image space method that splats contributions from secondary light sources into eye-space. Splats are refined into multiresolution patches, rendering indirect contributions at low resolution where lighting changes slowly and at high resolution near discontinuities; this greatly reduces GPU fill rate and enhances performance. The second method, image space radiosity, significantly improves the performance of multiresolution splatting, introducing an efficient stencil-based parallel refinement technique. This method also adapts ideas from object-space hierarchical radiosity methods to image space, introducing two adaptive sampling methods that allow much finer sampling of the reflective shadow map where needed. These modifications significantly improve temporal coherence while maintaining performance. The third approach adapts these techniques to accelerate the rendering of direct illumination from large area light sources. Visibility is computed using a coarse screen-space voxelization technique, allowing binary visibility queries using ray marching. This work also proposes a new incremental refinement method that considers both illumination and visibility variations. Both diffuse and non-diffuse surfaces are supported, and illumination can vary over the surface of the light, enabling dynamic content such as video screens.

The main purpose of this research project was to implement a combination of computer graphics and processing to generate displays that will aid in the visualization of the colour rendering properties of a range of light sources, including the new generation of high-output LEDs (light emitting diodes) that are becoming widely adopted in general lighting service. The CIE (International Commission on Illumination) has developed a colour appearance model CIECAM02 for use in colour imaging and colour management, and this model is utilized in this work. This thesis describes the design and construction of a computer-based model that can be used as a research tool for the simulation and demonstration of the colour rendering properties of various artificial light sources. It is a comprehensive study of the colour models and measurement procedures currently in use in the lighting industry, as recommended by the CIE. This research project focused on the display of a set of surface colour patches as if they were illuminated by a specific light source, and the simultaneous display of two such sets to demonstrate the surface colour differences arising from the use of the two different light sources. A VIS (virtual imaging system) has been developed to display the colour properties of a series of test colour samples under different light sources. This thesis describes the computer models developed for the representation and display of surface colours in general, and colour rendering in particular. The designed system computes and displays the colour of each sample from a knowledge of the light-source spectrum and the spectral reflectance of each surface. It can simultaneously display the colours resulting from illumination by two different sources. In addition, the system computes the colour appearance differences for two sets of colours using the CIECAM02 colour appearance model. Subjective and objective tests were taken to validate the computed results. The VIS has been designed and implemented. It also has been tested by 21 observers and we believe that it will be a powerful research tool for the lighting industry, especially in relation to colour rendering.

In computer graphics a projection describes the mapping of scene geometry to the screen. While linear projections such as perspective and orthographic projection are common, increasing applications are being found for nonlinear projections, which do not necessarily map straight lines in the scene to straight lines on the screen. Nonlinear projections occur in reflections and refractions on curved surfaces, in art, and in visualisation. This thesis presents a new nonlinear projection technique called a trilinear projection that is based on the trilinear interpolation of surface normals used in Phong shading. Trilinear projections can be combined to represent more complicated nonlinear projections. Nonlinear projections have previously been implemented with ray tracing, where rays are generated by the nonlinear projections and traced into the scene. However for performance reasons, most current graphics software uses scanline rendering, where a scene point is imaged on a screen as a function of the projection parameters. The techniques developed in this thesis are of this nature. This thesis presents several algorithms used in trilinear projection: 1. An algorithm to analytically determine which screen locations image a given scene point. 2. An algorithm that correctly connects projected vertices. Each scene point may be imaged multiple times, which means a projected scene triangle may form from one to four different shapes of from two to nine vertices. Once connected, the projected shapes may be rendered with standard scanline algorithms. 3. An algorithm to more accurately render the curved edges between projected vertices. 4. A scene-space edge-clipping algorithm that handles continuity issues for projected shapes across composite projections. The trilinear projection technique is demonstrated in two different application areas: visualisation, and reflections and refractions. Specifically, various nonlinear projections that are congruent with pre-existing visualisation techniques are implemented with trilinear projections and a method for approximating the reflections and refractions on curved surfaces with trilinear projections is presented. Finally, the performance characteristics of the trilinear projection is explored over various parameter ranges and compared with a naive ray tracing approach.

<p>Image rendering is the process of creating realistic computer images from  geometric models and physical laws of light and reflection. This master thesis deals mainly with the numerical intricacies of implementing an image renderer using spherical harmonics. It investigates how to calculate the reflection of light in a surface using the Phong model, and employs ray tracing to create a realistic image of a geometric model. Further, it investigates different ways of calculating the spherical harmonic representation of a function defined on the sphere. The thesis also deals with the implementation of self-shadowing, and the effects of adding this component to the rendering equation.</p>