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Reconstructing a 3-dimensional scene from a set of2-dimensional images is a fundamental problem in computervision. A system capable of performing this task can be used inmany applications in robotics, architecture, archaeology,biometrics, human computer interaction and the movie andentertainment industry. Most existing reconstruction approaches exploit one sourceof information to tackle the problem. This is the motion of thecamera, the 2D images are taken from different viewpoints. Weexploit an additional information source, the reference plane,which makes it possible to reconstruct difficult scenes whereother methods fail. A real scene plane may serve as thereference plane. Furthermore, there are many alternativetechniques to obtain virtual reference planes. For instance,orthogonal directions in the scene provide a virtual referenceplane, the plane at infinity, or images taken with a parallelprojection camera. A collection of known and novel referenceplane scenarios is presented in this thesis. The main contribution of the thesis is a novel multi-viewreconstruction approach using a reference plane. The techniqueis applicable to three different feature types, points, linesand planes. The novelty of our approach is that all cameras andall features (off the reference plane) are reconstructedsimultaneously from a single linear system of imagemeasurements. It is based on the novel observation that camerasand features have a linear relationship if a reference plane isknown. In the absence of a reference plane, this relationshipis non-linear. Thus many previousmethods must reconstructfeatures and cameras sequentially. Another class of methods,popular in the literature, is factorization, but, in contrastto our approach, this has the serious practical drawback thatall features are required to be visible in all views. Extensiveexperiments show that our approach is superior to allpreviously suggested reference plane and non-reference planemethods for difficult reference plane scenarios. Furthermore, the thesis studies scenes which do not have aunique reconstruction, so-called critical configurations. It isproven that in the presence of a reference plane the set ofcritical configurations is small. Finally, the thesis introduces a complete, automaticmulti-view reconstruction system based on the reference planeapproach. The input data is a set of images and the output a 3Dpoint reconstruction together with the correspondingcameras.

Modern medical imaging techniques provide an increasing amount of high-dimensional and high-resolution image data that need to be visualized, analyzed, and interpreted for diagnostic and treatment planning purposes. As a consequence, efficient ways of exploring these images are needed. In order to work with specific patient cases, it is necessary to be able to work directly with the medical image volumes and to generate the relevant 3D structures directly as they are needed for visualization and analysis. This requires efficient tools for segmentation, i.e., separation of objects from each other and from the background. Segmentation is hard to automate due to, e.g., high shape variability of organs and limited contrast between tissues. Manual segmentation, on the other hand, is tedious and error-prone. An approach combining the merits from automatic and manual methods is semi-automatic segmentation, where the user interactively provides input to the methods. For complex medical image volumes, the interactive part can be highly 3D oriented and is therefore dependent on the user interface. This thesis presents methods for interactive segmentation and visualization where true 3D interaction with haptic feedback and stereo graphics is used. Well-known segmentation methods such as fast marching, fuzzy connectedness, live-wire, and deformable models, have been tailored and extended for implementation in a 3D environment where volume visualization and haptics are used to guide the user. The visualization is accelerated with graphics hardware and therefore allows for volume rendering in stereo at interactive rates. The haptic feedback is rendered with constraint-based direct volume haptics in order to convey information about the data that is hard to visualize and thereby facilitate the interaction. The methods have been applied to real medical images, e.g., 3D liver CT data and 4D breast MR data with good results. To provide a tool for future work in this area, a software toolkit containing the implementations of the developed methods has been made publicly available.

This thesis proposes a novel image primitive - the <b>diffusion curve</b>. This primitive relies on the principle that images can be defined via their discontinuities, and concentrates image features along contours. The diffusion curve can be defined in vector graphics, as well as in raster graphics, to increase user control during the process of art creation. The <i>vectorial diffusion curve</i> primitive augments the expressive powers of vector images by capturing complex spatial appearance behaviors. Diffusion curves represent a simple and easy-to-manipulate support for complex content representation and edition. In <i>raster</i> images, diffusion curves define a higher level structural organization of the pixel image. This structure is used to create simplified or exaggerated representations of photographs in a way consistent with the original image content. Finally, a fully automatic vectorization method is presented, that converts raster diffusion curve to vector diffusion curve.

No description available.

Medical imaging plays an increasingly important role in modern healthcare. In medical imaging, it is often relevant to relate different images to each other, something which can prove challenging, since there rarely exists a pre-defined mapping between the pixels in different images. Hence, there is a need to find such a mapping/transformation, a procedure known as image registration. Over the years, image registration has been proved useful in a number of clinical situations. Despite this, current use of image registration in clinical practice is rather limited, typically only used for image fusion. The limited use is, to a large extent, caused by excessive computation times, lack of established validation methods/metrics and a general skepticism toward the trustworthiness of the estimated transformations in deformable image registration. This thesis aims to overcome some of the issues limiting the use of image registration, by proposing a set of technical contributions and two clinical applications targeted at improved clinical efficiency. The contributions are made in the context of a generic framework for non-parametric image registration and using an image registration method known as the Morphon.  In image registration, regularization of the estimated transformation forms an integral part in controlling the registration process, and in this thesis, two regularizers are proposed and their applicability demonstrated. Although the regularizers are similar in that they rely on local structure analysis, they differ in regard to implementation, where one is implemented as applying a set of filter kernels, and where the other is implemented as solving a global optimization problem. Furthermore, it is proposed to use a set of quadrature filters with parallel scales when estimating the phase-difference, driving the registration. A proposal that brings both accuracy and robustness to the registration process, as shown on a set of challenging image sequences. Computational complexity, in general, is addressed by porting the employed Morphon algorithm to the GPU, by which a performance improvement of 38-44x is achieved, when compared to a single-threaded CPU implementation. The suggested clinical applications are based upon the concept paint on priors, which was formulated in conjunction with the initial presentation of the Morphon, and which denotes the notion of assigning a model a set of properties (local operators), guiding the registration process. In this thesis, this is taken one step further, in which properties of a model are assigned to the patient data after completed registration. Based upon this, an application using the concept of anatomical transfer functions is presented, in which different organs can be visualized with separate transfer functions. This has been implemented for both 2D slice visualization and 3D volume rendering. A second application is proposed, in which landmarks, relevant for determining various measures describing the anatomy, are transferred to the patient data. In particular, this is applied to idiopathic scoliosis and used to obtain various measures relevant for assessing spinal deformity. In addition, a data analysis scheme is proposed, useful for quantifying the linear dependence between the different measures used to describe spinal deformities.

Global illumination is an important factor when striving for photo realism in computergraphics. This thesis describes why this is the case, and why global illumination is considered acomplex problem to solve. The problem becomes even more demanding when considering realtime purposes. Resent research has proven it possible to produce global illumination in realtime. Therefore the subject of this thesis is to compare and evaluate a number of those methods. An implementation is presented based on the Imperfect shadow maps method, which per se isbased on instant radiosity and reflective shadow maps. The implementation is able to renderplausible global illumination effects in real time, for fully dynamic scenes. With conclusions that while it demonstrably is possible to provide believable global illum-ination in real time, it is not without shortcomings. In every case approximations or restrictionshas to be done to some extent, sometimes leading to wrong results. Though in most cases, notvisually unpleasing by a great deal. The final conclusion is that global illumination is possible on current hardware, with believablequality and good speed. Showing great potential for future implementations on next generationof hardware.

Det här arbetet har gått ut på att jämföra två algoritmer för bildbaserad rendering. Båda algoritmerna använder två bilder som spelats in med formatet MultiView plus depth för att rendera nya mellanliggande vyer av en tredimensionell scen. De tvådimensionella bilderna är kompletterade med djupvärden för varje bildpunkt. Renderingen kan då utföras genom perspektivriktiga transformationer där alla bildpunkters nya positioner projiceras individuellt. I samband med renderingen behöver bland annat mätfel i de ursprungliga bilderna samt skymda partier hanteras. Algoritm I gör det delvis genom utjämning av skarvararna mellan bildernas bidrag till den nya vyn. Algoritm II bygger på att bilderna delas upp i lager där de lager som ansetts vara säkra prioriteras framför lager som har bedömts vara mer riskabla. Algoritmerna har implementerats i Matlab och algoritm II har modifierats genom kompletteringar av dess regler för prioriteringen av lagren till mer komplicerade scener. Algoritm II har visat sig vara bättre på att bevara detaljer i de renderade vyerna och håller en jämnare hastighet vid renderingarna. Den ger även högre och jämnare resultat vid jämförelse med kvalitetsmåttet PSNR men vid jämförelser med MSSIM har den däremot fått något lägre värden. De ytterligare stegen vid renderingen har även ökat renderingstiderna med upp till 40 % jämfört med algoritm I. Författaren ger förslag på områden för fortsatt utveckling av algoritm II. Till exempel bör algoritmen testas vidare för att avgöra om de använda gränsvärdena är generella eller om de måste anpassas till olika scener. / This thesis has been aimed at comparing two algorithms for image-based renderings. Both algorithms uses two images recorded with the MultiView plus depth format, to render new intermediate views of a three-dimensional scene. The two-dimensional images extensions with depth values for each pixel, makes it possible to perform the image warping as perspective projections of all individually pixels to their new positions. During rendering, such as measurement error in the original images and occlusions has to be handled. Algorithm I is partly based on smoothening the joints between the contributions from the two images to the novel view. Algorithm II divides the images into layers, in which layers consid-ered safe has priority over layers that have been defined as more risky. The algorithms have been implemented in Matlab and algorithm II has been modified through additions to the priority rules for the layers to more complex scenes. Algorithm II has proven to be better at preserving the details in the rendered views, and maintains a less varying speed when rendering. It also provides higher and more consistent PSNR values, but in comparison using MSSIM the values are slightly lower. The additional steps have also increased the rendering times by up to 40 % compared to algorithm I. The author suggests areas for further development of algorithm II. For example, the algorithm should be tested further to determine if the used thresholds are general or whether they must be adapted to different scenes.

Creating realistic virtual hair consists of several major areas: creating the geometry, moving the hair strands realistically and rendering the hair. In this thesis, a background survey covering each one of these areas is given. A node-based, procedural hair system is presented, which utilizes the capabilities of modern GPUs. The hair system is implemented as a plugin for Autodesk Maya, and a user interface is developed to allow the user to control the various parameters. A number of nodes are developed to create effects such as clumping, noise and frizz. The proposed system can easily handle a variety of hairstyles, and pre-renders the result in real-time using a local shading model.

A modular and area-efficient 3D graphics accelerator for tile based rendering in FPGA systems has been designed and implemented. The accelerator supports a subset of OpenGL, with features such as mipmapping, multitexturing and blending. The accelerator consists of a software component for projection and clipping of triangles, as well as a hardware component for rasterization, coloring and video output. Trade-offs made between area, performance and functionality have been described and justified. In order to evaluate the functionality and performance of the accelerator, it has been tested with two different applications. / En modulär och utrymmeseffektiv 3D-grafikaccelerator för tile-baserad rendering i FPGA-system har designats och implementerats. Acceleratorn stöder en delmängd av OpenGL med funktioner som mipmapping, multitexturering och blending. Acceleratorn är uppdelad i en mjukvarudel för projektion och klippning av trianglar och en hårdvarudel för rastrering, färgsättning och utritning till skärm. Avvägningar som gjorts mellan area, prestanda och funktionalitet har beskrivits och motiverats. För att evaulera funktionalitet och prestanda har acceleratorn testats med två olika applikationer.