Direct volume rendering is an algorithm used for displaying three-dimensional scalar data, like image from Computed Tomography. This algorithm makes use of a concept of Transfer functions for assigning optical properties to the data values. We studied two dimensional transfer functions, that besides primary values have additional dataset as an input. In particular, we studied computation of this secondary dataset with respect to the primary image function shape. This was done by analysing eigenvalues of the Hessian matrix in each image point. We proposed one formula and implemented several others for computing the probability that image point belongs to the blood vessel. Powered by TCPDF (www.tcpdf.org)

The purpose of this thesis was to find and implement an adaptive method, based on given data and hardware, for selecting different level-of-detail whilst preserving visual quality to the best extent possible. Another important aspect of the new method was that it had to be performance effective, since the target platform was an interactive direct volume rendering application. The project was targeted towards memory restricted systems in which it has previously been impossible to render large-scale volumetric datasets. The previous state of the target platform supports two detail levels: full and half, and does not implement any kind of prioritisation when selecting the level-of-detail of bricks. Apart from failing to render parts of the datasets, the old implementation is also lacking in that the top of the dataset always has the lowest prioritisation, which can prove problematic for certain datasets. An adaptive method which determines a suitable number of detail levels at run-time has been implemented. The new implementation has also reworked the way bricks are prioritised during rendering. The proposed algorithm prioritises bricks holding surface information as well as bricks that match the transfer-function configuration well. The results show that the proposed method is able to render large-scale datasets in limited environments whilst maintaining interactive frame-rates. The new brick selection algorithm is a step in the right direction towards solving the issue with parts of the dataset not being prioritised.

L'objectif de cette thèse est lerendu de scène virtuelles extrêmement détaillées.Nous nous intéressons plus particulièrementaux algorithmes de rendu de haute qualitéreposant sur du path tracing qui sont très largement utilisésdans l'industrie des effets spéciaux et pour calculerle rendu des films d'animations.Les grandes quantités de détail nécessaires à la modélisationde mondes virtuels crédibles soulèvent de sérieux problèmes d'efficacitédu rendu qui paralysent les studios et compliquent grandementle travail des artistes. Nous introduisons de nouveaux algorithmespour préfiltrer les objets 3D complexes à des échelles arbitraires,afin de réduire les temps de chargement, les coûts d'intersection des rayons lumineux,le calcul des matériaux et la quantité de bruit dans les images,le tout sans porter atteinte à la qualité du rendu.Nos contributions principales sont une nouvelle approchehybride de niveaux de détail qui allie les avantages des maillageset des représentations volumiques pour le préfiltrage des objets complexes àdes échelles arbitraires, ainsi qu'une nouvelle approchede préfiltrage pour le cas des volumes hétérogènes de haute résolution. / We address the problem of rendering extremely complex virtualscenes with large amounts of detail. We focuson high-end off-line rendering algorithms based on path tracing thatare intensively used in the special effects and 3D animation industries.The large amounts of detail required for creating believable virtual worldsraise important efficiency problemsthat paralyze production rendering pipelines andgreatly complicate the work of 3D artists.We introduce new algorithms for prefilteringcomplex 3D assets while preserving their appearanceat all scales, in order to reduce loading times,ray intersection costs, shading costs and Monte Carlo noise,without lowering the quality of rendered frames.Our main contributions are a new hybrid LODapproach that combines the benefits ofmeshes and volumetric representationsfor prefiltering complex 3D assets,as well as a new approach for prefilteringhigh-resolution heterogeneous participatingmedia.

In this thesis, the goal was to implement a method to do partial segmentation for general 3D volumetric datasets such as mummies, clay figurines or animal bodies. There are different approaches for segmenting volumes, such as automatic methods, semi-automatic methods and interactive methods. However, no automatic algorithm was found that could successfully segment any general 3D volume with high precision. Instead, the chosen approach are segmentation tools which allows the user to quickly and intuitively do partial segmentation from a 3D volume. The tools consist of a interactive 3D brush, a transfer function editor and a semi-automatic flood fill tool which performs region growing in 3D. User studies were carried out in order to evaluate the speed and effectiveness of the segmenting tools compared to the conventional method of segmenting using a stack of 2D images. Based on the user studies the results shows that the proposed method is faster compared to the old method as long as high precision is not required.

Visualization is the process of making something perceptible to the mind or imagination. The techniques for producing visual imagery of volumetric data have advanced immensely during the last decades to a point where each produced image can include an overwhelming amount of information. An increasingly viable solution to the limitations of the human sense of visual perception is to make use of not only vision, but also additional senses. This thesis presents recent work on the development of principles and algorithms for generating representations of volumetric data through the sense of touch for the purpose of visualization. The primary idea introduced in this work is the concept of yielding constraints, that can be used to provide a continuous set of shapes as a representation of features of interest in various types of volumetric data. Some of the earlier identified standard human exploratory procedures can then be used which enables natural, intuitive and effective interaction with the data. The yielding constraints concept is introduced, and an algorithm based on haptic primitives is described, which forms a powerful yet versatile implementation of the yielding constraints. These methods are also extended to handle time-varying, moving and low quality data. A framework for multimodal visualization has been built on the presented methods, and this is used to demonstrate the applicability and versatility of the work through several example applications taken from different areas.

abstract: The Dual Marching Tetrahedra algorithm is a generalization of the Dual Marching Cubes algorithm, used to build a boundary surface around points which have been assigned a particular scalar density value, such as the data produced by and Magnetic Resonance Imaging or Computed Tomography scanner. This boundary acts as a skin between points which are determined to be "inside" and "outside" of an object. However, the DMT is vague in regards to exactly where each vertex of the boundary should be placed, which will not necessarily produce smooth results. Mesh smoothing algorithms which ignore the DMT data structures may distort the output mesh so that it could incorrectly include or exclude density points. Thus, an algorithm is presented here which is designed to smooth the output mesh, while obeying the underlying data structures of the DMT algorithm. / Dissertation/Thesis / M.S. Computer Science 2011

This master thesis is focused on volumetric data rendering and on highlighting and visualization of the selected cells of the model organisms. These data are captured by a confocal deconvolution microscope. Input data form one large volumetric block containing separate slices. This data block is rendered by an applicable method and then are identified and visualized the cells marked by the GFP (Green Fluorescent Protein) process or by chlorophyle fluorescency. The principal aim of this work is to find out the preferably optimal effective method enabling this highlighting, most preferably working without a manual check. Due to the data structure, this ambition seems hardly realizable, so it suffices to find out a manual working method. The last step is to embed the results of this work into FluorCam application, the confocal deconvolution microscope data visualizer.

This thesis deals with a graph cut approach for segmentation of the anatomical structures in volumetric medical images. The method used requires some voxels to be a priori identified as object or background seeds. The goal of this thesis is implementation of the graph cut method and construction of an interactive tool for segmentation. Selected metod's behaviour is examined on two datasets with manually-guided segmentation results. Testing is in one case focused on the influence of method parameters on segmentation results, while in the other deals with method tolerance towards various signal-to-noise and contrast-to-noise ratios on input. To assess the consistency of a given segmentation with the ground-truth the F-measure is used.

This work discourses about methods of rendering volumetric data such as clouds or smoke in computer graphics and implementation of this feature to existing application. The first part is summary of techniques and tricks used in computer graphics to display such objects in scene, their pros and cons and the most used techniques of displaying volumetric data. Next part is more closely focused to choosed technique of rendering volumetric data with consideration of light behavior inside the volume (also called participating media) and basic relationships used used in computation. In following part of work there is short list of applications - renderers used to realistic rendering of scene, which are suitable for implementation of selected volumetric data rendering algorithm. Selected application - Blender is describled more deeply including its inner structure, especially rendering engine. Last part of work is dedicated to design, implementation and integration of rendering algorithm itself.

Made available in DSpace on 2016-08-17T14:52:58Z (GMT). No. of bitstreams: 1 Fernando Jorge Cutrim Demetrio.pdf: 680959 bytes, checksum: 8bfd83d8940d01500dfe55ffeccc7148 (MD5) Previous issue date: 2005-04-01 / This work describes the development of an algorithm for visualization of compressed volumetric data with a local cosine transform scheme, that minimizes the blocking artefacts generated by transform compression methods, and makes possible the visualization of large volume data in computer with limited memory resources. We also present the results obtained for the visualization process . / Este trabalho descreve o desenvolvimento de um algoritmo para visualização de dados volumétricos comprimidos baseado na transformada do cosseno local, que minimiza os artefatos nos blocos gerados pelo método de compressão, e possibilita a visualização de grandes volumes em computadores com recursos limitados de memória. Nós apresentamos também os resultados obtidos pelo processo de visualização.