published_or_final_version / abstract / Computer Science / Master / Master of Philosophy

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 167-179).

Made available in DSpace on 2014-06-11T19:22:25Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-03-30Bitstream added on 2014-06-13T18:08:14Z : No. of bitstreams: 1 demarqui_en_me_prud.pdf: 4998562 bytes, checksum: 5482d66ba7d8db635205618558aeb138 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Este trabalho propõe uma metodologia monoscópica para a determinação automática da altura de edifícios em fotografias aéreas digitais, baseando-se no deslocamento radial dos pontos projetados no plano imagem e na geometria formada no momento de obtenção da fotografia aérea. O conhecimento da altura de edifícios pode ser utilizado para a modelagem da superfície em áreas urbanas, estudos para a instalação de antenas de transmissão de sinais, planejamento de rotas para aeronaves, geração de true-orthophoto etc.. A metodologia emprega um conjunto de etapas para a detecção das bordas dispostas radialmente em relação ao sistema de coordenadas fotogramétrico, sendo que estas bordas representam as arestas laterais dos edifícios registradas na fotografia. Na primeira etapa realiza-se a redução do espaço de busca através da detecção das sombras projetadas pelos edifícios, gerando sub-imagens das áreas no entorno de cada sombra detectada. Na seqüência, é realizada a extração de bordas e conexão dos pixels destas sub-imagens. As bordas são analisadas individualmente para identificar qual par, dentre os pontos que compõem a borda, melhor corresponde aos extremos da aresta lateral do edifício. Os critérios utilizados para a seleção dos pares de pontos são os seguintes: análise do coeficiente linear da equação da reta formada pelo par de pontos; distância entre os pontos; e grau de sobreposição com a borda rotulada. Deste modo, a partir da seleção das arestas laterais, assim como o conhecimento da altura de vôo, são calculadas as alturas destes edifícios. Os resultados alcançados nos testes realizados com imagens reais se mostraram promissores para a identificação das arestas e cálculo da altura de edifícios. / This work proposes an automatic extraction of buildings height in digital images through a monoscopic methodology. Surface modeling of urban areas planning of aircraft routes, true-orthophoto and so on, can be performed by knowing the buildings heights. In photographs taken from an aircraft the buildings edges appear as radial lines due to the relief displacement, which occurs radially from the principal point. The first step of the methodology consists on the sub-images creation with the aim to reduce the search space on image. Thus, its used a shadows extraction procedure, by selecting only those with the biggest area (projected at ground) according to threshold. The edge extraction and pixels connection are performed for each sub-image produced and analyzed individually in order to identify if they belong to a building. The adopted criteria are based on the linear coefficient of straight line, the distance and the overlapping degree with regard to the labeled edge. With the lateral edges selected and the knowledge of the flight height, the buildings heights can be calculated. The experimental results obtained with real images show that the proposed approach is suitable to perform the automatic identification of the buildings height in digital images.

This thesis describes the implementation of a shadowing system able to produce hard shadows. Shadow mapping is the most common real-time shadowing algorithm but it suffers from severe aliasing artifacts and self-shadowing effects. Different advanced techniques based on Shadow Mapping are implemented in this thesis with the objective of creating accurate hard shadows. First, an implementation based on Cascaded Shadow Maps is presented. This technique improves the visual quality of shadow mapping by using multiple smaller shadow maps instead of a large one. The technique addresses the fact that objects near the viewer require a higher shadow map resolution than objects far away. The second technique presented is Sub-pixel Shadow Mapping. By storing information about occluding triangles in the shadow map this technique is able to produce accurate hard shadows with sub-pixel precision. Both methods can be combined in order to improve the resulting shadow quality. Finally, a collection of advanced biasing techniques that minimize the self-hadowing artifacts generated by shadow mapping are presented. The final implementation achieves real-time performances with considerably improved quality compared to standard shadow mapping.

Prior research shows that stylistic ad manipulations (i.e., the style or manner in which product visuals are presented in an ad) impact consumer perceptions (Yang, Zhang and Peracchio 2010). This dissertation explores the impact of presence (versus absence) of a product’s shadow in the ad frame, as a visual stylistic manipulation influencing consumer ad perceptions. While many stylistic manipulations have been explored in the past, product shadows in how they impact ad perceptions have not been explored. Drawing on a holistic understanding on object shadows from the visual art, cognition and psychophysics literature streams, this dissertation investigates how product shadows impact ad perceptions. It applies theoretical tenants of Gestalt psychology, Construal Level Theory (CLT), and information paradigms including Signal Detection Theory (SDT) in deriving seven specific hypotheses. It also tests for moderating factors (such as individual consumer aesthetics, gestalt versus component visual processing modes, and product luxury positioning) that may alter consumer ad evaluations and ad effectiveness perceptions based on this stylistic manipulation of product shadow. Findings from this dissertation reveal that the presence (vs. absence) of a product’s shadow in an ad frame enhances the product’s visual form. This visual appraisal of the product in the ad frame further improves the ad’s overall evaluations. The effects of a product shadow on ad attitudes is positively moderated by an individual’s aesthetic tendencies (specifically their response tendencies towards visual aesthetics), a gestalt-focused (vs. component-focused) visual processing mode, as well as a luxury based ad’s positioning. There is also some support for negative effects of product shadows in component-focused ad scenarios, where they act as visual impairments rather than enhancers of the product form and aesthetics. Theoretically, this dissertation extends prior research on stylistic manipulations of product images in visual ad frames, while building upon established ad communication paradigms, including AIDA and Hierarchical Processing Model, HPM (Peracchio and Meyers-Levy 2005; Yang, Zhang and Peracchio 2010). Managerially, findings from this dissertation have implications for print, online, in-store and thus, any form of visual advertising portraying a product form. It outlines specific contexts under which managers can systematically employ (or evade) product shadows to not only enhance ad evaluations, but also to optimize their ad message efficacies. Stylistic image manipulations comprise production elements (e.g., camera angles), and only affect the way in which the product is displayed, i.e., not the core product image itself (Peracchio and Meyers-Levy 2005; Yang, Zhang and Peracchio 2010). Hence, these can be employed as strategic tools towards ad effectiveness (Barry and Howard 1990). Marketers can not only specifically target and position promotions incorporating product shadows towards aesthetically-attuned consumers, but also save advertising costs by omitting them if their presence hinders the communication of the intended message in certain scenarios.

This dissertation explores algorithms for rendering optimization realizable within a modern, complex rendering engine. The first part contains optimized rendering algorithms for ray tracing. Ray tracing algorithms typically provide properties of simplicity and robustness that are highly desirable in computer graphics. We offer several novel contributions to the problem of interactive ray tracing of complex lighting environments. We focus on the problem of maintaining interactivity as both geometric and lighting complexity grows without effecting the simplicity or robustness of ray tracing. First, we present a new algorithm called occlusion caching for accelerating the calculation of direct lighting from many light sources. We cache light visibility information sparsely across a scene. When rendering direct lighting for all pixels in a frame, we combine cached lighting information to determine whether or not shadow rays are needed. Since light visibility and scene location are highly correlated, our approach precludes the need for most shadow rays. Second, we present improvements to the irradiance caching algorithm. Here we demonstrate a new elliptical cache point spacing heuristic that reduces the number of cache points required by taking into account the direction of irradiance gradients. We also accelerate irradiance caching by efficiently and intuitively coupling it with occlusion caching. In the second part of this dissertation, we present optimizations to rendering algorithms for participating media. Specifically, we explore the implementation and use of photon beams as an efficient, intuitive artistic primitive. We detail our implementation of the photon iii beams algorithm into PhotoRealistic RenderMan (PRMan). We show how our implementation maintains the benefits of the industry standard Reyes rendering pipeline, with proper motion blur and depth of field. We detail an automatic photon beam generation algorithm, utilizing PRMan shadow maps. We accelerate the rendering of camera-facing photon beams by utilizing Gaussian quadrature for path integrals in place of ray marching. Our optimized implementation allows for incredible versatility and intuitiveness in artistic control of volumetric lighting effects. Finally, we demonstrate the usefulness of photon beams as artistic primitives by detailing their use in a feature-length animated film.

The number of skyscrapers are increasing rapidly across the world. Interest is growing considerably in places such as Asia and Europe. Because of their height skyscrapers have a strong symbolic value and can help a city attract interest. In Sweden the number of skyscraper projects have also seen a significant increase, though relatively few of them have eventually been built. One of the most spectacular examples were the two Tellus Towers that were planned in southern Stockholm. The highest tower would have been the highest residential building in all of Scandinavia. The project was canceled by the municipality because of its visual impact over areas considered to be of national interest as well as concern over shadows. Instead a new project was suggested consisting of seven smaller high rise buildings. The aim of this thesis is to examine whether groups of smaller high rise buildings have benefits over major skyscrapers regarding visual impact and shadows, by comparing the Tellus Towers to the new project. The program ArcGIS Pro has been used to create 3D models of both projects, whereby analysis tools have been used to analyze their effects on the surrounding built area which was downloaded as 3D models from Stockholm municipality's data portal as well as OpenStreetMap based 3D models from Esri. The results reveal that the new project will cast significantly more shadows than its predecessor would have done, while having a smaller visual impact.

The present thesis derived from a personal need to explore how daylight can shape the emotional state of users and consequently their indoor experience. As a lighting design student I appreciated even more the power that light and shadows have upon indoor experiences. To investigate this further, an experiment with five panels was conducted. Moreover, since daylight conditions vary according to the latitude the spaces were simulated in Sweden and Cyprus, and subjects from both locations participated in the experiment.  The results suggest that daylight distributed in horizontal, vertical and squared shapes evokes mainly pleasant or activating emotions. Circular shapes provoke pleasant feelings and the organic: unpleasant and deactivating. The outcome indicates that emotions, perception of light levels, light distribution and shadows can alter considerably among individuals from different latitudes. Participants from northern latitude perceived the space darker than those from southeastern latitude. Additionally, when the subjects felt happy in a space they perceived it brighter than other spaces. The analysis suggests a link between memories, familiarity and emotions. Lastly, the importance of considering preferences of different groups of users is emphasized.

No description available.