Shadows contribute significantly to the perceived realism of an image, and provide an important depth cue. Rendering high quality, antialiased shadows efficiently is a difficult problem. To antialias shadows, it is necessary to compute partial visibilities, but computing these visibilities using existing approaches is often too slow for interactive applications. Shadow maps are a widely used technique for real-time shadow rendering. One major drawback of shadow maps is aliasing, because the shadow map data cannot be filtered in the same way as colour textures. In this thesis, I present variance shadow maps (VSMs). Variance shadow maps use a linear representation of the depth distributions in the shadow map, which enables the use of standard linear texture filtering algorithms. Thus VSMs can address the problem of shadow aliasing using the same highly-tuned mechanisms that are available for colour images. Given the mean and variance of the depth distribution, Chebyshev's inequality provides an upper bound on the fraction of a shaded fragment that is occluded, and I show that this bound often provides a good approximation to the true partial occlusion. For more difficult cases, I show that warping the depth distribution can produce multiple bounds, some tighter than others. Based on this insight, I present layered variance shadow maps, a scalable generalization of variance shadow maps that partitions the depth distribution into multiple segments. This reduces or eliminates an artifact - "light bleeding" - that can appear when using the simpler version of variance shadow maps. Additionally, I demonstrate exponential variance shadow maps, which combine moments computed from two exponentially-warped depth distributions. Using this approach, high quality results are produced at a fraction of the storage cost of layered variance shadow maps. These algorithms are easy to implement on current graphics hardware and provide efficient, scalable solutions to the problem of shadow map aliasing.

Three dimensional (3D) shape reconstruction that aims to reconstruct 3D surface of objects using acquired images, is one of the main problems in computer vision. There are many applications of 3D shape reconstruction, from satellite imaging to material sciences, considering a continent on earth or microscopic surface properties of a material. One of these applications is the automated firearm identification that is an old, yet an unsolved problem in forensic science. Firearm evidence matching algorithms rely on the fact that a firearm creates characteristic marks on surfaces of the bullets and the cartridge cases. These marks should be digitized unaffected from different surface material properties of evidences. Accuracy of 3D shape is one of the most important parameters affecting the overall identification performance. A very high resolution, accurate 3D data have to be reconstructed in the order of minutes. Photometric stereo (PS) method is capable of reconstructing high resolution surfaces in a fast manner. But, the metallic material and the surface topology of the firearm evidences generate highlights and shadows on their images that does not comply with the assumptions of conventional PS. In the scope of this work, it is intended to design an accurate, fast and robust 3D shape reconstruction scheme using PS considering highlights and shadows. These new PS procedures to be developed here should not be limited only to the ballistic evidences but they also could be used for a wider range of objects reflection properties and texture. For this purpose, masked PS methods which are quite fast when compared to other approaches, were classified and implemented. Simple additional masking methods are also proposed. A novel weighted PS method, using weighted least square estimation, is presented to eliminate false edges created by the masks. Concurrently, the calibration processes and the illumination configuration were improved. The disturbances due to close light sources were removed by image calibrations. From experimental tests to simulate the light positioning problem, it is concluded that the double zenith illumination configuration have better performance than the optimal single zenith illumination configuration, when the highlights and the shadows are considered. Double zenith illumination configuration results were further improved by the weighted normal PS with a small additional computation cost. All the implemented methods were tested firstly on the controlled environment using synthetic images. Later the same tests were conducted on real objects with varying characteristics as well as the firearm evidences.

A fundamental operation in computer graphics is to determine for a given point and direction in a scene, which geometric surface is nearest this point from this direction and thus visible. Conceptually, the point and direction define a "ray". Z-buffer hardware can compute surface visibility for a set of rays with a common origin (i.e. eye point) and a regular pattern of directions in real-time. However, this hardware is much less efficient at performing other visibility computations such as those required to accurately render shadows. A more flexible solution to the visible surface problem is needed. This work introduces the irregular Z-buffer algorithm, which efficiently solves the visible surface problem for rays with a common origin and arbitrary directions. In addition, we identify several changes to classical graphics architectures needed for hardware acceleration of this algorithm. Though these modifications are incremental in nature (i.e. no new functional units are introduced), we show that they enable significant new capability. In tandem with the irregular Z-buffer algorithm, a GPU with these changes has applications in: shadow rendering, indirect illumination, frameless rendering, adaptive anti-aliasing, adaptive textures, and jittered sampling. We explore the performance of hard and soft shadow rendering in particular, by way of a detailed hardware simulator. / text

Swiss psychoanalyst Carl Gustav Jung describes the encounter with the archetype of the shadow as the initial step to be taken by any individual seeking to initiate the individuation process. Jung observes a close relationship between this process and religion, suggesting that a psychologically beneficial religion can help guide the subject through individuation. Yet Jung finds few existing religious traditions that satisfy his criteria. Wicca, a neopagan religion popular in Europe and North America, presents itself at times as consciously psychological, striving to lead the practitioner to a goal of self-transformation, yielding a product that strangely resembles the individuated person. The objective therefore becomes not to criticize Wiccan religious claims, nor to deconstruct Jungian philosophy, but to identify the points of intersection between Wiccan theology/theology and Jungian psychology of religion, with a particular emphasis on the archetype of the shadow.

Shadows provide an important cue in computer graphics. In this thesis we focus on real-time soft shadow algorithms. Two new techniques are presented, both run entirely on modern graphics hardware. "Soft Shadows Using Precomputed Visibility Distance Functions" renders fake soft shadows in static scenes using precomputed visibility information. The technique handles dynamic local light sources and contains special computation steps to generate smooth shadows from hard visibility functions. The resulting images are not physically accurate, nevertheless the method renders plausible images that imitate global illumination. "Soft Projected Shadows" is a simple method for simulating natural shadow penumbra for projected grayscale shadow textures. Shadow blurring is performed entirely in image space and needs only a couple of special blurring passes on pixel shader 2.0 hardware. The technique treats shadow receivers as nearly planar surfaces and doesn’t handle self shadowing, but executes very fast and renders plausible soft shadows. Multiple overlapping shadow casters in a single shadow map are natively supported without any performance overhead.

Den här rapporten fokuserar på att ta fram en grund i hur skapandet av spelvegetation med polygonplan som korsar varandra kan göras, utan att få problem med oönskade artefakter och skuggor. Det finns givetvis flertalet metoder för att lösa detta som varierar beroende på vilken typ av ljussättning som implementerats i spelet samt vilken spelmotor som används. I den här undersökningen kommer endast en spelmotor med grund ljussättning användas.Målet var att undersöka flertalet metoder för att nå det önskade resultatet, vilket var fungerande spelvegetation med korsande polygonplan utan några skuggor eller artefakter. Moment som inte ingick i den här undersökningen var ingående undersökningar i hur vertexnormaler fungerar på en mer matematisk nivå, samt hur dessa tekniker kan överföras till andra spelmotorer. För att uppnå dessa mål gjordes en del undersökningar i hur spelvegetations geometri och vertexnormaler påverkar resultatet, samt materialinställningar i den valda spelmotorn.Vikten av en klar bild av vilken typ av spelvegetation som ska skapas innan arbetet påbörjas visade sig tidigt i undersökningen. Organiska och mjuka former är att föredra, och det är även viktigt att kontrollera hur vertexnormalernas riktning påverkar objektet i den valda spelmotorn. I själva spelmotor är det materialet på objektet som har störst inverkan på resultatet, framförallt materialets underlagsfärg. Genom att följa dessa riktlinjer kan målet av spelvegetation, med korsande polygonplan, utan alltför tydliga skuggor och artefakter uppnås. / This report focuses on establishing a foundation in how to create game foliage with criss-crossing polygon planes, without getting unwanted artefacts or shadows. There are several different methods to achieve this depending on what kind of lighting the game has implemented, but also which game engine is being used. In this research, only one game engine with basic lighting will be used.The goal was to research several different methods that would give the desired result, which as stated above, was to create working game assets with criss-crossing polygon planes without artefacts. Stages that are not included in this research are how vertex normals work from a mathematics perspective, and how these methods would work in other game engines. Research was focused on how geometry and vertex normals affect the object visual appearance, as well as the impact the material settings in the games engine provided.The survey quickly showed the importance of having a clear vision on what type of game foliage was sought to be created before the work began. Organic and soft shapes are preferred, and it is also important to check how the vertex normals affect the object in the selected game engine. In the game engine itself, it is the material on the object that has the greatest impact on the result, especially the material's subsurface colour. By following these guidelines, the goal was achieving game foliage with less visible shadows and artefact.

Windows provide building occupants with important physiological and psychological benefits but are absent from many indoor spaces. It is argued that most existing attempts at compensating for an absence of windows fall short because they lack either outdoor environmental information or sensory stimulation. A wind-animated digital-tree shadow was used to test this hypothesis. The work concludes that the following strategies are likely to help most to compensate for an absence of windows: (1) establishing a live connection with the outdoors; (2) introducing controllable sensory variation into a space; (3) making such change a source of natural environmental information. It is suggested that these approaches could be helpful used either separately or in combinations but that a live connection with the outdoors that introduces controllable naturally-generated change into a space would likely be most effective. The video files that accompany this thesis show the digital shadow with wind and computer generated movement.

Um dos algoritmos para cálculo de sombras mais eficientes existentes atualmente é o Shadow Mapping de Williams. Ele é simples, robusto e facilmente mapeável para o hardware gráfico existente. Este algoritmo conta com duas etapas. A primeira é responsável pela geração de um depth buffer (Shadow Map) a partir do ponto de vista da luz. Na segunda etapa a imagem final da cena é gerada a partir do ponto de vista da câmera. De maneira a determinar se os pixels da imagem final estão iluminados ou em sombra, cada pixel é transformado para o espaço da luz e testado contra o Shadow Map. Shadow Maps tradicionais armazenam apenas um valor de profundidade por célula, fazendo com que os testes de sombra retornem valores binários. Isso pode ocasionar o surgimento de aliasing nas bordas das sombras. Este trabalho apresenta uma nova abordagem capaz de produzir melhores resultados de suavização que, em conjunto com o algoritmo de PCF (Percentage Closer Filtering), reduz o serrilhado das bordas das sombras através do uso de filtros de menor tamanho. O novo algoritmo estende os conceitos de Shadow Map e de teste de sombra de forma a suportarem múltiplos valores de profundidade. Esta nova abordagem apresenta potencial para implementação em hardware, e também pode ser implementada explorando a programabilidade das recentes placas gráficas. / William’s Shadow Mapping is one of the most efficient hard shadow algorithms. It is simple, robust and can be easily mapped to the actual grapics hardware. It is a two-pass technique. In the first pass a depth buffer (Shadow Map) is created from the light’s view point. In the second pass the final image is rendered from the camera’s view point. In order to decide whether each pixel in the camera’s view is lit or in shadow with respect to the light source, the pixel is transformed into the light space, and tested against the Shadow Map. Shadow maps store a single depth value per cell, leading to a binary outcome by the shadow test, and are prone to produce aliased shadow borders. This work presents a new approach that produces better estimates of shadow percentages and, in combination with percentage closer filtering (PCF), reduces aliasing artifacts using smaller kernel sizes. The new algorithm extends the notions of shadow map and shadow test to support the representation of multiple depth values per shadow map cell, as well as multi-valued shadow test. This new approach has the potential for hardware implementation, but can also be implemented exploiting the programmable capabilities of recent graphics cards.

Um dos algoritmos para cálculo de sombras mais eficientes existentes atualmente é o Shadow Mapping de Williams. Ele é simples, robusto e facilmente mapeável para o hardware gráfico existente. Este algoritmo conta com duas etapas. A primeira é responsável pela geração de um depth buffer (Shadow Map) a partir do ponto de vista da luz. Na segunda etapa a imagem final da cena é gerada a partir do ponto de vista da câmera. De maneira a determinar se os pixels da imagem final estão iluminados ou em sombra, cada pixel é transformado para o espaço da luz e testado contra o Shadow Map. Shadow Maps tradicionais armazenam apenas um valor de profundidade por célula, fazendo com que os testes de sombra retornem valores binários. Isso pode ocasionar o surgimento de aliasing nas bordas das sombras. Este trabalho apresenta uma nova abordagem capaz de produzir melhores resultados de suavização que, em conjunto com o algoritmo de PCF (Percentage Closer Filtering), reduz o serrilhado das bordas das sombras através do uso de filtros de menor tamanho. O novo algoritmo estende os conceitos de Shadow Map e de teste de sombra de forma a suportarem múltiplos valores de profundidade. Esta nova abordagem apresenta potencial para implementação em hardware, e também pode ser implementada explorando a programabilidade das recentes placas gráficas. / William’s Shadow Mapping is one of the most efficient hard shadow algorithms. It is simple, robust and can be easily mapped to the actual grapics hardware. It is a two-pass technique. In the first pass a depth buffer (Shadow Map) is created from the light’s view point. In the second pass the final image is rendered from the camera’s view point. In order to decide whether each pixel in the camera’s view is lit or in shadow with respect to the light source, the pixel is transformed into the light space, and tested against the Shadow Map. Shadow maps store a single depth value per cell, leading to a binary outcome by the shadow test, and are prone to produce aliased shadow borders. This work presents a new approach that produces better estimates of shadow percentages and, in combination with percentage closer filtering (PCF), reduces aliasing artifacts using smaller kernel sizes. The new algorithm extends the notions of shadow map and shadow test to support the representation of multiple depth values per shadow map cell, as well as multi-valued shadow test. This new approach has the potential for hardware implementation, but can also be implemented exploiting the programmable capabilities of recent graphics cards.

Made available in DSpace on 2014-06-11T19:22:26Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-04-20Bitstream added on 2014-06-13T18:47:37Z : No. of bitstreams: 1 fazan_aj_me_prud.pdf: 2364125 bytes, checksum: cd65fb05ed616ab1330e59a785328669 (MD5) / Este trabalho apresenta uma metodologia para a predição de sombras projetadas por edifícios em vias urbanas usando imagens aéreas de alta-resolução e modelos digitais de elevações (MDE). Elementos de sombra podem ser usados na modelagem de informação contextual para, por exemplo, a extração semi-automática ou automática da malha viária a partir de imagens aéreas ou de satélite, principalmente em áreas urbanas densas. O contexto modela as relações entre os objetos numa imagem, como por exemplo, as relações entre edifícios e vias adjacentes. O uso de conhecimento contextual tem se tornado cada vez mais comum em processos de análise de imagem, principalmente em se tratando de cenas complexas. Este trabalho foi inspirado nas atuais possibilidades de se obter modelos digitais de elevações densos e acurados de áreas urbanas complexas a partir de dados de sistemas aerotransportados de varredura a laser. A metodologia proposta consiste de três etapas seqüenciais. Primeiramente, os contornos de telhados de edifícios são extraídos manualmente a partir de uma imagem altimétrica obtida pela transformação do MDE/laser. De maneira similar, os contornos dos limites das vias são extraídos, agora a partir da imagem de intensidade de retorno do pulso laser. Na etapa seguinte, os polígonos dos contornos de telhado são projetados nas vias adjacentes através do uso da projeção paralela. A direção das retas de projeção paralela é calculada a partir de dados de efemérides solares e do instante de tomada da imagem aérea. Finalmente, as partes dos polígonos de sombra que estão livres de obstruções perspectivas de edifícios são determinadas a partir da separação das regiões afetadas pela perspectiva de tomada. / This research presents a methodology for prediction of building shadows cast on urban roads using high-resolution aerial images and Digital Elevation Models (DEM). Shadow elements can be used in the modeling of contextual information, as e. g., in the semiautomatic or automatic road network extraction from satellite or aerial images, mainly in dense urban areas. Context models the relations among objects in an image, as e. g., the relations among buildings and adjacent roads. The use of contextual knowledge has become more common in image analysis processes, mainly if complex scenes are present. This research drew inspiration from the present possibilities of obtaining accurate and dense DEM from airborne laser scanning data of complex urban areas. The proposed methodology consists in three sequential steps. First, the building roof contours are manually extracted from an intensity image generated from the laser DEM. In similar way, the road side contours are extracted, now from the radiometric information of the laser scanning data. Second, the roof contour polygons are projected onto the adjacent roads by using the parallel projection. The direction of the parallel straight lines is computed from the solar ephemeris, which depends on the taken time of the aerial photograph. Finally, the parts of shadow polygons that are freed of building perspective obstructions are determined, given rise to new shadow polygons.