What makes an image photorealistic and how to pinpoint and understand how our mind interprets different elements in an image conditions? It is proposed that the phrase "imperfect makes perfect" is the key for the photorealistic goal in today’s 3D. There is a review of all the elements for the creation of one perfect image, such as Global Illumination, Anti-Aliasing and also a basic review of photography, how a scene is set up, color temperature and the nature of the real light. To put different theories to a test, the common three dimensional software 3D Studio Max was used with the V-Ray renderer. On a field trip to IKEA communications, we were assigned a project of a room scene containing a kitchen, with a finished scene model. A kitchen was created and experimented to reach a result where there is no visible difference between a computer generated image and the photography. Our result was not what we had hoped for due to many problems with our scene. We ourselves see this as a first step toward a scientific explanation to photorealism and what makes something photorealistic.

Este trabalho aborda a utilização de tecnologias para a criação de ambientes virtuais baseados em imagens, com uma aplicação na praça central da cidade de Pelotas/RS. Possibilita que o usuário realize interativamente um passeio no entorno da praça com recursos que permitem avaliações arquitetônicas e urbanísticas por meio de simulações de troca de cor nos prédios, inserção de novas construções e análise do estado de conservação de imóveis, com vantagens sobre métodos tradicionais de análises em montagens fotográficas estáticas. Enfatiza a pesquisa de soluções para visualização interativa de ambientes, focado na identificação de fontes de informação e não na sua modelagem matemática. Para a apresentação do trabalho, além da seleção das cenas urbanas que seriam estudadas, foram consideradas técnicas para a modelagem dos elementos arquitetônicos de forma que se obtivesse a máxima preservação das características naturais (estado de conservação, cores e riqueza de detalhes), formas para a visualização destes dados de maneira integrada com dados bibliográficos (histórico, técnicas construtivas e localização) e também a utilização de objetos multimídia para o enriquecimento na apresentação de conteúdos. Na busca de soluções, foram investigadas as técnicas de modelagem fotogramétrica como forma de obtenção de objetos realísticos com a manutenção das características do objeto original em modelos geométricos simplificados. Foram feitos estudos sobre as formas de apresentação de ambientes virtuais navegáveis através de panoramas interativos e também foi estudada uma forma de aproximar a visualização dos conteúdos com a visão natural humana, através da estereoscopia. O trabalho culmina com a fusão de todas as tecnologias estudadas em uma aplicação denominada “Praça República Virtual – PRV” (para resgatar o antigo nome da atual Praça Coronel Pedro Osório), que funciona como um canteiro de provas na medida que abre um leque de opções para utilização em estudos na área de Arquitetura e Urbanismo. / This work approaches the uses of technologies for creation of virtual environments based on images, with an application to the central square of the city of Pelotas/RS. It makes possible to the user to accomplish an interactive walkthrough with resources that allows architectural and urban planning evaluations through simulations of color changes in the buildings, insertion of new constructions and analysis of the conservation condition of the buildings, with advantages if compared to traditional methods of analysis with static photographic assemblies. It emphasizes the research of solutions for interactive visualization of environments, focused in the identification of sources of information and not in mathematical modeling. Besides the selection of the urban scenes to be studied, it was considered techniques for modeling the architectural elements to obtain the maximal preservation of their natural characteristics (conservation state, colors and wealth of details), ways of visualization of nowadays conservation, but integrated with bibliographical dates (historical, constructive techniques and location). It also includes the uses of multimedia objects to the presentation of contents. In the search of solutions, techniques of photogrammetric modeling were investigated, looking for the construction of realistic objects and maintenance of the characteristics of the original object but using simplified geometric models. It was done a search about forms of presentation of navigable virtual environments through interactive panoramas and also using a prototype of stereoscopy. The work culminates with the coalition of all studied technologies in a prototype of the central square of Pelotas called “Praça República Virtual–PRV” (to rescue the old name of the current Square Cel. Pedro Osório). It works like a stonemason of proofs in the measure that opens various options of use in studies in the area of Architecture and Urban Planning.

Point-based rendering methods have proven to be effective for the display of large point cloud surface models. For a realistic visualization of the models, transparency and shadows are essential features. We propose a method for point cloud rendering with transparency and shadows at interactive rates. Our approach does not require any global or local surface reconstruction method, but operates directly on the point cloud. All passes are executed in image space and no pre-computation steps are required. The underlying technique for our approach is a depth peeling method for point cloud surface representations. Having detected a sorted sequence of surface layers, they can be blended front to back with given opacity values to obtain renderings with transparency. These computation steps achieve interactive frame rates. For renderings with shadows, we determine a point cloud shadow texture that stores for each point of a point cloud whether it is lit by a given light source. The extraction of the layer of lit points is obtained using the depth peeling technique, again. For the shadow texture computation, we also apply a Monte-Carlo integration method to approximate light from an area light source, leading to soft shadows. Shadow computations for point light sources are executed at interactive frame rates. Shadow computations for area light sources are performed at interactive or near-interactive frame rates depending on the approximation quality.

Local Light Alignment is a new shading based technique in the field of shape depiction, a field which concerns itself with techniques to represent and enhance the three-dimensional (3D) shape of objects in two-dimensional (2D) visual media. The main idea of Local Light Alignment is to locally adjust the incoming direction of light to create contrast in a way that enhances the perception of shape and surface detail. It is aimed at visual artists and uses a multiple scale approach, where the user can tune the enhancement of geometric shapes of different sizes. Local Light Alignment was published together with a new objective metric for measuring shape depiction called the congruence score. This thesis strives to increase knowledge about both these new techniques by investigating how varying several parameters for Local Light Alignment affect the congruence score at different scales and strengths of enhancement. The parameters investigated are the range and spatial parameters for the bilateral filter in the scale space construction as well as the enhancement strength parameter of the main Local Light Alignment algorithm. The thesis also tries to identify any common visual characteristics for images that score high, to give a better intuition of what the congruence score represents. The tests are performed using four models, each representing a different field of application. For each model, several viewpoints are tested, and for every viewpoint, 244 differently parameterized renders are produced and scored. The results notably show that the spatial and range parameters both affect controllability of the algorithm by shifting the scores toward the finer end of the scale space with higher values, without affecting the total score. The enhancement strength parameter is shown to affect the congruence score positively, but with diminishing returns as values approach 1. It is also shown by example that the images showing the largest improvement in congruence score tend to exhibit such high degrees of exaggeration that they would probably not be considered good examples of shape depiction by human standards. This is identified as an interesting area to perform subjective evaluations in future research. These investigations will be valuable to those who will create application software that features Local Light Alignment, as well as those wanting to employ the congruence score metric. / Local Light Alignment är en ny skuggningsbaserad teknik inom området formskildring, ett område som är befattar sig med olika tekniker för att förbättra den tredimensionella formåtergivningen av objekt i tvådimensionella medier. Huvudidén bakom Local Light Alignment är att lokalt justera riktningen av inkommande ljus på ett sätt som skapar ytterligare kontrast och förstärker uppfattningen av form och ytdetaljer. Tekniken riktar sig mot designers och använder sig av en flerskalig approach, där användaren kan justera förbättringen av geometriska former av olika storlekar. Local Light Alignment publicerades tillsammans med en kvantitativ metrik för att mäta formskildring, kallad ”congruence score”, eller kongruenspoängtal på svenska. Denna uppsats eftersträvar att öka kunskapen kring båda dessa nya tekniker genom att undersöka hur parameterrymden för Local Light Alignment påverkar kongruenspoängtalet vid olika skalor och förbättringsstyrkor. De undersökta parametrarna är omfångs- och spatialparametrarna som tillhör det bilaterala filtret som används i konstruktionen av skal-rymden, samt parametern för förbättringsstyrka tillhörandes den centrala delen av Local Light Alignment algoritmen. Upptatsen försöker också att identifiera gemensamma visuella uttryck för bilder som visar stor förbättring i kongruenspängtalet, för att kunna ge en intuition om vad kongruenspoängtalet representerar som modell. Studien är genomförd med 4 olika 3D-modeller, där varje modell representerar ett separat område där Local Light Alignment skulle kunna användas. För varje modell så undersöks flera åskådningsvinklar, och för varje åskådningsvinkel så produceras 244 olika parameteriserade renderingar som sedan utvärderas med kongruenspoängtal. Resultaten visar att omfångs- och spatialparametrarna båda påverkar kontrollerbarheten hos algoritmen genom att skifta massan av poäng från den grövre delen av skal-rymden, mot den finare. Detta utan att nämnvärt påverka totalpoängen. Förbättrinsstyrkeparametern visas påverkar kongruenspoängtalet positivt, men med avtagande effect då värdet närmar sig 1. Det demonstreras också visuellt hur de bilder som visar störst förbättring i kongruenspoängtal också uppvisar så höga nivåer av överdriftseffekter att de knappast kan anses vara goda exempel av förbättrad formskildring. Detta identifieras som en intressant riktning för framtida forskning med stöd av subjektiva utvärderingar.

Gegenstand der vorliegenden Dissertation ist die Entwicklung von Algorithmen und Methoden mit dem Ziel, Archäologen bei der täglichen wissenschaftlichen Arbeit zu unterstützen. Im Teil I werden Ideen präsentiert, mit denen sich die extrem zeitintensive und stellenweise stupide Funddokumentation beschleunigen lässt. Es wird argumentiert, dass das dreidimensionale Erfassen der Fundobjekte mittels Laser- oder Streifenlichtscannern trotz hoher Anschaffungskosten wirtschaftlich und vor allem qualitativ attraktiv ist. Mithilfe von nicht fotorealistischen Visualisierungstechniken können dann wieder aussagekräftige, aber dennoch objektive Bilder generiert werden. Außerdem ist speziell für Gefäße eine vollautomatische und umfassende Merkmalserhebung möglich. Im II. Teil gehen wir auf das Problem der automatisierten Gefäßklassifikation ein. Nach einer theoretischen Betrachtung des Typbegriffs in der Archäologie präsentieren wir eine Methodologie, in der Verfahren sowohl aus dem Bereich des unüberwachten als auch des überwachten Lernens zum Einsatz kommen. Besonders die letzteren haben sich dabei als überaus praktikabel erwiesen, um einerseits unbekanntes Material einer bestehenden Typologie zuzuordnen, andererseits aber auch die Struktur der Typologie selbst kritisch zu hinterfragen. Sämtliche Untersuchungen haben wir beispielhaft an den bronzezeitlichen Gräberfeldern von Kötitz, Altlommatzsch (beide Lkr. Meißen), Niederkaina (Lkr. Bautzen) und Tornow (Lkr. Oberspreewald-Lausitz) durchgeführt und waren schließlich sogar in der Lage, archäologisch relevante Zusammenhänge zwischen diesen Fundkomplexen herzustellen. / The topic of the dissertation at hand is the development of algorithms and methods aiming at supporting the daily scientific work of archaeologists. Part I covers ideas for accelerating the extremely time-consuming and often tedious documentation of finds. It is argued that digitizing the objects with 3D laser or structured light scanners is economically reasonable and above all of high quality, even though those systems are still quite expensive. Using advanced non-photorealistic visualization techniques, meaningful but at the same time objective pictures can be generated from the virtual models. Moreover, specifically for vessels a fully-automatic and comprehensive feature extraction is possible. In Part II, we deal with the problem of automated vessel classification. After a theoretical consideration of the type concept in archaeology we present a methodology, which employs approaches from the fields of both unsupervised and supervised machine learning. Particularly the latter have proven to be very valuable in order to assign unknown entities to an already existing typology, but also to challenge the typology structure itself. All the analyses have been exemplified by the Bronze Age cemeteries of Kötitz, Altlommatzsch (both district of Meißen), Niederkaina (district of Bautzen), and Tornow (district Oberspreewald-Lausitz). Finally, we were even able to discover archaeologically relevant relationships between these sites.

Drawing sketches is certainly one of the most important but at the same time elaborate parts of archaeological work. Currently, 3D scanning technology is affording a number of new applications, and only one of them is using virtual copies instead of the originals as the basis for documentation. Our major contribution are methods for automatically generating stylized images from 3D models. These are not only intuitive and easy to read but also more objective and accurate than traditional drawings. Besides some other useful tools we show several examples from our daily work proving that the system accelerates the whole documentation process considerably.

In the early days of computer graphics, research was mainly driven by the goal to create realistic synthetic imagery. By contrast, non-photorealistic computer graphics, established as its own branch of computer graphics in the early 1990s, is mainly motivated by concepts and principles found in traditional art forms, such as painting, illustration, and graphic design, and it investigates concepts and techniques that abstract from reality using expressive, stylized, or illustrative rendering techniques. This thesis focuses on the artistic stylization of two-dimensional content and presents several novel automatic techniques for the creation of simplified stylistic illustrations from color images, video, and 3D renderings. Primary innovation of these novel techniques is that they utilize the smooth structure tensor as a simple and efficient way to obtain information about the local structure of an image. More specifically, this thesis contributes to knowledge in this field in the following ways. First, a comprehensive review of the structure tensor is provided. In particular, different methods for integrating the minor eigenvector field of the smoothed structure tensor are developed, and the superiority of the smoothed structure tensor over the popular edge tangent flow is demonstrated. Second, separable implementations of the popular bilateral and difference of Gaussians filters that adapt to the local structure are presented. These filters avoid artifacts while being computationally highly efficient. Taken together, both provide an effective way to create a cartoon-style effect. Third, a generalization of the Kuwahara filter is presented that avoids artifacts by adapting the shape, scale, and orientation of the filter to the local structure. This causes directional image features to be better preserved and emphasized, resulting in overall sharper edges and a more feature-abiding painterly effect. In addition to the single-scale variant, a multi-scale variant is presented, which is capable of performing a highly aggressive abstraction. Fourth, a technique that builds upon the idea of combining flow-guided smoothing with shock filtering is presented, allowing for an aggressive exaggeration and an emphasis of directional image features. All presented techniques are suitable for temporally coherent per-frame filtering of video or dynamic 3D renderings, without requiring expensive extra processing, such as optical flow. Moreover, they can be efficiently implemented to process content in real-time on a GPU. / In den Anfängen der Computergrafik war die Forschung hauptsächlich von dem Anspruch getragen, realistisch aussehende synthetische Bilder zu erstellen. Im Gegensatz dazu ist die nicht-photorealistische Computergraphik, ein Untergebiet der Computergrafik, welches in den frühen 1990er Jahren gegründet wurde, vor allem motiviert durch Konzepte und Prinzipien der traditionellen Kunst wie Malerei, Illustration und Grafikdesign. Diese Arbeit beschäftigt sich mit der künstlerischen Verarbeitung von zweidimensionalen Bildinhalten und präsentiert mehrere neue automatische Verfahren für die Erstellung von vereinfachten künstlerischen Darstellungen von Farbbildern, Videos und 3D- Renderings. Wichtigste Neuerung dieser Techniken ist die Verwendung des Strukturtensors als eine einfache und effiziente Möglichkeit, Informationen über die lokale Struktur eines Bildes zu erhalten. Konkret werden die folgenden Beiträge gemacht. Erstens wird eine umfassende übersicht über den Strukturtensor gegeben. Insbesondere werden verschiedene Methoden für die Integration des kleineren Eigenvektorfeldes des geglätteten Strukturtensors entwickelt, und die Überlegenheit des geglätteten Strukturtensors gegenüber dem populären Edge-Tangent-Flow demonstriert. Zweitens werden separable Implementierungen des bilateralen Filters und des Difference of Gaussians Filters vorgestellt. Durch die Anpassung der Filter an die lokale Struktur des Bildes werden Bildfehler vermieden, wobei der Vorgang rechnerisch effizient bleibt. Zusammengenommen bieten beide Techniken eine effektive Möglichkeit, um einen Cartoon-ähnlichen Effekt zu erzielen. Drittens wird eine Verallgemeinerung des Kuwahara-Filters vorgestellt. Durch die Anpassung von Form, Umfang und Orientierung der Filter an die lokale Struktur werden Bildfehler verhindert. Außerdem werden direktionale Bildmerkmale besser berücksichtigt und betont, was zu schärferen Kanten und einem malerischen Effekt führt. Neben der single-scale Variante wird auch eine multi-scale Variante vorgestellt, welche im Stande ist, eine höhere Abstraktion zu erzielen. Viertens wird eine Technik vorgestellt, die auf der Kombination von flussgesteuerter Glättung und Schock-Filterung beruht, was zu einer intensiven Verstärkung und Betonung der direktionalen Bildmerkmale führt. Alle vorgestellten Techniken erlauben die zeitlich kohärente Verarbeitung von Einzelbildern eines Videos oder einer dynamischen 3D-Szene, ohne dass andere aufwendige Verfahren wie zum Beispiel die Berechnung des optischen Flusses, benötigt werden. Darüberhinaus können die Techniken effizient implementiert werden und ermöglichen die Verarbeitung in Echtzeit auf einem Grafikprozessor (GPU).

In dieser Dissertation wird erstmalig ein theoretisches Fundament zur Beschneiung virtueller Szenen entwickelt. Das theoretische Fundament wird als analytisches Modell in Form einer Diffusionsgleichung formuliert. Aus dem analytischen Modell lässt sich eine Gruppe von Algorithmen zur Beschneiung virtueller Szenen ableiten. Eingehende Voruntersuchungen zur allgemeinen Modellierung natürlicher Phänomene in der Computergraphik sowie eine Klassifikation der bestehenden Literatur über mathematische Schneemodellierung bilden den Anfang der Arbeit. Aus der umfassenden Darstellung der Eigenschaften von Schnee, wie er in der Natur vorkommt, ergeben sich die Grundlagen für die Modellbildung. Die Modellbildung fußt auf den grundlegenden Ansätzen der klassischen Mechanik und der statistischen Physik. Für die Beschneiung auf visueller Skala erweist sich der Diffusionsprozess als geeignete Beschreibung. Mit der Beschreibung lassen sich diffusiv Schneeoberflächen erzeugen. Der konkrete computergraphische Wert des theoretischen Fundaments wird anhand zweier Implementierungen exemplarisch dargestellt, und zwar in der Distanzfeldmethode und der Diffusionskernmethode. Die Ergebnisse werden mithilfe dreidimensionaler Rauschtexturen und Alpha-Masken an den Rändern fotorealistisch visualisiert. / In this dissertation for the first time a theoretical foundation is developed for snow accumulation in virtual scenes. The theoretical foundation is formulated in an analytical model as diffusion equation. The analytical model leads to a group of algorithms for virtual snow accumulation. Comprehensive investigations for the modelling of natural phenomena in computer graphics in general are used to develop a method classification scheme. Another classification is given for an overview over the aspects of snow in the real world. This allows an efficient presentation of related literature on snow modelling. A new approach of snow modelling is then drawn from first principles of classical mechanics and statistical physics. Diffusion processes provide an efficient theoretical framework for snow accumulation. The mathematical structure of diffusion equations is discussed and demonstrated to be adequate to snow modelling in visual scales. The value of the theoretical foundation for computer graphics is demonstrated with two exemplary implementations, a distance field method and the diffusion kernel method. Results are visualized with 3D noise textures and alpha masks near borders delivering photorealistic snow pictures.

浮雕是雕刻藝術中重要的表現方法，藉由在平板上雕刻出高低落差，傳達出豐富的形狀視覺線索，是介於3D雕塑和2D畫作中間的一種物體外形的表現方式。本論文將針對淺浮雕這類型相對高度較低的浮雕技法，將要表達的3D場景壓縮到接近平面但盡可能保留細節。我們使用適應性直方圖均衡化技術去壓縮高度的動態範圍並盡可能強化細節，且經由降低取樣點數量的技巧加速適應性直方圖均衡化的計算，以利於使用者進行互動性自訂風格化。另外依照場景特徵的流向，增加特殊的刻紋去豐富淺浮雕的風格表現。 / Relief is a sculptural technique to express the shape feature on a flat surface. It is an art medium between 3D sculpture and 2D painting. In this thesis, we focus on bas-relief, which is a relatively low relief to compress the depth of 3D scene to a shallow overall depth and preserve details of the shape. We use the adaptive histogram equalization (AHE) to compress the depth range and enhance details, and accelerate the AHE computation by sample reduction, which is in favor of the user interaction of custom stylization. Furthermore, adding special carving patterns according to feature flows of the scene enriches the stylization of the relief generation.

The aim of this thesis is non-realistic video rendering. It starts with a summary of existing techniques and then this thesis concentrates on selected methods that are able to work in real-time. To process video more effectivelly, we use accelleration on graphical processing unit with usage of OpenGL and GLSL.