Modelling and Visualisation of the Optical Properties of Cloth

Cloth and garment visualisations are widely used in fashion and interior design, entertaining, automotive and nautical industry and are indispensable elements of visual communication. Modern appearance models attempt to offer a complete solution for the visualisation of complex cloth properties. In the review part of the chapter, advanced methods that enable visualisation at micron resolution, methods used in three-dimensional (3D) visualisation workflow and methods used for research purposes are presented. Within the review, those methods offering a comprehensive approach and experiments on explicit clothes attributes that present specific optical phenomenon are analysed. The review of appearance models includes surface and image-based models, volumetric and explicit models. Each group is presented with the representative authors’ research group and the application and limitations of the methods. In the final part of the chapter, the visualisation of cloth specularity and porosity with an uneven surface is studied. The study and visualisation was performed using image data obtained with photography. The acquisition of structure information on a large scale namely enables the recording of structure irregularities that are very common on historical textiles, laces and also on artistic and experimental pieces of cloth. The contribution ends with the presentation of cloth visualised with the use of specular and alpha maps, which is the result of the image processing workflow

A radiative transfer framework for non-exponential media

We develop a new theory of volumetric light transport for media with non-exponential free-flight distributions. Recent insights from atmospheric sciences and neutron transport demonstrate that such distributions arise in the presence of correlated scatterers, which are naturally produced by processes such as cloud condensation and fractal-pattern formation. Our theory accommodates correlations by disentangling the concepts of the free-flight distribution and transmittance, which are equivalent when scatterers are statistically independent, but become distinct when correlations are present. Our theory results in a generalized path integral which allows us to handle non-exponential media using the full range of Monte Carlo rendering algorithms while enriching the range of achievable appearance. We propose parametric models for controlling the statistical correlations by leveraging work on stochastic processes, and we develop a method to combine such unresolved correlations (and the resulting non-exponential free-flight behavior) with explicitly modeled macroscopic heterogeneity. This provides a powerful authoring approach where artists can freely design the shape of the attenuation profile separately from the macroscopic heterogeneous density, while our theory provides a physically consistent interpretation in terms of a path space integral. We address important considerations for graphics including energy conservation, reciprocity, and bidirectional rendering algorithms, all in the presence of surfaces and correlated media

A Radiative Transfer Framework for Spatially-Correlated Materials

We introduce a non-exponential radiative framework that takes into account the local spatial correlation of scattering particles in a medium. Most previous works in graphics have ignored this, assuming uncorrelated media with a uniform, random local distribution of particles. However, positive and negative correlation lead to slower- and faster-than-exponential attenuation respectively, which cannot be predicted by the Beer-Lambert law. As our results show, this has a major effect on extinction, and thus appearance. From recent advances in neutron transport, we first introduce our Extended Generalized Boltzmann Equation, and develop a general framework for light transport in correlated media. We lift the limitations of the original formulation, including an analysis of the boundary conditions, and present a model suitable for computer graphics, based on optical properties of the media and statistical distributions of scatterers. In addition, we present an analytic expression for transmittance in the case of positive correlation, and show how to incorporate it efficiently into a Monte Carlo renderer. We show results with a wide range of both positive and negative correlation, and demonstrate the differences compared to classic light transport

Embroidery Modelling and Rendering

Embroidery is a traditional non-photorealistic art form in which threads of different colours stitched into a base material are used to create an image. This thesis presents techniques for automatically producing embroidery layouts from line drawings and for rendering those layouts in real time on potentially deformable 3D objects with hardware acceleration. Layout of stitches is based on automatic extraction of contours from line drawings followed by a set of stitch-placement procedures based on traditional embroidery techniques. Rendering first captures the lighting environment on the surface of the target object and renders it as an image in texture space. Stitches are rendered in this space using a lighting model suitable for threads at a resolution that avoids geometric and highlight aliasing. It is also possible to render stitches in layers to capture the 2.5D nature of embroidery. A filtered texture pyramid is constructed from the resulting texture and applied to the 3D object. Aliasing of fine stitch structure and highlights is avoided by this process. The result is a realistic embroidered image that properly responds to lighting

A Local Frequency Analysis of Light Scattering and Absorption

(presented at SIGGRAPH 2014)International audienceRendering participating media requires significant computation, but the effect of volumetric scattering is often eventually smooth. This article proposes an innovative analysis of absorption and scattering of local light fields in the Fourier domain and derives the corresponding set of operators on the covariance matrix of the power spectrum of the light field. This analysis brings an efficient prediction tool for the behavior of light along a light path in participating media. We leverage this analysis to derive proper frequency prediction metrics in 3D by combining per-light path information in the volume.We demonstrate the use of these metrics to significantly improve the convergence of a variety of existing methods for the simulation of multiple scattering in participating media. First, we propose an efficient computation of second derivatives of the fluence, to be used in methods like irradiance caching. Second, we derive proper filters and adaptive sample densities for image-space adaptive sampling and reconstruction. Third, we propose an adaptive sampling for the integration of scattered illumination to the camera. Finally, we improve the convergence of progressive photon beams by predicting where the radius of light gathering can stop decreasing. Light paths in participating media can be very complex. Our key contribution is to show that analyzing local light fields in the Fourier domain reveals the consistency of illumination in such media and provides a set of simple and useful rules to be used to accelerate existing global illumination methods.Une nouvelle analyse locale de la diffusion et de l'absorption de la lumière dans l'espace de Fourier est combinée avec le tracé de covariance et permet une estimation rapide du contenu fréquentiel local; cette approche permet l'amélioration de nombreux algorithmes de rendu de milieux participants tels que Progressive Photon Beams et l'integration d'effets de diffusion simple et l'échantillonnage et la reconstruction d'effets de simple diffusion simple en espace image

가상 의복의 생성, 수정 및 시뮬레이션을 위한 조작이 간편하고 문제를 발생시키지 않는 방법에 대한 연구

학위논문 (박사)-- 서울대학교 대학원 : 자연과학대학 협동과정 계산과학전공, 2016. 2. 고형석.This dissertation presents new methods for the construction, editing, and simulation of virtual garments. First, we describe a construction method called TAGCON, which constructs three-dimensional (3D) virtual garments from the given tagged and packed panels. Tagging and packing are performed by the user, and involve simple labeling and two-dimensional (2D) manipulation of the panelshowever, it does not involve any 3D manipulation. Then, TAGCON constructs the garment automatically by using algorithms that (1) position the panels at suitable locations around the body, and (2) find the matching seam lines and create the seam. We perform experiments using TAGCON to construct various types of garments. The proposed method significantly reduces the construction time and cumbersomeness. Secondly, we propose a method to edit virtual garments with synced 2D and 3D modification. The presented methods of linear interpolation, extrapolation, and penetration detection help users to edit the virtual garment interactively without the loss of 2D and 3D synchronization. After that, we propose a method to model the non-elastic components in the fabric stretch deformation in the context of developing physically based fabric simulator. We find that the above problem can be made tractable if we decompose the stretch deformation into the immediate elastic, viscoelastic, and plastic components. For the purpose of the simulator development, the decomposition must be possible at any stage of deformation and any occurrence of loading and unloading. Based on the observations of various constant force creep measurements, we make an assumption that, within a particular fabric, the viscoelastic and plastic components are proportional to each other and their ratio is invariant over time. Experimental results produced with the proposed method match with general expectations, and show that the method can represent the non-elastic stretch deformation for arbitrary time-varying force. In addition, we present a method to represent stylish elements of garments such as pleats and lapels. Experimental results show that the proposed method is effective at resolving problems that are not easily resolved using physically based cloth simulators.Chapter 1 Introduction 1 1.1 Digital Clothing 1 1.2 Garment Modeling 5 1.3 Physical Cloth Simulation 7 1.4 Dissertation Overview 9 Chapter 2 Previous Work 11 2.1 Garment Modeling 11 2.2 Physical Cloth Simulation 15 Chapter 3 Automatic Garment Construction from Pattern Analysis 17 3.1 Panel Classification 19 3.1.1 Panel Tagging 19 3.1.2 Panel Packing 22 3.1.3 Tagging-and-Packing Process 23 3.2 Classification of Seam-Line 24 3.3 Seam Creation 25 3.3.1 Creating the Intra-pack Seams 26 3.3.2 Creating the Inter-pack Seams 27 3.3.3 Creating the Inter-layer Seams 30 3.3.4 Seam-creation Process 31 3.4 Experiments 32 3.5 Conclusion 34 Chapter 4 Synced Garment Editing 39 4.1 Introduction to Synced Garment Editing 39 4.2 Geometric Approaches vs. Sensitivity Analysis 41 4.3 Trouble Free Synced Garment Editing 43 Chapter 5 Physically Based Non-Elastic Clothing Simulation 49 5.1 Classification of Deformation 50 5.2 Modeling Non-Elastic Deformations 53 5.2.1 Development of the Non-Elastic Model 55 5.2.2 Parameter Value Determination 60 5.3 Implementation 61 5.4 Experiments 65 Chapter 6 Tangle Avoidance with Pre-Folding 73 6.1 Problem of the First Frame Tangle 73 6.2 Tangle Avoidance with Pre-Folding 75 Chapter 7 Conclusion 81 Appendix A Simplification in the Decomposition of Stretch Deformation 85 Bibliography 87 초 록 99Docto

The asymmetries of colour constancy as determined through illumination discrimination using tuneable LED light sources

PhD ThesisThe light reflected from object surfaces changes with the spectral content of the illumination. Despite these changes, the human visual system tends to keep the colours of surfaces constant, a phenomenon known as colour constancy. Colour constancy is known to be imperfect under many conditions; however, it is unknown whether the underlying mechanisms present in the retina and the cortex are optimised for the illuminations under which they have evolved, namely, natural daylights, or for particular objects. A novel method of measuring colour constancy, by illumination discrimination, is presented and explored. This method, unlike previous methods of measuring colour constancy, allows the testing of multiple, real, illuminations with arbitrary spectral content, through the application of tuneable, multi-channel LED light sources. Data from both real scenes, under real illuminations, and computer simulations are presented which support the hypothesis that the visual system maintains higher levels of colour constancy for daylight illumination changes, and in particular in the “bluer” direction, which are also the changes most frequent in nature. The low-level cone inputs for various experimental scenes are examined which challenge all traditional theories of colour constancy supporting the conclusions that higher-level mechanisms of colour constancy are biased for particular illuminations. Furthermore, real and simulated neutral (grey) surfaces are shown to affect levels of colour constancy. Moreover, the conceptual framework for discussing colour constancy with respect to emergent LED light sources is discussed.EPSR

A radiative transfer framework for rendering materials with anisotropic structure

The radiative transfer framework that underlies all current rendering of volumes is limited to scattering media whose properties are invariant to rotation. Many systems allow for "anisotropic scattering," in the sense that scattered intensity depends on the scattering angle, but the standard equation assumes that the structure of the medium is isotropic. This limitation impedes physics-based rendering of volume models of cloth, hair, skin, and other important volumetric or translucent materials that do have anisotropic structure. This paper presents an end-to-end formulation of physics-based volume rendering of anisotropic scattering structures, allowing these materials to become full participants in global illumination simulations. We begin with a generalized radiative transfer equation, derived from scattering by oriented non-spherical particles. Within this framework, we propose a new volume scattering model analogous to the well-known family of microfacet surface reflection models; we derive an anisotropic diffusion approximation, including the weak form required for finite element solution and a way to compute the diffusion matrix from the parameters of the scattering model; and we also derive a new anisotropic dipole BSSRDF for anisotropic translucent materials. We demonstrate results from Monte Carlo, finite element, and dipole simulations. All these contributions are readily implemented in existing rendering systems for volumes and translucent materials, and they all reduce to the standard practice in the isotropic case.National Science Foundation (grants CCF-0347303 and CCF-0541105), Unilever Corporatio

Modelagem de aparência baseada em biofísica para tecidos do fígado humano

A representação gráfica de tecidos humanos é uma importante demanda para aplicações de áreas como ensino, entretenimento e treinamento médico. Frequentemente, a simulação de tais materiais envolve considerar características dinâmicas vinculadas as suas funções no corpo humano e que influenciam diretamente também em sua aparência. O fígado humano, apesar de um órgão interno, portanto, de difícil acesso, possui diferentes modelos de representação apresentados na literatura da Computação Gráfica (CG). Entretanto, tais modelos desconsideram as influências das propriedades ópticas dos elementos biofísicos que compõem os tecidos hepáticos, fornecendo assim, aproximações cuja parametrização controla apenas um estado específico do material orgânico, em geral, avaliando visualmente o resultado. O presente trabalho apresenta a modelagem dos tecidos do fígado humano através da descrição dos elementos biofísicos que compõem suas camadas estruturais: o parênquima e a cápsula de Glisson. Além disso, tal modelo implementa a interação luz-matéria em termos de eventos como a absorção, dispersão, reflexão e transmissão de luz, como processos biológicos que produzem a coloração específica do material, ou seja, sua resposta espectral. A abordagem matemática do modelo é definida como numérica e estocástica, para a qual é apresentada uma solução para garantir sua convergência. Reunindo recentes descrições sobre a estrutura dos tecidos hepáticos e sua interação com a luz apresentadas na literatura biomédica, o modelo desenvolvido representa a primeira solução baseada em biofísica para um órgão interno do corpo humano. Os resultados de imagens geradas através do modelo são apresentados junto a fotografias de tecidos análogos, assim como, curvas de respostas espectrais e espaciais disponíveis na literatura biomédica são comparadas com as produzidas pelo modelo desenvolvido, evidenciando a capacidade deste na representação gráfica do tecido hepático

Computational Light Transport for Forward and Inverse Problems.

El transporte de luz computacional comprende todas las técnicas usadas para calcular el flujo de luz en una escena virtual. Su uso es ubicuo en distintas aplicaciones, desde entretenimiento y publicidad, hasta diseño de producto, ingeniería y arquitectura, incluyendo el generar datos validados para técnicas basadas en imagen por ordenador. Sin embargo, simular el transporte de luz de manera precisa es un proceso costoso. Como consecuencia, hay que establecer un balance entre la fidelidad de la simulación física y su coste computacional. Por ejemplo, es común asumir óptica geométrica o una velocidad de propagación de la luz infinita, o simplificar los modelos de reflectancia ignorando ciertos fenómenos. En esta tesis introducimos varias contribuciones a la simulación del transporte de luz, dirigidas tanto a mejorar la eficiencia del cálculo de la misma, como a expandir el rango de sus aplicaciones prácticas. Prestamos especial atención a remover la asunción de una velocidad de propagación infinita, generalizando el transporte de luz a su estado transitorio. Respecto a la mejora de eficiencia, presentamos un método para calcular el flujo de luz que incide directamente desde luminarias en un sistema de generación de imágenes por Monte Carlo, reduciendo significativamente la variancia de las imágenes resultantes usando el mismo tiempo de ejecución. Asimismo, introducimos una técnica basada en estimación de densidad en el estado transitorio, que permite reusar mejor las muestras temporales en un medio parcipativo. En el dominio de las aplicaciones, también introducimos dos nuevos usos del transporte de luz: Un modelo para simular un tipo especial de pigmentos gonicromáticos que exhiben apariencia perlescente, con el objetivo de proveer una forma de edición intuitiva para manufactura, y una técnica de imagen sin línea de visión directa usando información del tiempo de vuelo de la luz, construida sobre un modelo de propagación de la luz basado en ondas.<br /