102 research outputs found

    Surface Curvature Effects on Reflectance from Translucent Materials

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    Most of the physically based techniques for rendering translucent objects use the diffusion theory of light scattering in turbid media. The widely used dipole diffusion model (Jensen et al. 2001) applies the diffusion-theory formula derived for a planar interface to objects of arbitrary shapes. This paper presents first results of our investigation of how surface curvature affects the diffuse reflectance from translucent materials.Comment: 10 pages, 2 figures. The first version of this paper was published in the Communication Papers Proceedings of 18th International Conference on Computer Graphics, Visualization and Computer Vision 2010 - WSCG201

    Light Simulation with Participating Media

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    In this project we address the problem of light scattering in participating materials. We create a complete simulation of this phenomenon in a more general case than previous work. We analyse the directional part of light, in order to install a clear basis for future work. We derive two models from this analysis: the spherical Gaussians approximation and the double exponential approximation. These models are placed in the scope of the planned development of an improved method for scattering. We also code a custom ray tracer to have a complete pipeline of rendering and to understand the underneath concepts. The validation of our simulation is done by comparing against the results of Eugene d'Eon in his article of Quantized-diffusion.Dans ce projet, nous abordons le problème de la diffusion de la lumière dans des matériaux participant. Nous créons une simulation complète de ce phénomène dans un cas plus général que les travaux précédents. Nous analysons la partie directionnelle de la lumière, dans le but d'installer une base claire à de futurs travaux. Nous tirons deux modèles de cette analyse : l'approximation de gaussiennes sphériques et l'approximation de double exponentielle. Ces modèles sont placés dans le cadre de l'élaboration prévue d'une méthode amélioré pour la diffusion. Nous codons également un lanceur de rayons dans le but d'avoir un pipeline complet de rendu et de comprendre les concepts sous-jacents. La validation de notre simulation est effectuée en comparant avec les résultats de Eugene d'Eon dans son article Quantized-diffusion

    Directional Dipole Model for Subsurface Scattering

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    Perception based heterogeneous subsurface scattering for film

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    Many real world materials exhibit complex subsurface scattering of light. This internal light interaction creates the perception of translucency for the human visual system. Translucent materials and simulation of the subsurface scattering of light has become an expected necessity for generating warmth and realism in computer generated imagery. The light transport within heterogenous materials, such as marble, has proved challenging to model and render. The current material models available to digital artists have been limited to homogeneous subsurface scattering despite a few publications documenting success at simulating heterogeneous light transport. While the publications successfully simulate this complex phenomenon, the material descriptions have been highly specialized and far from intuitive. By combining the measurable properties of heterogeneous translucent materials with the defining properties of translucency, as perceived by the human visual system, a description of heterogeneous translucent materials that is suitable for artist use in a film production pipeline can be achieved. Development of the material description focuses on integration with the film pipeline, ease of use, and reasonable approximation of heterogeneous translucency based on perception. Methods of material manipulation are explored to determine which properties should be modifiable by artists while maintaining the perception of heterogenous translucency

    The Impact of Surface Normals on Appearance

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    The appearance of an object is the result of complex light interaction with the object. Beyond the basic interplay between incident light and the object\u27s material, a multitude of physical events occur between this illumination and the microgeometry at the point of incidence, and also beneath the surface. A given object, made as smooth and opaque as possible, will have a completely different appearance if either one of these attributes - amount of surface mesostructure (small-scale surface orientation) or translucency - is altered. Indeed, while they are not always readily perceptible, the small-scale features of an object are as important to its appearance as its material properties. Moreover, surface mesostructure and translucency are inextricably linked in an overall effect on appearance. In this dissertation, we present several studies examining the importance of surface mesostructure (small-scale surface orientation) and translucency on an object\u27s appearance. First, we present an empirical study that establishes how poorly a mesostructure estimation technique can perform when translucent objects are used as input. We investigate the two major factors in determining an object\u27s translucency: mean free path and scattering albedo. We exhaustively vary the settings of these parameters within realistic bounds, examining the subsequent blurring effect on the output of a common shape estimation technique, photometric stereo. Based on our findings, we identify a dramatic effect that the input of a translucent material has on the quality of the resultant estimated mesostructure. In the next project, we discuss an optimization technique for both refining estimated surface orientation of translucent objects and determining the reflectance characteristics of the underlying material. For a globally planar object, we use simulation and real measurements to show that the blurring effect on normals that was observed in the previous study can be recovered. The key to this is the observation that the normalization factor for recovered normals is proportional to the error on the accuracy of the blur kernel created from estimated translucency parameters. Finally, we frame the study of the impact of surface normals in a practical, image-based context. We discuss our low-overhead, editing tool for natural images that enables the user to edit surface mesostructure while the system automatically updates the appearance in the natural image. Because a single photograph captures an instant of the incredibly complex interaction of light and an object, there is a wealth of information to extract from a photograph. Given a photograph of an object in natural lighting, we allow mesostructure edits and infer any missing reflectance information in a realistically plausible way

    An emperical model for heterogeneous translucent objects

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    We introduce an empirical model for multiple scattering in heterogeneous translucent objects for which classical approximations such as the dipole approximation to the di usion equation are no longer valid. Motivated by the exponential fall-o of scattered intensity with distance, di use subsurface scattering is represented as a sum of exponentials per surface point plus a modulation texture. Modeling quality can be improved by using an anisotropic model where exponential parameters are determined per surface location and scattering direction. We validate the scattering model for a set of planar object samples which were recorded under controlled conditions and quantify the modeling error. Furthermore, several translucent objects with complex geometry are captured and compared to the real object under similar illumination conditions

    Exploration of Mouth Shading and Lighting in CG Production

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    The lighting and shading of human teeth in current computer animation features and live-action movies with effects are often intentionally avoided or processed by simple methods since they interact with light in complex ways through their intricate layered structure. The semi-translucent appearance of natural human teeth which result from subsurface scattering is difficult to replicate in synthetic scenes, though two techniques are often implemented. The first technique is to create an anatomically correct layered model, and render the teeth with both theoretically and empirically derived optical parameters of human teeth using physical subsurface materials. The second technique largely takes advantage of visual cheating, achieved by irradiance blending of finely painted textures. The result visually confirms that for most situations, non-physically based shading can yield believable rendered teeth by finely controlling contribution layers. In particular situations, such as an extremely close shot of a mouth, however, a physically correct shading model is necessary to produce highly translucent and realistic teeth

    Rendering Techniques in 3D Computer Graphics Based on Changes in the Brightness of the Object Background

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    Maintaining accurate colour constancy and constant colour appearance are only a few challenges one must conquer in a modern day digital three‐dimensional (3D) production. Many different factors influence the reproduction of colour in 3D rendering and one of the most important is certainly rendering engines. In our research, we have studied rendering of colours with three rendering engines (Blender Render, Cycles and Yafaray) of an open source 3D creation suite based on changes in the brightness of the object background from 20 to 80%. In one of these cases, colour of the object was adapted to the lighter background using the colour appearance model CIECAM02. With the analysis of colour differences, lightness and chroma between colours rendered using different rendering engines; we found out that rendering engines differently interpret colour, although the RGB values of colours and scene parameters were the same. Differences were particularly evident when rendering engine Cycles was used. However, Cycles also takes into account the object background. Numerical results of such research provide findings, which relate to the respective environment, and also these certainly demonstrate the successful implementation of the colour appearance model CIECAM02 in the 3D technologies and, in our opinion to other software packages for 3D computer graphics

    Enhancing Mesh Deformation Realism: Dynamic Mesostructure Detailing and Procedural Microstructure Synthesis

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    Propomos uma solução para gerar dados de mapas de relevo dinâmicos para simular deformações em superfícies macias, com foco na pele humana. A solução incorpora a simulação de rugas ao nível mesoestrutural e utiliza texturas procedurais para adicionar detalhes de microestrutura estáticos. Oferece flexibilidade além da pele humana, permitindo a geração de padrões que imitam deformações em outros materiais macios, como couro, durante a animação. As soluções existentes para simular rugas e pistas de deformação frequentemente dependem de hardware especializado, que é dispendioso e de difícil acesso. Além disso, depender exclusivamente de dados capturados limita a direção artística e dificulta a adaptação a mudanças. Em contraste, a solução proposta permite a síntese dinâmica de texturas que se adaptam às deformações subjacentes da malha de forma fisicamente plausível. Vários métodos foram explorados para sintetizar rugas diretamente na geometria, mas sofrem de limitações como auto-interseções e maiores requisitos de armazenamento. A intervenção manual de artistas na criação de mapas de rugas e mapas de tensão permite controle, mas pode ser limitada em deformações complexas ou onde maior realismo seja necessário. O nosso trabalho destaca o potencial dos métodos procedimentais para aprimorar a geração de padrões de deformação dinâmica, incluindo rugas, com maior controle criativo e sem depender de dados capturados. A incorporação de padrões procedimentais estáticos melhora o realismo, e a abordagem pode ser estendida além da pele para outros materiais macios.We propose a solution for generating dynamic heightmap data to simulate deformations for soft surfaces, with a focus on human skin. The solution incorporates mesostructure-level wrinkles and utilizes procedural textures to add static microstructure details. It offers flexibility beyond human skin, enabling the generation of patterns mimicking deformations in other soft materials, such as leater, during animation. Existing solutions for simulating wrinkles and deformation cues often rely on specialized hardware, which is costly and not easily accessible. Moreover, relying solely on captured data limits artistic direction and hinders adaptability to changes. In contrast, our proposed solution provides dynamic texture synthesis that adapts to underlying mesh deformations. Various methods have been explored to synthesize wrinkles directly to the geometry, but they suffer from limitations such as self-intersections and increased storage requirements. Manual intervention by artists using wrinkle maps and tension maps provides control but may be limited to the physics-based simulations. Our research presents the potential of procedural methods to enhance the generation of dynamic deformation patterns, including wrinkles, with greater creative control and without reliance on captured data. Incorporating static procedural patterns improves realism, and the approach can be extended to other soft-materials beyond skin
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