11 research outputs found

    Analyse de l'espace des chemins pour la composition des ombres et lumières

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    La réalisation des films d'animation 3D s'appuie de nos jours sur les techniques de rendu physiquement réaliste, qui simulent la propagation de la lumière dans chaque scène. Dans ce contexte, les graphistes 3D doivent jouer avec les effets de lumière pour accompagner la mise en scène, dérouler la narration du film, et transmettre son contenu émotionnel aux spectateurs. Cependant, les équations qui modélisent le comportement de la lumière laissent peu de place à l'expression artistique. De plus, l'édition de l'éclairage par essai-erreur est ralentie par les longs temps de rendu associés aux méthodes physiquement réalistes, ce qui rend fastidieux le travail des graphistes. Pour pallier ce problème, les studios d'animation ont souvent recours à la composition, où les graphistes retravaillent l'image en associant plusieurs calques issus du processus de rendu. Ces calques peuvent contenir des informations géométriques sur la scène, ou bien isoler un effet lumineux intéressant. L'avantage de la composition est de permettre une interaction en temps réel, basée sur les méthodes classiques d'édition en espace image. Notre contribution principale est la définition d'un nouveau type de calque pour la composition, le calque d'ombre. Un calque d'ombre contient la quantité d'énergie perdue dans la scène à cause du blocage des rayons lumineux par un objet choisi. Comparée aux outils existants, notre approche présente plusieurs avantages pour l'édition. D'abord, sa signification physique est simple à concevoir : lorsque l'on ajoute le calque d'ombre et l'image originale, toute ombre due à l'objet choisi disparaît. En comparaison, un masque d'ombre classique représente la fraction de rayons bloqués en chaque pixel, une information en valeurs de gris qui ne peut servir que d'approximation pour guider la composition. Ensuite, le calque d'ombre est compatible avec l'éclairage global : il enregistre l'énergie perdue depuis les sources secondaires, réfléchies au moins une fois dans la scène, là où les méthodes actuelles ne considèrent que les sources primaires. Enfin, nous démontrons l'existence d'une surestimation de l'éclairage dans trois logiciels de rendu différents lorsque le graphiste désactive les ombres pour un objet ; notre définition corrige ce défaut. Nous présentons un prototype d'implémentation des calques d'ombres à partir de quelques modifications du Path Tracing, l'algorithme de choix en production. Il exporte l'image originale et un nombre arbitraire de calques d'ombres liés à différents objets en une passe de rendu, requérant un temps supplémentaire de l'ordre de 15% dans des scènes à géométrie complexe et contenant plusieurs milieux participants. Des paramètres optionnels sont aussi proposés au graphiste pour affiner le rendu des calques d'ombres.The production of 3D animated motion picture now relies on physically realistic rendering techniques, that simulate light propagation within each scene. In this context, 3D artists must leverage lighting effects to support staging, deploy the film's narrative, and convey its emotional content to viewers. However, the equations that model the behavior of light leave little room for artistic expression. In addition, editing illumination by trial-and-error is tedious due to the long render times that physically realistic rendering requires. To remedy these problems, most animation studios resort to compositing, where artists rework a frame by associating multiple layers exported during rendering. These layers can contain geometric information on the scene, or isolate a particular lighting effect. The advantage of compositing is that interactions take place in real time, and are based on conventional image space operations. Our main contribution is the definition of a new type of layer for compositing, the shadow layer. A shadow layer contains the amount of energy lost in the scene due to the occlusion of light rays by a given object. Compared to existing tools, our approach presents several advantages for artistic editing. First, its physical meaning is straightforward: when a shadow layer is added to the original image, any shadow created by the chosen object disappears. In comparison, a traditional shadow matte represents the ratio of occluded rays at a pixel, a grayscale information that can only serve as an approximation to guide compositing operations. Second, shadow layers are compatible with global illumination: they pick up energy lost from secondary light sources that are scattered at least once in the scene, whereas the current methods only consider primary sources. Finally, we prove the existence of an overestimation of illumination in three different renderers when an artist disables the shadow of an object; our definition fixes this shortcoming. We present a prototype implementation for shadow layers obtained from a few modifications of path tracing, the main rendering algorithm in production. It exports the original image and any number of shadow layers associated with different objects in a single rendering pass, with an additional 15% time in scenes containing complex geometry and multiple participating media. Optional parameters are also proposed to the artist to fine-tune the rendering of shadow layers

    Geometry-based shading for shape depiction Enhancement,

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    Recent works on Non-Photorealistic Rendering (NPR) show that object shape enhancement requires sophisticated effects such as: surface details detection and stylized shading. To date, some rendering techniques have been proposed to overcome this issue, but most of which are limited to correlate shape enhancement functionalities to surface feature variations. Therefore, this problem still persists especially in NPR. This paper is an attempt to address this problem by presenting a new approach for enhancing shape depiction of 3D objects in NPR. We first introduce a tweakable shape descriptor that offers versatile func- tionalities for describing the salient features of 3D objects. Then to enhance the classical shading models, we propose a new technique called Geometry-based Shading. This tech- nique controls reflected lighting intensities based on local geometry. Our approach works without any constraint on the choice of material or illumination. We demonstrate results obtained with Blinn-Phong shading, Gooch shading, and cartoon shading. These results prove that our approach produces more satisfying results compared with the results of pre- vious shape depiction techniques. Finally, our approach runs on modern graphics hardware in real time, which works efficiently with interactive 3D visualization

    A workflow for designing stylized shading effects

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    In this report, we describe a workflow for designing stylized shading effects on a 3D object, targeted at technical artists. Shading design, the process of making the illumination of an object in a 3D scene match an artist vision, is usually a time-consuming task because of the complex interactions between materials, geometry, and lighting environment. Physically based methods tend to provide an intuitive and coherent workflow for artists, but they are of limited use in the context of non-photorealistic shading styles. On the other hand, existing stylized shading techniques are either too specialized or require considerable hand-tuning of unintuitive parameters to give a satisfactory result. Our contribution is to separate the design process of individual shading effects in three independent stages: control of its global behavior on the object, addition of procedural details, and colorization. Inspired by the formulation of existing shading models, we expose different shading behaviors to the artist through parametrizations, which have a meaningful visual interpretation. Multiple shading effects can then be composited to obtain complex dynamic appearances. The proposed workflow is fully interactive, with real-time feedback, and allows the intuitive exploration of stylized shading effects, while keeping coherence under varying viewpoints and light configurations. Furthermore, our method makes use of the deferred shading technique, making it easily integrable in existing rendering pipelines.Dans ce rapport, nous décrivons un outil de création de modèles d'illumination adapté à la stylisation de scènes 3D. Contrairement aux modèles d'illumination photoréalistes, qui suivent des contraintes physiques, les modèles d'illumination stylisés répondent à des contraintes artistiques, souvent inspirées de la représentation de la lumière en illustration. Pour cela, la conception de ces modèles stylisés est souvent complexe et coûteuse en temps. De plus, ils doivent produire un résultat cohérent sous une multitude d'angles de vue et d'éclairages. Nous proposons une méthode qui facilite la création d'effets d'illumination stylisés, en décomposant le processus en trois parties indépendantes: contrôle du comportement global de l'illumination, ajout de détails procéduraux, et colorisation.Différents comportements d'illumination sont accessibles à travers des paramétrisations, qui ont une interprétation visuelle, et qui peuvent être combinées pour obtenir des apparences plus complexes. La méthode proposée est interactive, et permet l'exploration efficace de modèles d'illumination stylisés. La méthode est implémentée avec la technique de deferred shading, ce qui la rend facilement utilisable dans des pipelines de rendu existants

    Mock-3D Web Application: Interactive Lighting, Rendering and Shading for 2D Artwork

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    In this thesis, we developed a web-based tool to allow artists to create 3D-looking stylized depictions based on 2D artwork with complete visual control. The controls include multiple lights with diffuse reflections and specular highlights, and refraction and mirror reflection with Fresnel control. Our controls do not necessarily correspond to underlying physical phenomena; however, they still provided results that are visually similar to 3D realistic rendering. The core of this approach is using paintable shape maps, which are similar to normal maps. The shape maps do not have to correspond to 3D shapes and, therefore, they can allow the artist to obtain incoherent and impossible 2D shapes with 3D appearance. Another contribution is that we linearized Fresnel Curve so that it can be controlled by two sliders. This allows it to achieve an intuitive blending of the results of refraction and reflection

    Qualitative Global Illumination of Mock-3D Scenes

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    In this work, we developed a framework to obtain qualitatively acceptable global rendering effects without an explicit geometry. This framework is particularly useful for 2D artists such as painters and illustrators. They will be able to obtain 3D looking images with complete artistic control as if they are using a 2D digital image manipulation system. The core of this approach is a mock-3D scene representation that allows impossible or stylized shapes as “fuzzy” geometric structures. These fuzzy geometric structures are view dependent shapes that are computed from texture maps which provide normal, thickness and displacement information for all visible points of a shape. The information that is provided by these texture maps, which we call shape maps, do not have to be complete or consistent. Shape maps can be obtaining by (1) converting 3D shapes into 2D images, (2) modeling using a sketch based interface, (3) directly painting a gradient domain image or (4) photographing real objects. The most interesting shape maps are those sketched or painted by an artist, since they can reflect the artist’s intention, even if this does not follow the normal rules of perspective. The major advantage of this approach is the ability to obtain visually acceptable global effects even when shape maps do not correspond to real 3D shapes. We show that computing view dependent fuzzy geometry from shape maps is sufficient to obtain qualitatively convincing global illumination effects even for impossible shapes. The methods we have developed and implemented for global rendering effects include ambient occlusion, local and global shadows, refraction and reflection. Although these methods do not directly correspond to underlying physical phenomena, they ii can provide results that are qualitative proportional to 3D realistic rendering. Our approach is a very 2D artist-friendly representation since the shaders are also defined as images. These images can naturally describe shading parameters and provide a simple 2D control of the shading and rendering processes to intuitively obtain desired visual results. In particular, this representational power helps to easily obtain a wide variety of NPR effects that is still consistent with global illumination

    Interactive non-photorealistic rendering

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    Due to increasing demands of artistic style with Interactive Rate, we propose this review paper as a starting point for any person interested in researching of interactive non-photorealistic rendering. As a simple yet effective means of visual communication, interactive non-photorealistic rendering generates images that are closer to human-drawn than are created by traditional computer graphics techniques with more expressing meaningful visual information. This paper presents taxonomy of interactive non-photorealistic rendering techniques which developed over the past two decades, structured according to the design characteristics and behavior of each technique. Also, it covers the most important algorithms in interactive stylized shade and line drawing, and separately discussing their advantages and disadvantages. The review then concludes with a discussion of the main issues and technical challenges for Interactive Non-Photorealistic Rendering techniques. In addition, this paper discusses the effect of modified phong shading model in order to create toon shading appearance

    Bidirectional Appearance Distribution Function for Stylized Shading

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    We define a new shading tool called a Bidirectional Appearance Distribution Function (BADF) tailored to the direct control of stylized appearance. A BADF can be thought of as defining the appearance of a sphere from all possible illumination directions. Our BADF formulation generalizes and improves upon previous stylized shading techniques by enabling the direct control of shading profiles in screen space, exaggerating surface features in a flexible manner, and letting users control stylized appearance from multiple lighting or viewing directions. This allows users to start from a simple shading behavior, and refine from there towards greater stylization. Our GPU implementation works in real-time, which benefits both editing, and rendering in interactive systems. These features make BADFs an efficient tool for many applications in artistic and scientific illustration domains

    Computer-assisted animation creation techniques for hair animation and shade, highlight, and shadow

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    制度:新 ; 報告番号:甲3062号 ; 学位の種類:博士(工学) ; 授与年月日:2010/2/25 ; 早大学位記番号:新532
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