Improving Shape Depiction under Arbitrary Rendering

International audienceBased on the observation that shading conveys shape information through intensity gradients, we present a new technique called Radiance Scaling that modifies the classical shading equations to offer versatile shape depiction functionalities. It works by scaling reflected light intensities depending on both surface curvature and material characteristics. As a result, diffuse shading or highlight variations become correlated to surface feature variations, enhancing concavities and convexities. The first advantage of such an approach is that it produces satisfying results with any kind of material for direct and global illumination: we demonstrate results obtained with Phong and Ashikmin-Shirley BRDFs, Cartoon shading, sub-Lambertian materials, perfectly reflective or refractive objects. Another advantage is that there is no restriction to the choice of lighting environment: it works with a single light, area lights, and inter-reflections. Third, it may be adapted to enhance surface shape through the use of precomputed radiance data such as Ambient Occlusion, Prefiltered Environment Maps or Lit Spheres. Finally, our approach works in real-time on modern graphics hardware making it suitable for any interactive 3D visualization

Transfert de couleurs et colorisation guidés par la texture

National audienceCet article se concentre sur deux problèmes de manipulation de couleurs liés : le transfert de couleurs qui modifie les couleurs d'une image, et la colorisation qui ajoute des couleurs à une image en niveaux de gris. Les méthodes automatiques pour ces deux applications modifient l'image d'entrée à l'aide d'une image de référence contenant les couleurs désirées. Les approches précédentes visent rarement les deux problèmes simultanement et souffrent de deux principales limitations : les correspondances créées entre les images d'entrée et de référence sont incorrectes ou approximatives, et une mauvaise cohérence spatiale autour des structures de l'image. Dans cet article, nous proposons un pipeline unifiant les deux problèmes, basé sur le contenu texturel des images pour guider le transfert ou la colorisation. Notre méthode introduit un descripteur de textures préservant les contours de l'image, basé sur des matrices de covariance, permettant d'appliquer des transformations de couleurs locales. Nous montrons que notre approche est capable de produire des résultats comparables ou meilleurs que d'autres méthodes de l'état de l'art dans les deux applications

A Programmable Model for Designing Stationary 2D Arrangements

This paper introduces a programmable method for designing stationary 2D arrangements for element textures, namely textures made of small geometric elements. These textures are ubiquitous in numerous applications of computer-aided illustration. Previous methods, whether they be example-based or layout-based, lack control and can produce a limited range of possible arrangements. Our approach targets technical artists who will design an arrangement by writing a script.These scripts are using three types of operators: partitioning operators for defining the broad-scale organization of the arrangement, mapping operators for controlling the local organization of elements, and merging operators for mixing different arrangements. These operators are designed so as to guarantee a stationary result meaning that the produced arrangements will always be repetitive. We show that this simple set of operators is sufficient to reach a much broader variety of arrangements than previous methods. Editing the script leads to predictable changes in the synthesized arrangement, which allows an easy iterative design of complex structures. Finally, our operator set is extensible and can be adapted to application-dependent needs

Dynamic Stylized Shading Primitives

Honorable Mention in RenderingInternational audienceShading appearance in illustrations, comics and graphic novels is designed to convey illumination, material and surface shape characteristics at once. Moreover, shading may vary depending on different configurations of surface distance, lighting, character expressions, timing of the action, to articulate storytelling or draw attention to a part of an object. In this paper, we present a method that imitates such expressive stylized shading techniques in dynamic 3D scenes, and which offers a simple and flexible means for artists to design and tweak the shading appearance and its dynamic behavior. The key contribution of our approach is to seamlessly vary appearance by using a combination of shading primitives that take into account lighting direction, material characteristics and surface features. We demonstrate their flexibility in a number of scenarios: minimal shading, comics or cartoon rendering, glossy and anisotropic material effects; including a variety of dynamic variations based on orientation, timing or depth. Our prototype implementation combines shading primitives with a layered approach and runs in real-time on the GPU

Discrete Texture Design Using a Programmable Approach

International audienceIn this work, we call "discrete texture" any repetitive pattern composed of small, perceivable elements. A lot of art techniques involve manual production of discrete textures, that is very expensive. We address the problem of discrete texture synthesis. Previous works introduced by-example tools: simple interfaces that allow one to draw a small texture exemplar. The tool analyses this exemplar and reproduces it on a larger scale. However, these algorithms fail to reproduce faithfully both large scale effects and local structures of elements. In contrast, our approach allows one to write the program that synthesizes the texture. We provide a set of operators that distribute points, curves or regions in the plane. We show that a large range of textures can be easily designed with our system. Additionaly, we prove that many variants of classic element distribution algorithms can be written as simple combinations of our operators

Designing Gratin, A GPU-Tailored Node-Based System

International audienceNodal architectures have received an ever-increasing endorsement in computer graphics in recent years. However, creating a node-based system specifically tailored to GPU-centered applications with real-time performance is not straightforward. In this paper, we discuss the design choices we took in the making of Gratin, our open-source node-based system. This information is useful to graphics experts interested in crafting their own node-based system working on the GPU, either starting from scratch or taking inspiration from our source code. We first detail the architecture of Gratin at the graph level, with data structures permitting real- time updates even for large pipelines. We then present the design choices we made at the node level, which provide for three levels of programmability and, hence, a gentle learning curve. Finally, we show the benefits of our approach by presenting use cases in research prototyping and teaching

Automatic lighting design from photographic rules

International audienceLighting design is crucial in 3D scenes modeling for its ability to provide cues to understand the objects shape. However a lot of time, skills, trials and errors are required to obtain a desired result. Existing automatic lighting methods for conveying the shape of 3D objects are based either on costly optimizations or on non-realistic shading effects. Also they do not take the material information into account. In this paper, we propose a new method that automatically suggests a lighting setup to reveal the shape of a 3D model, taking into account its material and its geometric properties. Our method is independent from the rendering algorithm. It is based on lighting rules extracted from photography books, applied through a fast and simple geometric analysis. We illustrate our algorithm on objects having different shapes and materials, and we show by both visual and metric evaluation that it is comparable to optimization methods in terms of lighting setups quality. Thanks to its genericity our algorithm could be integrated in any rendering pipeline to suggest appropriate lighting

Stylisation d'objets éclairés par des cartes d'environnement HDR

National audienceDans cet article, nous introduisons un pipeline de rendu permettant de styliser de manière interactive des objets éclairés par des cartes d'environnement à grande dynamique (High-Dynamic Range ou HDR). L'utilisation d'images HDR permet d'améliorer la qualité de certains traitements, comme les segmentations ou l'extraction des détails. De plus, cette architecture permet de combiner facilement des stylisations 2D (sur la carte d'environnement et sur les images) et 3D (sur les objets). Les nouveaux styles que nous présentons sont basés sur ce pipeline et illustrent la flexibilité de notre approche

Utilisation du rendu expressif pour l'illustration et l'exploration de données archéologiques

National audienceLe rendu expressif est une branche relativement jeune de la synthèse d'images qui s'intéresse non pas à créer des images qui sont le résultat de simulations de phénomènes physiques réalistes, mais qui tend à communiquer visuellement des informations sur les objets représentés par le biais de styles variés (dessin, aquarelle, etc). Ce type de rendu semble particulièrement adapté au domaine de l'archéologie pour deux raisons : il permet d'illustrer les hypothèses de reconstruction 3D archéologiques sans pour autant biaiser l'interprétation par une représentation trop réaliste et peut aussi apporter une méthode visuelle intuitive d'exploration de données archéologiques. Dans cet exposé, nous allons tout d'abord présenter les travaux que nous avons réalisé par le passé portant sur la création d'illustrations (effets de papier, aquarelle). Puis nous allons introduire les aspects du rendu expressif qui permettraient l'exploration sémantique de données archéologiques

Radiance Scaling for Versatile Surface Enhancement

International audienceWe present a novel technique called Radiance Scaling for the depiction of surface shape through shading. It adjusts reflected light intensities in a way dependent on both surface curvature and material characteristics. As a result, diffuse shading or highlight variations become correlated to surface feature variations, enhancing surface concavities and convexities. This approach is more versatile compared to previous methods. First, it produces satisfying results with any kind of material: we demonstrate results obtained with Phong and Ashikmin BRDFs, Cartoon shading, sub-Lambertian materials, and perfectly reflective or refractive objects. Second, it imposes no restriction on lighting environment: it does not require a dense sampling of lighting directions and works even with a single light. Third, it makes it possible to enhance surface shape through the use of precomputed radiance data such as Ambient Occlusion, Prefiltered Environment Maps or Lit Spheres. Our novel approach works in real-time on modern graphics hardware and is faster than previous techniques