Understanding and controlling contrast oscillations in stochastic texture algorithms using Spectrum of Variance

We identify and analyze a major issue pertaining to all power-spectrum based texture synthesis algorithms – from Fourier synthesis to procedural noise algorithms like Perlin or Gabor noise – , namely, the oscillation of contrast (see Figures 1,2,3,7). One of our key contributions is to introduce a simple yet powerful descriptor of signals, the Spectrum of Variance (not to be confused with the PSD), which, to our surprise, has never been leveraged before. In this new framework, several issues get easy to understand measure and control, with new handles, as we illustrate. We finally show that fixing oscillation of contrast opens many doors to a more controllable authoring of stochastic texturing. We explore some of the new reachable possibilities such as constrained noise content and bridges towards very different families of look such as cellular patterns, points-like distributions or reaction-diffusion

Synthesizing Verdant Landscapes using Volumetric Textures

Projet SYNTIMVolumetric textures are able to represent complex repetitive data such as foliage, fur and forests by storing one sample of geometry in a volumetric {\em texel} to be mapped onto a surface. This volume consists in samples of densities and reflectances stored in voxels. The texel can be prefiltered similarly to the mip-mapping algorithm, giving an efficient rendering in ray-tracing with low aliasing, using a single ray per pixel. Our general purpose is to extend the volumetric texture method in order to provide a convenient and efficient tool for modeling, animating and rendering highly complex scenes in ray-tracing. We illustrate our method with verdant landscapes such as forests and lawns. In our previous work, we have dealt with the multiscale volume representation and texel animation. In this paper, we show how to convert usual 3D models into texels, and how to render texels mapped onto any mesh type. Solving these two issues makes the method usable for a designer

Effets spéciaux

Tangente: Magazine de vulgarisation des mathématiques . http://tangente-mag.com/ISSN 0987-0806La synthèse d’images (parfois appelée « la 3D ») permet de créer dans l’ordinateur des mondes fictifs, ultra-réalistes ou de style cartoon selon l’envie des graphistes, des réalisateurs, des artistes… Mais comment fait-on pour créer un monde ? Avec des mathématiques

A General and Multiscale Model for Volumetric Textures

International audienceThis paper presents an important extension of the volumetric textures introduced by Kajiya in 1989. Volumetric textures are used to model complex geometries (such as foliage, fur, ...) on a textural way, by mapping a 'thick skin' made of a repetitive pattern (the texel) covering a simple surface. Like for the Kajiya's implementation, our model code the reference volume with voxels, which contain in addition to the density an illumination model. (Even if we are far from a waved iron-sheet, it don't look like a flat sheet: shapes can be approximated, but reflectance behavior are different.) The extension lais in a quite generic illumination coding, and more, in the ability of the model to be 'smoothed', so that the representation is similar to the mip-map 2D-textures coding. Thus, it is now possible to compute quite quickly and with low aliasing very complicated scene, the details being represented adaptatively.Cet article présente une extension importante des textures volumiques introduites par Kajiya en 1989. Les textures volumiques permettent de modéliser les géométries complexes (feuillage, fourrure...) à la manière d'une texture, comme une 'peau épaisse' constituée d'un motif répétitif volumique, le texel, recouvrant une surface simple. Comme dans l'implémentation de Kajiya, le modèle proposé code un volume de référence par des voxels, dans lesquel on stocke en plus de la densité un modèle d'illumination. (En effet, même à grande distance, une tôle ondulée n'est pas assimilable à une plaque: si on peu approximer la forme, le comportement en réflectance reste différent.) L'extension réside dans le fait d'utiliser un modèle relativement générique de codage de l'illumination, et surtout dans la capacité du modèle à être 'filtré', de telle sorte que la représentation obtenue soit l'équivalent volumique du codage mip-map des textures 2D. Ainsi, il devient possible de calculer relativement rapidement et avec assez peu d'aliasing des scènes très chargées en détails, la représentation de ceux-ci se faisant de manière adaptative

Local Illumination in Deformed Space

Projet SYNTIMThere are two ways of ray-tracing space-deformed objects: computing the resulting object and rendering it, or directly rendering the object in its initial space by curving rays. This last approach is advantageous for all non-explicit representations that often should otherwise be facetized (CSG, implicit functions), or for large databases for which too many components should be transformed (particle systems, volumes, complex geometry). We deal here with ray casting in a structured space (voxels, complex geometry in volumetric textures, geometry in grids), focusing on the local illumination evaluation, especially in the anisotropic case. We apply it to the ellipsoidal reflectance model developed for volumetric textures in \cite{neyret95}

Un Modèle Général et Multiéchelle de Textures Volumiques

National audienc

S'approprier les maths-physique par la simulation: autour des expérimentations (et logiciel libre) MobiNet

revue en ligne : http://educmath.inrp.fr/Educmath/la-parole-a/f-neyret/editoNational audiencePresentation of the large-scope and thin-scope pedagogic motivations of our MobiNet educational platform, and quick presentation of our experiments in and out the class

Le mouvement sous toutes ses coutures

Maths Mouvement Express: Brochure de vulgarisation mathématique éditée annuellement par le CIJM à l'occasion du Salon Culture & Jeux Mathématiqueshttps://www.cijm.org/accueil/productions-cijm/90-maths-expressQu'est-ce que le "mouvement de l'eau" ? Comment appréhender le mouvement ? Comme bien des questions scientifiques, celle-ci est en fait ambiguë, et il faut d'abord définir précisément de quoi l'on parle, ce qui amènera des réponses très différentes, puis à un tour des nombreuses facettes sous lesquelles les scientifiques et ingénieurs peuvent regarder un champ de mouvement donné

Trimmed Textures

Projet SYNTIMTextures play an important role in the design of synthetic scenes. However, setting textures boundaries independently of the surface mesh edges is still a problem. In this paper, we propose a simple and cheap solution to deal with this problem without modifying the mesh, which introduces an extra cost only for facets containing a texture boundary (by {\em facet}, we mean any kind of surface element (polygon, bicubic patch...), having any kind of parameterisation (barycentric, etc...)). This is achieved by associating to the surface 2D closed curves defining the boundaries of the textures. A pre-processing is done before rendering, clipping and storing these 2D texture trimming curves in each facet, and associating each possible texture to a combination of the areas defined by the curves. At rendering time, the current point is checked relatively to these areas, thus determinating the texture to use on this location of the surface

Synthesizing Verdant Landscape Using Volumetric Textures

International audienceIn this paper, we turn the representation into a real tool: we have dealt with animation in EWAS'95, we deal here with texel construction, mapping, color, etc. We apply these methods to synthesize complex natural scenes.Dans cet article, on s'attache à transformer la représentation en véritable outil: on avait déjà décrit l'animation dans EWAS'95, on traite ici de la construction des texels, de leur mapping, du traitement de la couleur, etc. On applique ces méthodes à la synthèse de scènes naturelles complexes