A Frequency Analysis and Dual Hierarchy for Efficient Rendering of Subsurface Scattering

International audienceBSSRDFs are commonly used to model subsurface light transport in highly scattering media such as skin and marble. Rendering with BSSRDFs requires an additional spatial integration, which can be significantly more expensive than surface-only rendering with BRDFs. We introduce a novel hierarchical rendering method that can mitigate this additional spatial integration cost. Our method has two key components: a novel frequency analysis of subsurface light transport, and a dual hierarchy over shading and illumination samples. Our frequency analysis predicts the spatial and angular variation of outgoing radiance due to a BSSRDF. We use this analysis to drive adaptive spatial BSSRDF integration with sparse image and illumination samples. We propose the use of a dual-tree structure that allows us to simultaneously traverse a tree of shade points (i.e., pixels) and a tree of object-space illumination samples. Our dual-tree approach generalizes existing single-tree accelerations. Both our frequency analysis and the dual-tree structure are compatible with most existing BSSRDF models, and we show that our method improves rendering times compared to the state of the art method of Jensen and Buhler

Real-time rendering of cities at night

En synthèse d’images, déterminer la couleur d’une surface au pixel d’une image doit considérer toutes les sources de lumière de la scène pour évaluer leur contribution lumineuse sur la surface en question. Cette évaluation de la visibilité et en l’occurrence de la radiance incidente des sources de lumière est très coûteuse. Elle n’est généralement pas traitée pour chaque source de lumière en rendu temps-réel. Une ville en pleine nuit est un exemple de telle scène comportant une grande quantité de sources de lumière pour lesquelles les rendus temps-réel modernes ne peuvent pas évaluer la visibilité de toutes les sources de lumière individuelles. Nous présentons une technique exploitant la cohérence spatiale des villes et la co-hérence temporelle des rendus temps-réel pour accélérer le calcul de la visibilité des sources de lumière. Notre technique de visibilité profite des bloqueurs naturels et pré-dominants de la ville pour rapidement réduire la liste de sources de lumière à évaluer etainsi, accélérer le calcul de la visibilité en assumant des bloqueurs sous forme de boîtes alignées majoritairement selon certains axes dominants. Pour garantir la propagation des occultations, nous fusionnons les bloqueurs adjacents dans un seul et même bloqueur conservateur en termes d’occultations. Notre technique relie la visibilité de la caméra avec la visibilité des surfaces pour réduire le nombre d’évaluations à effectuer à chaque rendu, et ne calcule la visibilité que pour les surfaces visibles du point de vue de la caméra. Finalement, nous intégrons la technique de visibilité avec une technique de rendu réaliste, Lightcuts, qui a été mise à jour sur GPU dans un scénario de rendu temps-réel. Même si notre technique ne permettra pas d’atteindre le temps-réel en général dans une scène complexe, elle réduit suffisamment les contraintes pour espérer y arriver un jour.In image synthesis, to determine the final color of a surface at a specific image pixel,we must consider all potential light sources and evaluate if they contribute to the illumination. Since such evaluation is slow, real-time renderers traditionally do not evaluate each light source, and instead preemptively choose locally important light sources for which to evaluate visibility. A city at night is such a scene containing many light sources for which modern real-time renderers cannot allow themselves to evaluate every light source at every frame.We present a technique exploiting spatial coherency in cities and temporal coherency of real-time walkthroughs to reduce visibility evaluations in such scenes. Our technique uses the natural and predominant occluders of a city to efficiently reduce the number of light sources to evaluate. To further accelerate the evaluation we project the bounding boxes of buildings instead of their detailed model (these boxes should be oriented mostly along a few directions), and fuse adjacent occluders on an occlusion plane to form larger conservative occluders. Our technique also integrates results from camera visibility to further reduce the number of visibility evaluations executed per frame, and evaluates visible light sources for facades visible from the point of view of the camera. Finally, we integrate an offline rendering technique, Lightcuts, by adapting it to real-time GPU rendering to further save on rendering time.Even though our technique does not achieve real-time frame rates in a complex scene,it reduces the complexity of the problem enough so that we can hope to achieve such frame rates one day

IlluminationCut

International audienceWe present a novel algorithm, IlluminationCut, for rendering images in the many-lights framework. It handles any light source that can be approximated via VPLs and highly glossy materials. The method effectively creates an illumination aware clustering of the product space of the set of pixels, and the set of VPLs. Our framework is flexible and achieves around 3 − 6 times speedup over previous state-of-the-art algorithms

IlluminationCut

International audienceWe present a novel algorithm, IlluminationCut, for rendering images using the many-lights framework. It handles any light source that can be approximated with virtual point lights (VPLs) as well as highly glossy materials. The algorithm extends the Multidimensional Lightcuts technique by effectively creating an illumination aware clustering of the product-space of the set of points to be shaded and the set of VPLs. Our framework is flexible and achieves around $3-6$ times speedup over previous state-of-the-art methods