Contrôle artistique par édition de la propagation des rayons en photon mapping

National audiencePhysically based rendering with global illumination effects, has become a standard technique for high quality computer generated imagery. Nonetheless, being able to control the resulting picture so that it corresponds to the artist vision is still a tedious trial and error process. We introduce a path selection and edition metaphor, to give the artist a precise control over the final rendering without modifying the scene parameters. Starting from the identification of a lighting feature and its transcription in a path space regular expression, the proposed approach consists in selecting the corresponding light transport paths in 3D space and transforms them according to user defined operations.These operations affect both the geometry and the color spectrum of the paths.We demonstrate the wide range of control it permits on various lighting features, from low frequency color bleeding to high frequency caustics as well as view-dependent reflections.e rendu produisant des effets d'éclairement global est devenu un standard pour la synthèse d'image de haute qualité.Néanmoins, les graphistes ne peuvent éditer les images générées informatiquement qu'au prix d'un travail long et fastidieux sur la définition des sources de lumières et des matériaux de la scène 3D.Nous proposons une approche d'édition qui donne un contrôle précis sur le rendu final, sans modifier les paramètres de la scène 3D.À partir de l'identification d'un effet lumineux définie par une syntaxe d'interaction, l'approche consiste à sélectionner des chemins de transport lumineux et de les transformer suivant des opérations définies par le graphiste.Ces opérations sont des transformations sur la géométrie du transport lumineux ainsi que sur les spectres transportés par les chemins.Nous montrons la large gamme d'éditions que notre approche permet sur divers effets lumineux, allant des variations basses fréquences de diffusion indirecte de couleur, jusqu'aux variations hautes fréquences typiques des caustiques

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

Toward Evaluating Lighting Design Interface Paradigms for Novice Users

Lighting design is a complex and fundamental task in computer cinematography, involving adjustment of light parameters to define final scene appearance. Many lighting interfaces have been proposed to improve lighting design work flow. These paradigms exist in three paradigm categories: direct light parameter manipulation, indirect light feature manipulation (e.g., shadow dragging), and goal-based optimization of light through painting. To this date, no formal evaluation of the relative effectiveness of these methods has been performed. In this paper, we present a first step toward evaluating the three paradigms in the form of a user study with novice users. We focus our evaluation on simple tasks that directly affect lighting features, such as highlights, shadows and intensity gradients, in scenes with up to 2 point lights and 5 objects under direct illumination. We perform quantitative experiments to measure relative efficiency between interfaces together with qualitative input to explore the intuitiveness of the paradigms. Our results indicate that paint-based goal specification is more cumbersome than either direct or indirect manipulation. Furthermore, our investigation suggests improvements to not only the implementation of the paradigms, but also overall paradigm structure for further exploration

Computational rim illumination of dynamic subjects using aerial robots

Lighting plays a major role in photography. Professional photographers use elaborate installations to light their subjects and achieve sophisticated styles. However, lighting moving subjects performing dynamic tasks presents significant challenges and requires expensive manual intervention. A skilled additional assistant might be needed to reposition lights as the subject changes pose or moves, and the extra logistics significantly raises costs and time. The associated latencies as the assistant lights the subject, and the communication required from the photographer to achieve optimum lighting could mean missing a critical shot. We present a new approach to lighting dynamic subjects where an aerial robot equipped with a portable light source lights the subject to automatically achieve a desired lighting effect. We focus on rim lighting, a particularly challenging effect to achieve with dynamic subjects, and allow the photographer to specify a required rim width. Our algorithm processes the images from the photographer׳s camera and provides necessary motion commands to the aerial robot to achieve the desired rim width in the resulting photographs. With an indoor setup, we demonstrate a control approach that localizes the aerial robot with reference to the subject and tracks the subject to achieve the necessary motion. In addition to indoor experiments, we perform open-loop outdoor experiments in a realistic photo-shooting scenario to understand lighting ergonomics. Our proof-of-concept results demonstrate the utility of robots in computational lighting

A study of the need for improvement in classroom environment for optimum pupil growth, development and performance as an integrated whole

The need for visual-centered classrooms

The Prophet and the Pendulum: Sensational Science and Audiovisual Phantasmagoria Around 1848

During the French Second Republic—the volatile period between the 1848 Revolution and Louis-Napoléon Bonaparte’s 1851 coup d’état—two striking performances fired the imaginations of Parisian audiences. The first, in 1849, was a return: after more than a decade, the master of the Parisian grand opera, Giacomo Meyerbeer, launched Le prophète, whose complex instrumentation and astounding visuals—including the unprecedented use of electric lighting—surpassed even his own previous innovations in sound and vision. The second, in 1851, was a debut: the installation of Foucault’s pendulum in the Panthéon. The installation marked the first public exposure of one of the most celebrated demonstrations in the history of science. A heavy copper ball suspended from the former cathedral’s copula, once set in motion, swung in a plane that slowly traced a circle on the marble floor, demonstrating the rotation of the earth

LightGuider: Guiding Interactive Lighting Design using Suggestions, Provenance, and Quality Visualization

LightGuider is a novel guidance-based approach to interactive lighting design, which typically consists of interleaved 3D modeling operations and light transport simulations. Rather than having designers use a trial-and-error approach to match their illumination constraints and aesthetic goals, LightGuider supports the process by simulating potential next modeling steps that can deliver the most significant improvements. LightGuider takes predefined quality criteria and the current focus of the designer into account to visualize suggestions for lighting-design improvements via a specialized provenance tree. This provenance tree integrates snapshot visualizations of how well a design meets the given quality criteria weighted by the designer's preferences. This integration facilitates the analysis of quality improvements over the course of a modeling workflow as well as the comparison of alternative design solutions. We evaluate our approach with three lighting designers to illustrate its usefulness

Washington University Record, September 29, 1994

https://digitalcommons.wustl.edu/record/1664/thumbnail.jp

Efficient global illumination calculation for inverse lighting problems

La luz es un elemento clave en la manera en que percibimos y experimentamos nuestro entorno. Como tal, es un objeto mas a modelar en el proceso de diseño, de forma similar a como ocurre con las formas y los materiales. Las intenciones de iluminacion (LI) son los objetivos y restricciones que el diseñador pretende alcanzar en el proceso del diseño de iluminaci´on: ¿qué superficies se deben iluminar con luz natural y cuales con luz artificial?, ¿qué zonas deben estar en sombra?, ¿cuales son las intensidades maximas y mínimas permitidas? Satisfacer las LI consiste en encontrar la ubicacion, forma e intensidad adecuada de las fuentes luminosas. Este tipo de problemas se define como un problema inverso de iluminacion (ILP) que se resuelve con tecnicas de optimizacion. En el contexto anterior, el objetivo de esta tesis consiste en proponer metodos eficientes para resolver ILP. Este objetivo es motivado por la brecha percibida entre los problemas habituales de diseño de iluminacion y las herramientas computacionales existentes para su resolucion. Las herramientas desarrolladas por la industria se especializan en evaluar configuraciones de iluminacion previamente diseñadas, y las desarrolladas por la academia resuelven problemas relativamente sencillos a costos elevados. Las propuestas cubren distintos aspectos del proceso de optimizacion, que van desde la formulacion del problema a su resolucion. Estan desarrolladas para el caso en que las superficies poseen reflexion e iluminacion difusas y se basan en el calculo de una aproximacion de rango bajo de la matriz de radiosidad. Algunos resultados obtenidos son: el calculo acelerado de la radiosidad de la escena en una unidad de procesamiento gr´afico (GPU); el uso de la heuristica \201Cvariable neighborhood search\201D (VNS) para la resolucion de ILP; el planteo de una estructura multinivel para tratar ILP de forma escalonada; y el uso de tecnicas para optimizar la configuracion de filtros de luz. Otros resultados obtenidos se basan en la formulacion de las LI en funcion de la media y desviacion estandar de las radiosidades halladas. Se propone un metodo para generar LI que contengan esos parametros estadisticos, y otro metodo para acelerar su evaluacion. Con estos resultados se logran tiempos de respuesta interactivos. Por último, las tecnicas anteriores adolecen de una etapa de pre-cómputo relativamente costosa, por tanto se propone acelerar el calculo de la inversa de la matriz de radiosidad a partir de una muestra de factores de forma. Los métodos aquí presentados fueron publicados en seis articulos, tres de ellos en congresos internacionales y tres en revistas arbitradas.Light is a key element that influences the way we perceive and experience our environment. As such, light is an object to be modeled in the design process, as happens with the forms and materials. The lighting intentions (LI) are the objectives and constraints that designers want to achieve in the process of lighting design: which surfaces should be illuminated with natural and which with artificial light?, which surfaces should be in shadow?, which are the maximum and minimum intensities allowed? The fulfillment of the LI consists in finding the location, shape and intensity appropriate for the light sources. This problem is defined as an inverse lighting problem (ILP), solved by optimization techniques. In the above context, the aim of this thesis is the proposal of efficient methods to solve ILP. This objective is motivated by the perceived gap between the usual problems of lighting design, and the computational tools developed for its resolution. The tools developed by the industry specialize in evaluating previously designed lighting configurations, and those developed by the academia solve relatively simple problems at a high computational cost. The proposals cover several aspects of the optimization process, ranging from the formulation of the problem to its resolution. They are developed for the case in which the surfaces have Lambertian reflection and illumination, and are based on the calculation of a low rank approximation to the radiosity matrix. Some results are: rapid calculation of radiosity of the scene in a graphics processing unit (GPU), the use of heuristics “variable neighborhood search” (VNS) for solving ILP, the proposition of a multilevel structure to solve ILP in a stepwise approach, and the use of these techniques to optimize the configuration of light filters. Other results are based on the formulation of LI that use the mean and standard deviation of the radiosity values found. A method is proposed for generating LI containing these parameters, and another method is developed to speed up their evaluations. With these results we achieve interactive response times. Finally, the above techniques suffer from a costly pre-computing stage and therefore, a method is proposed to accelerate the calculation of the radiosity inverse matrix based on a sample of the form factors. The methods presented here were published in six articles, three of them at international conferences and three in peer reviewed journals

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

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