Separable Subsurface Scattering

In this paper, we propose two real-time models for simulating subsurface scattering for a large variety of translucent materials, which need under 0.5 ms per frame to execute. This makes them a practical option for real-time production scenarios. Current state-of-the-art, real-time approaches simulate subsurface light transport by approximating the radially symmetric non-separable diffusion kernel with a sum of separable Gaussians, which requires multiple (up to 12) 1D convolutions. In this work we relax the requirement of radial symmetry to approximate a 2D diffuse reflectance profile by a single separable kernel. We first show that low-rank approximations based on matrix factorization outperform previous approaches, but they still need several passes to get good results. To solve this, we present two different separable models: the first one yields a high-quality diffusion simulation, while the second one offers an attractive trade-off between physical accuracy and artistic control. Both allow rendering of subsurface scattering using only two 1D convolutions, reducing both execution time and memory consumption, while delivering results comparable to techniques with higher cost. Using our importance-sampling and jittering strategies, only seven samples per pixel are required. Our methods can be implemented as simple post-processing steps without intrusive changes to existing rendering pipelines

Interactive Rendering of Scattering and Refraction Effects in Heterogeneous Media

In this dissertation we investigate the problem of interactive and real-time visualization of single scattering, multiple scattering and refraction effects in heterogeneous volumes. Our proposed solutions span a variety of use scenarios: from a very fast yet physically-based approximation to a physically accurate simulation of microscopic light transmission. We add to the state of the art by introducing a novel precomputation and sampling strategy, a system for efficiently parallelizing the computation of different volumetric effects, and a new and fast version of the Discrete Ordinates Method. Finally, we also present a collateral work on real-time 3D acquisition devices

Fast simulation of translucent objects

The existing literature provides a wide variety of previous work regarding Subsurface Scattering e ects. These include pre-processed algorithms, and real-time techniques. On the next lines some of these techniques will be discussed and analyzed in order to know those that led us to the algorithm that we presen

Physically-based rendering of human skin

This thesis explores a set of screen space physically-based subsurface scattering algorithms in order to improve the rendering of scanned human faces. Moreover, it presents extensions and introduces some PBR strategies to produce high quality renders. Finally, the implemented methods are evaluated

Compression, Modeling, and Real-Time Rendering of Realistic Materials and Objects

The realism of a scene basically depends on the quality of the geometry, the illumination and the materials that are used. Whereas many sources for the creation of three-dimensional geometry exist and numerous algorithms for the approximation of global illumination were presented, the acquisition and rendering of realistic materials remains a challenging problem. Realistic materials are very important in computer graphics, because they describe the reflectance properties of surfaces, which are based on the interaction of light and matter. In the real world, an enormous diversity of materials can be found, comprising very different properties. One important objective in computer graphics is to understand these processes, to formalize them and to finally simulate them. For this purpose various analytical models do already exist, but their parameterization remains difficult as the number of parameters is usually very high. Also, they fail for very complex materials that occur in the real world. Measured materials, on the other hand, are prone to long acquisition time and to huge input data size. Although very efficient statistical compression algorithms were presented, most of them do not allow for editability, such as altering the diffuse color or mesostructure. In this thesis, a material representation is introduced that makes it possible to edit these features. This makes it possible to re-use the acquisition results in order to easily and quickly create deviations of the original material. These deviations may be subtle, but also substantial, allowing for a wide spectrum of material appearances. The approach presented in this thesis is not based on compression, but on a decomposition of the surface into several materials with different reflection properties. Based on a microfacette model, the light-matter interaction is represented by a function that can be stored in an ordinary two-dimensional texture. Additionally, depth information, local rotations, and the diffuse color are stored in these textures. As a result of the decomposition, some of the original information is inevitably lost, therefore an algorithm for the efficient simulation of subsurface scattering is presented as well. Another contribution of this work is a novel perception-based simplification metric that includes the material of an object. This metric comprises features of the human visual system, for example trichromatic color perception or reduced resolution. The proposed metric allows for a more aggressive simplification in regions where geometric metrics do not simplif

New acquisition techniques for real objects and light sources in computer graphics

Accurate representations of objects and light sources in a scene model are a crucial prerequisite for realistic image synthesis using computer graphics techniques. This thesis presents techniques for the effcient acquisition of real world objects and real world light sources, as well as an assessment of the quality of the acquired models. Making use of color management techniques, we setup an appearance reproduction pipeline that ensures best-possible reproduction of local light reflection with the available input and output devices. We introduce a hierarchical model for the subsurface light transport in translucent objects, derive an acquisition methodology, and acquire models of several translucent objects that can be rendered interactively. Since geometry models of real world objects are often acquired using 3D range scanners, we also present a method based on the concept of modulation transfer functions to evaluate their accuracy. In order to illuminate a scene with realistic light sources, we propose a method to acquire a model of the near-field emission pattern of a light source with optical prefiltering. We apply this method to several light sources with different emission characteristics and demonstrate the integration of the acquired models into both, global illumination as well as hardware-accelerated rendering systems.Exakte Repräsentationen der Objekte und Lichtquellen in einem Modell einer Szene sind eine unerlässliche Voraussetzung für die realistische Bilderzeugung mit Techniken der Computergraphik. Diese Dissertation beschäftigt sich mit der effizienten Digitalisierung von realen Objekten und realen Lichtquellen. Dabei werden sowohl neue Digitalisierungstechniken als auch Methoden zur Bestimmung der Qualität der erzeugten Modelle vorgestellt. Wir schlagen eine Verarbeitungskette zur Digitalisierung und Wiedergabe der Farbe und Spekularität von Objekten vor, die durch Ausnutzung von Farbmanagementtechniken eine bestmögliche Wiedergabe des Objekts unter Verwendung der gegebenen Ein- und Ausgabegeräte ermöglicht. Wir führen weiterhin ein hierarchisches Modell für den Lichttransport im Inneren von Objekten aus durchscheinenden Materialien sowie eine zugehörige Akquisitionsmethode ein und digitalisieren mehrere reale Objekte. Die dabei erzeugten Modelle können in Echtzeit angezeigt werden. Die Geometrie realer Objekte spielt eine entscheidende Rolle in vielen Anwendungen und wird oftmals unter Verwendung von 3D Scannern digitalisiert. Wir entwickeln daher eine Methode zur Bestimmung der Genauigkeit eines 3D Scanners, die auf dem Konzept der Modulationstransferfunktion basiert. Um eine Szene mit realen Lichtquellen beleuchten zu können, schlagen wir ferner eine Methode zur Erfassung der Nahfeldabstrahlung eine Lichtquelle vor, bei der vor der Digitalisierung ein optischer Filterungsschritt durchgeführt wird. Wir wenden diese Methode zur Digitalisierung mehrerer Lichtquellen mit unterschiedlichen Abstrahlcharakteristika an und zeigen auf, wie die dabei erzeugten Modelle in globalen Beleuchtungsberechnungen sowie bei der Bildsynthese mittels moderner Graphikkarten verwendet werden können

Rendering Deformable Surface Reflectance Fields

Animation of photorealistic computer graphics models is an important goal for many applications. Image-based modeling has emerged as a promising approach to capture and visualize real-world objects. Animating image-based models, however, is still a largely unsolved problem. In this paper, we extend a popular image-based representation called surface reflectance field to animate and render deformable real-world objects under arbitrary illumination. Deforming the surface reflectance field is achieved by modifying the underlying impostor geometry. We augment the impostor by a local parameterization that allows the correct evaluation of acquired reflectance images, preserving the original light model on the deformed surface. We present a deferred shading scheme to handle the increased amount of data involved in shading the deformable surface reflectance field. We show animations of various objects that were acquired with 3D photography.Engineering and Applied Science