Efficient acquisition, representation and rendering of light fields

In this thesis we discuss the representation of three-dimensional scenes using image data (image-based rendering), and more precisely the so-called light field approach. We start with an up-to-date survey on previous work in this young field of research. Then we propose a light field representation based on image data and additional per-pixel depth values. This enables us to reconstruct arbitrary views of the scene in an efficient way and with high quality. Furtermore, we can use the same representation to determine optimal reference views during the acquisition of a light field. We further present the so-called free form parameterization, which allows for a relatively free placement of reference views. Finally, we demonstrate a prototype of the Lumi-Shelf system, which acquires, transmits, and renders the light field of a dynamic scene at multiple frames per second.Diese Doktorarbeit beschäftigt sich mit der Repräsentierung dreidimensionaler Szenen durch Bilddaten (engl. image-based rendering, deutsch bildbasierte Bildsynthese), speziell mit dem Ansatz des sog. Lichtfelds. Nach einem aktuellen Überblick über bisherige Arbeiten in diesem jungen Forschungsgebiet stellen wir eine Datenrepräsentation vor, die auf Bilddaten mit zusätzlichen Tiefenwerten basiert. Damit sind wir in der Lage, beliebige Ansichten der Szene effizient und in hoher Qualität zu rekonstruieren sowie die optimalen Referenz-Ansichten bei der Akquisition eines Lichtfelds zu bestimmen. Weiterhin präsentieren wir die sog. Freiform-Parametrisierung, die eine relativ freie Anordnung der Referenz-Ansichten erlaubt. Abschließend demonstrieren wir einen Prototyp des Lumishelf-Systems, welches die Aufnahme, Übertragung und Darstellung des Lichtfeldes einer dynamischen Szene mit mehreren Bildern pro Sekunde ermöglicht

Efficient acquisition, representation and rendering of light fields

In this thesis we discuss the representation of three-dimensional scenes using image data (image-based rendering), and more precisely the so-called light field approach. We start with an up-to-date survey on previous work in this young field of research. Then we propose a light field representation based on image data and additional per-pixel depth values. This enables us to reconstruct arbitrary views of the scene in an efficient way and with high quality. Furtermore, we can use the same representation to determine optimal reference views during the acquisition of a light field. We further present the so-called free form parameterization, which allows for a relatively free placement of reference views. Finally, we demonstrate a prototype of the Lumi-Shelf system, which acquires, transmits, and renders the light field of a dynamic scene at multiple frames per second.Diese Doktorarbeit beschäftigt sich mit der Repräsentierung dreidimensionaler Szenen durch Bilddaten (engl. image-based rendering, deutsch bildbasierte Bildsynthese), speziell mit dem Ansatz des sog. Lichtfelds. Nach einem aktuellen Überblick über bisherige Arbeiten in diesem jungen Forschungsgebiet stellen wir eine Datenrepräsentation vor, die auf Bilddaten mit zusätzlichen Tiefenwerten basiert. Damit sind wir in der Lage, beliebige Ansichten der Szene effizient und in hoher Qualität zu rekonstruieren sowie die optimalen Referenz-Ansichten bei der Akquisition eines Lichtfelds zu bestimmen. Weiterhin präsentieren wir die sog. Freiform-Parametrisierung, die eine relativ freie Anordnung der Referenz-Ansichten erlaubt. Abschließend demonstrieren wir einen Prototyp des Lumishelf-Systems, welches die Aufnahme, Übertragung und Darstellung des Lichtfeldes einer dynamischen Szene mit mehreren Bildern pro Sekunde ermöglicht

Flux-Limited Diffusion for Multiple Scattering in Participating Media

For the rendering of multiple scattering effects in participating media, methods based on the diffusion approximation are an extremely efficient alternative to Monte Carlo path tracing. However, in sufficiently transparent regions, classical diffusion approximation suffers from non-physical radiative fluxes which leads to a poor match to correct light transport. In particular, this prevents the application of classical diffusion approximation to heterogeneous media, where opaque material is embedded within transparent regions. To address this limitation, we introduce flux-limited diffusion, a technique from the astrophysics domain. This method provides a better approximation to light transport than classical diffusion approximation, particularly when applied to heterogeneous media, and hence broadens the applicability of diffusion-based techniques. We provide an algorithm for flux-limited diffusion, which is validated using the transport theory for a point light source in an infinite homogeneous medium. We further demonstrate that our implementation of flux-limited diffusion produces more accurate renderings of multiple scattering in various heterogeneous datasets than classical diffusion approximation, by comparing both methods to ground truth renderings obtained via volumetric path tracing.Comment: Accepted in Computer Graphics Foru

k-d Darts: Sampling by k-Dimensional Flat Searches

We formalize the notion of sampling a function using k-d darts. A k-d dart is a set of independent, mutually orthogonal, k-dimensional subspaces called k-d flats. Each dart has d choose k flats, aligned with the coordinate axes for efficiency. We show that k-d darts are useful for exploring a function's properties, such as estimating its integral, or finding an exemplar above a threshold. We describe a recipe for converting an algorithm from point sampling to k-d dart sampling, assuming the function can be evaluated along a k-d flat. We demonstrate that k-d darts are more efficient than point-wise samples in high dimensions, depending on the characteristics of the sampling domain: e.g. the subregion of interest has small volume and evaluating the function along a flat is not too expensive. We present three concrete applications using line darts (1-d darts): relaxed maximal Poisson-disk sampling, high-quality rasterization of depth-of-field blur, and estimation of the probability of failure from a response surface for uncertainty quantification. In these applications, line darts achieve the same fidelity output as point darts in less time. We also demonstrate the accuracy of higher dimensional darts for a volume estimation problem. For Poisson-disk sampling, we use significantly less memory, enabling the generation of larger point clouds in higher dimensions.Comment: 19 pages 16 figure

Path-tracing Monte Carlo Library for 3D Radiative Transfer in Highly Resolved Cloudy Atmospheres

Interactions between clouds and radiation are at the root of many difficulties in numerically predicting future weather and climate and in retrieving the state of the atmosphere from remote sensing observations. The large range of issues related to these interactions, and in particular to three-dimensional interactions, motivated the development of accurate radiative tools able to compute all types of radiative metrics, from monochromatic, local and directional observables, to integrated energetic quantities. In the continuity of this community effort, we propose here an open-source library for general use in Monte Carlo algorithms. This library is devoted to the acceleration of path-tracing in complex data, typically high-resolution large-domain grounds and clouds. The main algorithmic advances embedded in the library are those related to the construction and traversal of hierarchical grids accelerating the tracing of paths through heterogeneous fields in null-collision (maximum cross-section) algorithms. We show that with these hierarchical grids, the computing time is only weakly sensitivive to the refinement of the volumetric data. The library is tested with a rendering algorithm that produces synthetic images of cloud radiances. Two other examples are given as illustrations, that are respectively used to analyse the transmission of solar radiation under a cloud together with its sensitivity to an optical parameter, and to assess a parametrization of 3D radiative effects of clouds.Comment: Submitted to JAMES, revised and submitted again (this is v2