Browsing by Author "Bonneel, Nicolas"

Now showing 1 - 4 of 4
  • No Thumbnail Available
    Item
    Mumford-Shah Mesh Processing using the Ambrosio-Tortorelli Functional
    (The Eurographics Association and John Wiley & Sons Ltd., 2018) Bonneel, Nicolas; Coeurjolly, David; Gueth, Pierre; Lachaud, Jacques-Olivier; Fu, Hongbo and Ghosh, Abhijeet and Kopf, Johannes
    The Mumford-Shah functional approximates a function by a piecewise smooth function. Its versatility makes it ideal for tasks such as image segmentation or restoration, and it is now a widespread tool of image processing. Recent work has started to investigate its use for mesh segmentation and feature lines detection, but we take the stance that the power of this functional could reach far beyond these tasks and integrate the everyday mesh processing toolbox. In this paper, we discretize an Ambrosio-Tortorelli approximation via a Discrete Exterior Calculus formulation. We show that, combined with a new shape optimization routine, several mesh processing problems can be readily tackled within the same framework. In particular, we illustrate applications in mesh denoising, normal map embossing, mesh inpainting and mesh segmentation.
  • Thumbnail Image
    Item
    Perceptual Quality of BRDF Approximations: Dataset and Metrics
    (The Eurographics Association and John Wiley & Sons Ltd., 2021) LavouƩ, Guillaume; Bonneel, Nicolas; Farrugia, Jean-Philippe; Soler, Cyril; Mitra, Niloy and Viola, Ivan
    Bidirectional Reflectance Distribution Functions (BRDFs) are pivotal to the perceived realism in image synthesis. While measured BRDF datasets are available, reflectance functions are most of the time approximated by analytical formulas for storage efficiency reasons. These approximations are often obtained by minimizing metrics such as L2-or weighted quadratic- distances, but these metrics do not usually correlate well with perceptual quality when the BRDF is used in a rendering context, which motivates a perceptual study. The contributions of this paper are threefold. First, we perform a large-scale user study to assess the perceptual quality of 2026 BRDF approximations, resulting in 84138 judgments across 1005 unique participants. We explore this dataset and analyze perceptual scores based on material type and illumination. Second, we assess nine analytical BRDF models in their ability to approximate tabulated BRDFs. Third, we assess several image-based and BRDF-based (Lp, optimal transport and kernel distance) metrics in their ability to approximate perceptual similarity judgments.
  • No Thumbnail Available
    Item
    A Survey of Optimal Transport for Computer Graphics and Computer Vision
    (The Eurographics Association and John Wiley & Sons Ltd., 2023) Bonneel, Nicolas; Digne, Julie; Bousseau, Adrien; Theobalt, Christian
    Optimal transport is a long-standing theory that has been studied in depth from both theoretical and numerical point of views. Starting from the 50s this theory has also found a lot of applications in operational research. Over the last 30 years it has spread to computer vision and computer graphics and is now becoming hard to ignore. Still, its mathematical complexity can make it difficult to comprehend, and as such, computer vision and computer graphics researchers may find it hard to follow recent developments in their field related to optimal transport. This survey first briefly introduces the theory of optimal transport in layman's terms as well as most common numerical techniques to solve it. More importantly, it presents applications of these numerical techniques to solve various computer graphics and vision related problems. This involves applications ranging from image processing, geometry processing, rendering, fluid simulation, to computational optics, and many more. It is aimed at computer graphics researchers desiring to follow optimal transport research in their field as well as optimal transport researchers willing to find applications for their numerical algorithms.
  • Thumbnail Image
    Item
    Volumetric Multi-View Rendering
    (The Eurographics Association and John Wiley & Sons Ltd., 2022) Fraboni, Basile; Webanck, Antoine; Bonneel, Nicolas; Iehl, Jean-Claude; Chaine, Raphaƫlle; Kim, Min H.
    Rendering photo-realistic images using Monte Carlo path tracing often requires sampling a large number of paths to reach acceptable levels of noise. This is particularly the case when rendering participating media, that complexify light paths with multiple scattering events. Our goal is to accelerate the rendering of heterogeneous participating media by exploiting redundancy across views, for instance when rendering animated camera paths, motion blur in consecutive frames or multi-view images such as lenticular or light-field images. This poses a challenge as existing methods for sharing light paths across views cannot handle heterogeneous participating media and classical estimators are not optimal in this context. We address these issues by proposing three key ideas. First, we propose new volume shift mappings to transform light paths from one view to another within the recently introduced null-scattering framework, taking into account changes in density along the transformed path. Second, we generate a shared path suffix that best contributes to a subset of views, thus effectively reducing variance. Third, we introduce the multiple weighted importance sampling estimator that benefits from multiple importance sampling for combining sampling strategies, and from weighted importance sampling for reducing the variance due to non contributing strategies. We observed significant reuse when views largely overlap, with no visible bias and reduced variance compared to regular path tracing at equal time. Our method further readily integrates into existing volumetric path tracing pipelines.