Wavelet Point‐Based Global Illumination

Abstract

b) WPBGI (c) BPT (a) PBGI Figure 1: Compared to traditional PBGI (a), our approach (b) models accurately non-diffuse indirect lighting effects and appears as an efficient substitute to bidirectional path tracing (c), trading a moderate image degradation for up to a 10x speed-up in our experiments. AbstractPoint-Based Global Illumination (PBGI) is a popular rendering method in special effects and motion picture productions. This algorithm provides a diffuse global illumination solution by caching radiance in a mesh-less hierarchical data structure during a pre-process, while solving for visibility over this cache, at rendering time and for each receiver, using microbuffers, which are localized depth and color buffers inspired from real time rendering environments. As a result, noise free ambient occlusion, indirect soft shadows and color bleeding effects are computed efficiently for high resolution image output and in a temporally coherent fashion. We propose an evolution of this method to address the case of non-diffuse inter-reflections and refractions. While the original PBGI algorithm models radiance using spherical harmonics, we propose to use wavelets parameterized on the direction space to better localize the radiance representation in the presence of highly directional reflectance. We also propose a new importance-driven adaptive microbuffer model to capture accurately incoming radiance at a point. Furthermore, we evaluate outgoing radiance using a fast wavelet radiance product and contain the induced larger memory footprint by encoding hierarchically the wavelets in the PBGI tree. As a result, our algorithm can handle non-lambertian BSDF in the light transport simulation, reproducing caustics and multiple reflections/refractions bounces with a similar quality to bidirectional path tracing in a large number of cases and for only a fraction of its computation time. Our approach is simple to implement and easy to integrate into any existing PBGI framework, with an intuitive control on the approximation error. We evaluate it on a collection of example scenes.

Point-Based Rendering for Homogeneous Participating Media with Refractive Boundaries

“…This is not an issue in our test scenes, but could be in other scenes. The solution would be to use microbuffers [3], [40], [41].…”

High Dynamic Range Point Clouds for Real‐Time Relighting

“…The use of larger micro‐buffers mitigates these issues, but this solution increases the rendering time. An alternative solution could be the use of an importance sampling strategy during the construction of a micro‐buffer as proposed by Ritschel et al [REG∗ 09] or adaptive micro‐buffers [WMB15]. Our results lack of any kind of self occlusion effect.…”

“…This algorithm is free from noise, accounts for long‐range indirect lighting and reproduces an important subset of GI effects. Its evolutions demonstrate high scalability for parallel architectures [REG∗ 09, HREB11] and out‐of‐core execution [Tab12], robustness to compression [BB12] and factorization [WHB∗ 13], the ability, to a certain extent, to cope with nondiffuse effects [WMB15], and scalability to render complex scenes from a very large number of viewpoints [KBLE19]. Our key observation is that a 3D scanning colored point cloud already provides the input of a PBGI tree avoiding the significant amount of work requested at caching time.…”