Visibility sweeps for joint-hierarchical importance sampling of direct lighting for stochastic volume rendering

Physically-based light transport in heterogeneous volumetric data is computationally expensive because the rendering integral (particularly visibility) has to be stochastically solved. We present a visibility estimation method in concert with an importance-sampling technique for efficient and unbiased stochastic volume rendering. Our solution relies on a joint strategy, which involves the environmental illumination and visibility inside of the volume. A major contribution of our method is a fast sweeping-plane algorithm to progressively estimate partial occlusions at discrete locations, where we store the result using an octahedral representation. We then rely on a quadtree-based hierarchy to perform a joint importance sampling. Our technique is unbiased, requires little precomputation, is highly parallelizable, and is applicable to a various volume data sets, dynamic transfer functions, and changing environmental lighting.Intelligent SystemsElectrical Engineering, Mathematics and Computer Scienc

Next Event Estimation++: Visibility Mapping for Efficient Light Transport Simulation

Monte-Carlo rendering requires determining the visibility between scene points as the most common and compute intense operation to establish paths between camera and light source. Unfortunately, many tests reveal occlusions and the corresponding paths do not contribute to the final image. In this work, we present next event estimation++ (NEE++): a visibility mapping technique to perform visibility tests in a more informed way by caching voxel to voxel visibility probabilities. We show two scenarios: Russian roulette style rejection of visibility tests and direct importance sampling of the visibility. We show applications to next event estimation and light sampling in a uni-directional path tracer, and light-subpath sampling in Bi-Directional Path Tracing. The technique is simple to implement, easy to add to existing rendering systems, and comes at almost no cost, as the required information can be directly extracted from the rendering process itself. It discards up to 80% of visibility tests on average, while reducing variance by 20% compared to other state-of-the-art light sampling techniques with the same number of samples. It gracefully handles complex scenes with efficiency similar to Metropolis light transport techniques but with a more uniform convergence.Comp Graphics & Visualisatio

Interactive Black-Hole Visualization

We present an efficient algorithm for visualizing the effect of black holes on its distant surroundings as seen from an observer nearby in orbit. Our solution is GPU-based and builds upon a two-step approach, where we first derive an adaptive grid to map the 360-view around the observer to the distorted celestial sky, which can be directly reused for different camera orientations. Using a grid, we can rapidly trace rays back to the observer through the distorted spacetime, avoiding the heavy workload of standard tracing solutions at real-time rates. By using a novel interpolation technique we can also simulate an observer path by smoothly transitioning between multiple grids. Our approach accepts real star catalogues and environment maps of the celestial sky and generates the resulting black-hole deformations in real time.Accepted Author ManuscriptComp Graphics & Visualisatio

Conservative Ray Batching using Geometry Proxies

We present a method for improving batched ray traversal as was presented by Pharr et al. [PKGH97]. We propose to use conservative proxy geometry to more accurately determine whether a ray has a possibility of hitting any geometry that is storedon disk. This prevents unnecessary disk loads and thus reduces the disk bandwidth.Comp Graphics & Visualisatio

Directed Acyclic Graph Encoding for Compressed Shadow Maps

Detailed shadows in large-scale environments are challenging. Our approach enables efficient detailed shadow computations for static environments at a low memory cost. It builds upon compressed precomputed multiresolution hierarchies but uses a directed acyclic graph to encode its tree structure. Further, depth values are compressed and stored separately and we use a bit-plane encoding for the lower tree levels entries in order to further reduce memory requirements and increase locality. We achieve between 20% to 50% improved compression rates, while retaining high performance.Comp Graphics & Visualisatio

Geometric Sample Reweighting for Monte Carlo Integration

Numerical integration is fundamental in multiple Monte Carlo rendering problems. We present a sample reweighting scheme, including underlying theory, and analysis of numerical performance for the integration of an unknown one-dimensional function. Our method is simple to implement and builds upon the insight to link the weights to a function reconstruction process during integration. We provide proof that our solution is unbiased in one-dimensional cases and consistent in multi-dimensional cases. We illustrate its effectiveness in several use cases.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Comp Graphics & Visualisatio

Foreword to the special section on Pacific Graphics 2020

Comp Graphics & Visualisatio

Effects of inter-reflections on the chromatic structure of the light field

Chromatic properties of the effective light in a space are hard to predict, measure and visualise. This is due to complex interactions between materials and illuminants. Here, we describe, measure and visualise the effects of inter-reflections on the structure of the physical light field for diffusely scattering scenes. The spectral properties of inter-reflections vary as a function of the number of bounces they went through. Via a computational model, these spectral variations were found to be systematic and correspond with brightness, saturation and hue shifts. We extended our light-field methods to measure and understand these spectral effects on the first-order properties of light fields, the light density and light vector. We tested the model via a set of computer renderings and cubic spectral illuminance measurements in mock-up rooms under different furnishing scenarios for two types of illuminants. The predicted spectral variations were confirmed and indeed varied systematically within the resulting light field, spatially and directionally. Inter-reflections predominantly affect the light density spectrum and have less impact on the light vector spectrum. It is important to consider these differential effects for their consequences on the colour rendering of 3-dimensional objects and people.Comp Graphics & VisualisationHuman Information Communication Desig

Smooth, Interactive Rendering Techniques on Large-Scale, Geospatial Data in Flood Visualizations

Visualising large-scale geospatial data is a demanding challenge that finds applications in many fields, including climatology and hydrology. Due to the enormous data size, it is currently not possible to render full datasets interactively without significantly compromising quality (especially not when information changes over time). In this paper, we present new approaches to render and interact with detail-varying Light Detection and Range (LiDAR) point sets. Furthermore, our approach allows the attachment of large-scale geospatial meta information and the modification of point attributes on the fly. The core of our algorithm is a dynamic GPU-based hierarchical tree data structure that is used in conjunction with an out-of-core, Levelof-Detail (LoD)-Point-based Rendering (PBR) algorithm to modify data on the fly. This combination makes it possible to augment the original data with dynamic context information that can be used to highlight features (e.g.,routes, marked areas) or to reshape the entire data set in real-time. We showcase the usefulness of our algorithm in the context of disaster management and illustrate how decision makers can discuss a flood scenario covering a large area (spanning 300 km2) and discuss hazards, as well as related protection measures, interactively. One of our presented reference point sets includes parts of the AHN2 data set (14 TB of LiDAR data in total). Previous rendering algorithms relied on a long offline preprocessing (several hours) to ensure a quick data display. This step made any changes to the data impossible. With our new approach, we can modify point sets without requiring a new preprocessing run.Intelligent SystemsElectrical Engineering, Mathematics and Computer Scienc

Gradient-Guided Local Disparity Editing

Stereoscopic 3D technology gives visual content creators a new dimension of design when creating images and movies. While useful for conveying emotion, laying emphasis on certain parts of the scene, or guiding the viewer's attention, editing stereo content is a challenging task. Not respecting comfort zones or adding incorrect depth cues, for example depth inversion, leads to a poor viewing experience. In this paper, we present a solution for editing stereoscopic content that allows an artist to impose disparity constraints and removes resulting depth conflicts using an optimization scheme. Using our approach, an artist only needs to focus on important high-level indications that are automatically made consistent with the entire scene while avoiding contradictory depth cues and respecting viewer comfort.Comp Graphics & Visualisatio