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A General Illumination Model for Molecular Visualization

computer graphics FORUM 2018年第3期37卷 367-378页

作者： Hermosilla, P. Vazquez, P. Vinacua, A. Ropinski, T. Ulm Univ Visual Comp Grp Ulm Germany Univ Politecn Cataluna VIRVIG Grp Barcelona Spain

Several visual representations have been developed over the years to visualize molecular structures, and to enable a better understanding of their underlying chemical processes. Today, the most frequently used atom-based representations are the Space-filling, the Solvent Excluded Surface, the Balls-and-Sticks, and the Licorice models. While each of these representations has its individual benefits, when applied to large-scale models spatial arrangements can be difficult to interpret when employing current visualization techniques. In the past it has been shown that global illumination techniques improve the perception of molecular visualizations;unfortunately existing approaches are tailored towards a single visual representation. We propose a general illumination model for molecular visualization that is valid for different representations. With our illumination model, it becomes possible, for the first time, to achieve consistent illumination among all atom-based molecular representations. The proposed model can be further evaluated in real-time, as it employs an analytical solution to simulate diffuse light interactions between objects. To be able to derive such a solution for the rather complicated and diverse visual representations, we propose the use of regression analysis together with adapted parameter sampling strategies as well as shape parametrization guided sampling, which are applied to the geometric building blocks of the targeted visual representations. We will discuss the proposed sampling strategies, the derived illumination model, and demonstrate its capabilities when visualizing several dynamic molecules.

关键词： CCS Concepts •Human‐centered computing → Scientific visualization •computing methodologies → computer graphics Rendering

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Instant Stippling on 3D Scenes

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computer graphics FORUM 2018年第7期37卷 255-266页

作者： Ma, Lei Guo, Jianwei Yan, Dong-Ming Sun, Hanqiu Chen, Yanyun Chinese Acad Sci Inst Software State Key Lab Comp Sci Beijing Peoples R China Chinese Acad Sci Inst Automat NLPR Beijing Peoples R China Univ Chinese Acad Sci Beijing Peoples R China Chinese Univ Hong Kong Hong Kong Hong Kong Peoples R China

In this paper, we present a novel real-time approach to generate high-quality stippling on 3D scenes. The proposed method is built on a precomputed 2D sample sequence called incremental Voronoi set with blue-noise properties. A rejection sampling scheme is then applied to achieve tone reproduction, by thresholding the sample indices proportional to the inverse target tonal value to produce a suitable stipple density. Our approach is suitable for stippling large-scale or even dynamic scenes because the thresholding of individual stipples is trivially parallelizable. In addition, the static nature of the underlying sequence benefits the frame-to-frame coherence of the stippling. Finally, we propose an extension that supports stipples of varying sizes and tonal values, leading to smoother spatial and temporal transitions. Experimental results reveal that the temporal coherence and real-time performance of our approach are superior to those of previous approaches.

关键词： CCS Concepts •computing methodologies → computer graphics Non‐photorealistic rendering Image processing Texturing Appearance and texture representations

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Deep Video Stabilization Using Adversarial Networks

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computer graphics FORUM 2018年第7期37卷 267-276页

作者： Xu, Sen-Zhe Hu, Jun Wang, Miao Mu, Tai-Jiang Hu, Shi-Min Tsinghua Univ Dept Comp Sci & Technol Beijing Peoples R China

Video stabilization is necessary for many hand-held shot videos. In the past decades, although various video stabilization methods were proposed based on the smoothing of 2D, 2.5D or 3D camera paths, hardly have there been any deep learning methods to solve this problem. Instead of explicitly estimating and smoothing the camera path, we present a novel online deep learning framework to learn the stabilization transformation for each unsteady frame, given historical steady frames. Our network is composed of a generative network with spatial transformer networks embedded in different layers, and generates a stable frame for the incoming unstable frame by computing an appropriate affine transformation. We also introduce an adversarial network to determine the stability of apiece of video. The network is trained directly using the pair of steady and unsteady videos. Experiments show that our method can produce similar results as traditional methods, moreover, it is capable of handling challenging unsteady video of low quality, where traditional methods fail, such as video with heavy noise or multiple exposures. Our method runs in real time, which is much faster than traditional methods.

关键词： CCS Concepts •computing methodologies → computer graphics

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Monte Carlo Methods for Volumetric Light Transport Simulation

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computer graphics FORUM 2018年第2期37卷 551-576页

作者： Novak, Jan Georgiev, Iliyan Hanika, Johannes Jarosz, Wojciech Disney Res Zurich Switzerland Solid Angle Zurich Switzerland Karlsruhe Inst Technol Karlsruhe Germany Dartmouth Coll Hanover NH 03755 USA

The wide adoption of path-tracing algorithms in high-end realistic rendering has stimulated many diverse research initiatives. In this paper we present a coherent survey of methods that utilize Monte Carlo integration for estimating light transport in scenes containing participating media. Our work complements the volume-rendering state-of-the-art report by Cerezo et al. [CPP*05];we review publications accumulated since its publication over a decade ago, and include earlier methods that are key for building light transport paths in a stochastic manner. We begin by describing analog and non-analog procedures for free-path sampling and discuss various expected-value, collision, and track-length estimators for computing transmittance. We then review the various rendering algorithms that employ these as building blocks for path sampling. Special attention is devoted to null-collision methods that utilize fictitious matter to handle spatially varying densities;we import two next-flight estimators originally developed in nuclear sciences. Whenever possible, we draw connections between image-synthesis techniques and methods from particle physics and neutron transport to provide the reader with a broader context.

关键词： CCS Concepts •computing methodologies → computer graphics Rendering Ray tracing

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Exploiting Repetitions for Image-Based Rendering of Facades

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computer graphics FORUM 2018年第4期37卷 119-131页

作者： Rodriguez, Simon Bousseau, Adrien Durand, Fredo Drettakis, George Univ Cote Azur Inria Nice France MIT CSAIL Cambridge MA USA

Street-level imagery is now abundant but does not have sufficient capture density to be usable for Image-Based Rendering (IBR) of facades. We present a method that exploits repetitive elements in facades - such as windows - to perform data augmentation, in turn improving camera calibration, reconstructed geometry and overall rendering quality for IBR. The main intuition behind our approach is that a few views of several instances of an element provide similar information to many views of a single instance of that element. We first select similar instances of an element from 3-4 views of a facade and transform them into a common coordinate system, creating a "platonic" element. We use this common space to refine the camera calibration of each view of each instance and to reconstruct a 3D mesh of the element with multi-view stereo, that we regularize to obtain a piecewise-planar mesh aligned with dominant image contours. Observing the same element under multiple views also allows us to identify reflective areas - such as glass panels - which we use at rendering time to generate plausible reflections using an environment map. Our detailed 3D mesh, augmented set of views, and reflection mask enable image-based rendering of much higher quality than results obtained using the input images directly.

关键词： CCS Concepts •computing methodologies → computer graphics Image‐based rendering Reconstruction

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Landscaper: A Modeling System for 3D Printing Scale Models of Landscapes

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computer graphics FORUM 2018年第3期37卷 439-451页

作者： Allahverdi, K. Djavaherpour, H. Mahdavi-Amiri, A. Samavati, F. Univ Calgary Calgary AB Canada Simon Fraser Univ Burnaby BC Canada

Landscape models of geospatial regions provide an intuitive mechanism for exploring complex geospatial information. However, the methods currently used to create these scale models require a large amount of resources, which restricts the availability of these models to a limited number of popular public places, such as museums and airports. In this paper, we have proposed a system for creating these physical models using an affordable 3D printer in order to make the creation of these models more widely accessible. Our system retrieves GIS relevant to creating a physical model of a geospatial region and then addresses the two major limitations of affordable 3D printers, namely the limited number of materials and available printing volume. This is accomplished by separating features into distinct extruded layers and splitting large models into smaller pieces, allowing us to employ different methods for the visualization of different geospatial features, like vegetation and residential areas, in a 3D printing context. We confirm the functionality of our system by printing two large physical models of relatively complex landscape regions.

关键词： CCS Concepts •computing methodologies → computer graphics

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Uncut Aerial Video via a Single Sketch

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computer graphics FORUM 2018年第7期37卷 191-199页

作者： Yang, Hao Xie, Ke Huang, Shengqiu Huang, Hui Shenzhen Univ Shenzhen Peoples R China

Nowadays UAV filming is getting popular, more and more stunning aerial videos appearing online. Nonetheless, making a good uncut aerial video with only one-long-shot for the large-scale outdoor scenes is still quite challenging, no many eye-catching pieces available yet. It requires users to have both consummate drone controlling skill and good perception of filming aesthetics. If totally manual, the user has to simultaneously adjust the drone position and the mounted camera orientation during the whole flyby while trying to keep all operation changes executed smoothly. Recent research has proposed a number of planning tools for automatic or semi-automatic aerial videography, however, most requires rather complex user inputs and heavy computations. In this paper, we propose a user-friendly system designed to simplify the input and automatically generate continuous camera moves to capture compelling aerial videos that users prefer to see without any post cutting or editing. Assume a rough 2.5D scene model that includes all the regions of interest are available, users are only required to casually draw a single sketch on the 2D map. Our system will analyze this rough sketch input, compute the corresponding quality views in 3D safe flying zone, and then create a globally optimal camera trajectory passing through regions of user interest via solving a combinatorial problem. At end, we optimize the drone flying speed locally to make the resulting aerial videos more visually pleasing.

关键词： CCS Concepts •computing methodologies → computer graphics graphics systems and interfaces Interest point and saliency detections

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An Efficient Solver for Two-way Coupling Rigid Bodies with Incompressible Flow

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computer graphics FORUM 2018年第8期37卷 59-68页

作者： Aanjaneya, Mridul Rutgers State Univ Dept Comp Sci New Brunswick NJ 08901 USA

We present an efficient solver for monolithic two-way coupled simulation of rigid bodies with incompressible fluids that is robust to poor conditioning of the coupled system in the presence of large density ratios between the solid and the fluid. Our method leverages ideas from the theory of Domain Decomposition, and uses a hybrid combination of direct and iterative solvers that exploits the low-dimensional nature of the solid equations. We observe that a single Multigrid V-cycle for the fluid equations serves as a very effective preconditioner for solving the Schur-complement system using Conjugate Gradients, which is the main computational bottleneck in our pipeline. We use spectral analysis to give some theoretical insights behind this observation. Our method is simple to implement, is entirely assembly-free besides the solid equations, allows for the use of large time steps because of the monolithic formulation, and remains stable even when the iterative solver is terminated early. We demonstrate the efficacy of our method on several challenging examples of two-way coupled simulation of smoke and water with rigid bodies. To illustrate that our method is applicable to other problems, we also show an example of underwater bubble simulation.

关键词： CCS Concepts •computing methodologies → computer graphics Physical simulation

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