EG2016

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https://diglib.eg.org/handle/10.2312/15062

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Interactive Modeling of Support-free Shapes for Fabrication
(The Eurographics Association, 2016) Reiner, Tim; Lefebvre, Sylvain; T. Bashford-Rogers and L. P. Santos
We introduce an interactive sculpting approach that enables modeling of support-free objects: objects which do not require any support structures during 3D printing. We propose three operators - trim, preserve, grow - to maintain the support-free property during interactive modeling. These operators let us define brushes that perform either in an unconstrained manner (adapting the shape to the brush effect), or selectively discard changes inside the brush volume. Our technique can be applied to many modeling operations and we demonstrate it on brushes for adding or removing matter. We describe an efficient implementation of a voxel-based modeling tool that produces only support-free shapes, and show example shapes modeled within minutes.
Tiled Depth of Field Splatting
(The Eurographics Association, 2016) Selgrad, Kai; Franke, Linus; Stamminger, Marc; Luis Gonzaga Magalhaes and Rafal Mantiuk
We present a method to compute post-processing depth of field (DOF) that produces more accurate results than previous approaches. Our method is based on existing approaches, namely DOF rendering by splatting and fast, tile-based particle accumulation. Using tile-based accumulation allows us to correctly sort out of focus pixels and apply proper alpha-blending to avoid artifacts commonly encountered with filter-based depth of field methods.
Buoyancy Optimization for Computational Fabrication
(The Eurographics Association and John Wiley & Sons Ltd., 2016) Wang, Lingfeng; Whiting, Emily; Joaquim Jorge and Ming Lin
This paper introduces a design and fabrication pipeline for creating floating forms. Our method optimizes for buoyant equilibrium and stability of complex 3D shapes, applying a voxel-carving technique to control the mass distribution. The resulting objects achieve a desired floating pose defined by a user-specified waterline height and orientation. In order to enlarge the feasible design space, we explore novel ways to load the interior of a design using prefabricated components and casting techniques. 3D printing is employed for high-precision fabrication. For larger scale designs we introduce a method for stacking lasercut planar pieces to create 3D objects in a quick and economic manner. We demonstrate fabricated designs of complex shape in a variety of floating poses.
Mesh Saliency Analysis via Local Curvature Entropy
(The Eurographics Association, 2016) Limper, Max; Kuijper, Arjan; Fellner, Dieter W.; T. Bashford-Rogers and L. P. Santos
We present a novel approach for estimating mesh saliency. Our method is fast, flexible, and easy to implement. By applying the well-known concept of Shannon entropy to 3D mesh data, we obtain an efficient method to determine mesh saliency. Comparing our method to the most recent, state-of-the-art approach, we show that results of at least similar quality can be achieved within a fraction of the original computation time. We present saliency-guided mesh simplification as a possible application.
A Practical and Controllable Hair and Fur Model for Production Path Tracing
(The Eurographics Association and John Wiley & Sons Ltd., 2016) Chiang, Matt Jen-Yuan; Bitterli, Benedikt; Tappan, Chuck; Burley, Brent; Joaquim Jorge and Ming Lin
We present an energy-conserving fiber shading model for hair and fur that is efficient enough for path tracing. Our model adopts a near-field formulation to avoid the expensive integral across the fiber, accounts for all high order internal reflection events with a single lobe, and proposes a novel, closed-form distribution for azimuthal roughness based on the logistic distribution. Additionally, we derive, through simulation, a parameterization that relates intuitive user controls such as multiple-scattering albedo and isotropic cylinder roughness to the underlying physical parameters.
A Simple and Effective Method to Detect Orthogonal Vanishing Points in Uncalibrated Images of Man-Made Environments
(The Eurographics Association, 2016) Simon, Gilles; Fond, Antoine; Berger, Marie-Odile; T. Bashford-Rogers and L. P. Santos
This paper presents an effective and easy-to-implement algorithm to compute orthogonal vanishing points in uncalibrated images of man-made scenes. The main contribution is to estimate the zenith and the horizon line before detecting the vanishing points, using simple properties of the central projection and exploiting accumulations of oriented segments around the horizon. Our method is fast and yields an accuracy comparable, and even better in some cases, to that of state-of-the-art algorithms.
Inertial Steady 2D Vector Field Topology
(The Eurographics Association and John Wiley & Sons Ltd., 2016) Günther, Tobias; Theisel, Holger; Joaquim Jorge and Ming Lin
Vector field topology is a powerful and matured tool for the study of the asymptotic behavior of tracer particles in steady flows. Yet, it does not capture the behavior of finite-sized particles, because they develop inertia and do not move tangential to the flow. In this paper, we use the fact that the trajectories of inertial particles can be described as tangent curves of a higher dimensional vector field. Using this, we conduct a full classification of the first-order critical points of this higher dimensional flow, and devise a method to their efficient extraction. Further, we interactively visualize the asymptotic behavior of finite-sized particles by a glyph visualization that encodes the outcome of any initial condition of the governing ODE, i.e., for a varying initial position and/or initial velocity. With this, we present a first approach to extend traditional vector field topology to the inertial case.
VBTC: GPU-Friendly Variable Block Size Texture Encoding
(The Eurographics Association and John Wiley & Sons Ltd., 2016) Krajcevski, Pavel; Golas, Abhinav; Ramani, Karthik; Shebanow, Michael; Manocha, Dinesh; Joaquim Jorge and Ming Lin
Recent advances in computer graphics have relied on high-quality textures in order to generate photorealistic real-time images. Texture compression standards meet these growing demands for data, but current texture compression schemes use fixed-rate methods where statically sized blocks of pixels are represented using the same numbers of bits irrespective of their data content. In order to account for the natural variation in detail, we present an alternative format that allows variable bit-rate texture compression with minimal changes to texturing hardware. Our proposed scheme uses one additional level of indirection to allow the variation of the block size across the same texture. This single change is exploited to both vary the amount of bits allocated to certain parts of the texture and to duplicate redundant texture information across multiple pixels. To minimize hardware changes, the method picks combinations of block sizes and compression methods from existing fixed-rate standards. With this approach, our method is able to demonstrate energy savings of up to 50%, as well as higher quality compressed textures over current state of the art techniques.
DeepProp: Extracting Deep Features from a Single Image for Edit Propagation
(The Eurographics Association and John Wiley & Sons Ltd., 2016) Endo, Yuki; Iizuka, Satoshi; Kanamori, Yoshihiro; Mitani, Jun; Joaquim Jorge and Ming Lin
Edit propagation is a technique that can propagate various image edits (e.g., colorization and recoloring) performed via user strokes to the entire image based on similarity of image features. In most previous work, users must manually determine the importance of each image feature (e.g., color, coordinates, and textures) in accordance with their needs and target images. We focus on representation learning that automatically learns feature representations only from user strokes in a single image instead of tuning existing features manually. To this end, this paper proposes an edit propagation method using a deep neural network (DNN). Our DNN, which consists of several layers such as convolutional layers and a feature combiner, extracts strokeadapted visual features and spatial features, and then adjusts the importance of them. We also develop a learning algorithm for our DNN that does not suffer from the vanishing gradient problem, and hence avoids falling into undesirable locally optimal solutions. We demonstrate that edit propagation with deep features, without manual feature tuning, can achieve better results than previous work.
Building Construction Sets by Tiling Grammar Simplification
(The Eurographics Association and John Wiley & Sons Ltd., 2016) Kalojanov, Javor; Wand, Michael; Slusallek, Philipp; Joaquim Jorge and Ming Lin
This paper poses the problem of fabricating physical construction sets from example geometry: A construction set provides a small number of different types of building blocks from which the example model as well as many similar variants can be reassembled. This process is formalized by tiling grammars. Our core contribution is an approach for simplifying tiling grammars such that we obtain physically manufacturable building blocks of controllable granularity while retaining variability, i.e., the ability to construct many different, related shapes. Simplification is performed by sequences of two types of elementary operations: non-local joint edge collapses in the tile graphs reduce the granularity of the decomposition and approximate replacement operations reduce redundancy. We evaluate our method on abstract graph grammars in addition to computing several physical construction sets, which are manufactured using a commodity 3D printer.
Generalized Diffusion Curves: An Improved Vector Representation for Smooth-Shaded Images
(The Eurographics Association and John Wiley & Sons Ltd., 2016) Jeschke, Stefan; Joaquim Jorge and Ming Lin
This paper generalizes the well-known Diffusion Curves Images (DCI), which are composed of a set of Bezier curves with colors specified on either side. These colors are diffused as Laplace functions over the image domain, which results in smooth color gradients interrupted by the Bezier curves. Our new formulation allows for more color control away from the boundary, providing a similar expressive power as recent Bilaplace image models without introducing associated issues and computational costs. The new model is based on a special Laplace function blending and a new edge blur formulation. We demonstrate that given some user-defined boundary curves over an input raster image, fitting colors and edge blur from the image to the new model and subsequent editing and animation is equally convenient as with DCIs. Numerous examples and comparisons to DCIs are presented.
Automatic Portrait Segmentation for Image Stylization
(The Eurographics Association and John Wiley & Sons Ltd., 2016) Shen, Xiaoyong; Hertzmann, Aaron; Jia, Jiaya; Paris, Sylvain; Price, Brian; Shechtman, Eli; Sachs, Ian; Joaquim Jorge and Ming Lin
Portraiture is a major art form in both photography and painting. In most instances, artists seek to make the subject stand out from its surrounding, for instance, by making it brighter or sharper. In the digital world, similar effects can be achieved by processing a portrait image with photographic or painterly filters that adapt to the semantics of the image. While many successful user-guided methods exist to delineate the subject, fully automatic techniques are lacking and yield unsatisfactory results. Our paper first addresses this problem by introducing a new automatic segmentation algorithm dedicated to portraits. We then build upon this result and describe several portrait filters that exploit our automatic segmentation algorithm to generate high-quality portraits.
Geometry and Attribute Compression for Voxel Scenes
(The Eurographics Association and John Wiley & Sons Ltd., 2016) Dado, Bas; Kol, Timothy R.; Bauszat, Pablo; Thiery, Jean-Marc; Eisemann, Elmar; Joaquim Jorge and Ming Lin
Voxel-based approaches are today's standard to encode volume data. Recently, directed acyclic graphs (DAGs) were successfully used for compressing sparse voxel scenes as well, but they are restricted to a single bit of (geometry) information per voxel. We present a method to compress arbitrary data, such as colors, normals, or reflectance information. By decoupling geometry and voxel data via a novel mapping scheme, we are able to apply the DAG principle to encode the topology, while using a palette-based compression for the voxel attributes, leading to a drastic memory reduction. Our method outperforms existing state-of-the-art techniques and is well-suited for GPU architectures. We achieve real-time performance on commodity hardware for colored scenes with up to 17 hierarchical levels (a 128K3 voxel resolution), which are stored fully in core.
Directional Field Synthesis, Design, and Processing
(The Eurographics Association and John Wiley & Sons Ltd., 2016) Vaxman, Amir; Campen, Marcel; Diamanti, Olga; Panozzo, Daniele; Bommes, David; Hildebrandt, Klaus; Ben-Chen, Mirela; Joaquim Madeira and Gustavo Patow
Direction fields and vector fields play an increasingly important role in computer graphics and geometry processing. The synthesis of directional fields on surfaces, or other spatial domains, is a fundamental step in numerous applications, such as mesh generation, deformation, texture mapping, and many more. The wide range of applications resulted in definitions for many types of directional fields: from vector and tensor fields, over line and cross fields, to frame and vector-set fields. Depending on the application at hand, researchers have used various notions of objectives and constraints to synthesize such fields. These notions are defined in terms of fairness, feature alignment, symmetry, or field topology, to mention just a few. To facilitate these objectives, various representations, discretizations, and optimization strategies have been developed. These choices come with varying strengths and weaknesses. This report provides a systematic overview of directional field synthesis for graphics applications, the challenges it poses, and the methods developed in recent years to address these challenges.
3D Characters for Virtual Reality
(The Eurographics Association, 2016) Orvalho, Veronica; Runa, Catarina; Lewis, John P.; Augusto Sousa and Kadi Bouatouch
Creating a 3D avatar that looks like a specific person is timeconsuming, requires expert artists, expensive equipment and a complex pipeline. In this tutorial we explain the different stages of a traditional character animation pipeline: modeling, rigging and animation. But, most important we describe how each of this stages bind together and which are the challenges developers face today at each stage. Our ultimate goal is to explain stepbystep the creation of a unified facial animation pipeline. We build the tutorial over our experience on what worked, what didn't work, why we did what we did and how we are planning to improve in the future. Given the popularity of Virtual Reality since the launching of Oculus Rift, we also describe how a traditional animation pipeline can be applied in Virtual Reality, it's challenges, limitations and potential. Throughout the tutorial we introduce the theoretical background for character animation and present the current state of the art in this field. Last, we aim to trigger a discussion to analyse different lines of research that emerge by bringing together traditional character animation and Virtual Reality.
Peripheral Retinal Image Simulation Based on Retina Shapes
(The Eurographics Association, 2016) Dias, Catarina; Wick, Michael; Rifai, Katharina; Wahl, Siegfried; T. Bashford-Rogers and L. P. Santos
We present a method to render the image of a scene reaching the retina, the retinal image, taking into account human offaxis optical aberrations. To this end, we consider realistic wide-angle eye models that offer an anatomical description of the refractive structures of the eye as a set of lenses and accurately reproduce the optical aberrations in the periphery. We then combine these with representative retinal shapes and with distributed ray tracing. Due to the interplay between the eye model and the curved retina, we obtain a realistic simulation of the retinal image, not only foveally but also in the periphery.
EUROGRAPHICS 2016: Tutorials Frontmatter
(Eurographics Association, 2016) Sousa, A. Augusto; Bouatouch, Kadi;
The HDR-video Pipeline
(The Eurographics Association, 2016) Unger, Jonas; Banterle, Francesco; Eilertsen, Gabriel; Mantiuk, Rafał K.; Augusto Sousa and Kadi Bouatouch
High dynamic range (HDR) video technology has gone through remarkable developments over the last few years; HDR-video cameras are being commercialized, new algorithms for color grading and tone mapping specifically designed for HDR-video have recently been proposed, and the first open source compression algorithms for HDR- video are becoming available. HDR-video represents a paradigm shift in imaging and computer graphics, which has and will continue to generate a range of both new research challenges and applications. This intermediate- level tutorial will give an in-depth overview of the full HDR-video pipeline present several examples of state-of- the-art algorithms and technology in HDR-video capture, tone mapping, compression and specific applications in computer graphics.
Interactive Monte-Carlo Ray-Tracing Upsampling
(The Eurographics Association, 2016) Boughida, Malik; Groueix, Thibault; Boubekeur, Tamy; Luis Gonzaga Magalhaes and Rafal Mantiuk
We propose a practical method to approximate global illumination at interactive framerates for dynamic scenes. We address multi-bounce, visibility-aware indirect lighting, for diffuse to moderately glossy materials, relying on GPU-accelerated raytracing for this purpose. While Monte-Carlo ray-tracing algorithms offer unbiased results, they produce images which are, under interactive constraints, extremely noisy, even with GPU acceleration. Unfortunately, filtering them to reach visual appeal induces a large kernel, which is not compatible with interactive framerate. We address this problem using a simple downsampling approach. First, we trace indirect paths on a uniformly distributed subset of pixels, decorrelating diffuse and specular components of lighting. Then, we perform a joint bilateral upsampling on both components, taking inspiration from deferred shading by driving this upsampling with a full-resolution G-Buffer. Our solution provides smooth results, does not require any pre-computations, and is both easy to implement and flexible, as it can be used with any generation strategy for indirect rays.
Trajectory Data Visualization on Mobile Devices with Animated Maps
(The Eurographics Association, 2016) Gonçalves, Tiago; Afonso, Ana Paula; Ferreira, António; Vieira, Ana Rita; T. Bashford-Rogers and L. P. Santos
With the increasing popularity of mobile devices (like smartphones and tablets) and georeferenced applications, more people record and analyse their own movement data. This pattern is noticeable with the increasing usage of mobile applications that, in addition to record the evolution of a person's location over time, also allow the visualization of that information, typically, in the form of 2D static maps, complemented with various representations to extract knowledge from the data. Despite the various studies addressing spatio-temporal data visualization, its application on mobile devices for the representation of personal trajectory data is still somewhat unexplored. Animated maps have been proposed as a potential intuitive and appealing technique for the visualization of information in a dynamic way, particularly for the detection of spatio-temporal data relations. We aim to address these issues by presenting a comparative study between static and animated representations of human movement on a mobile device context. Our results suggest that although it may not significantly improve user understanding of the data, the use of animated maps is a preferred and less interactively demanding option over static maps.

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