EG2017

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https://diglib.eg.org/handle/10.2312/2631246

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Partitioning Surfaces into Quad Patches
(The Eurographics Association, 2017) Campen, Marcel; Adrien Bousseau and Diego Gutierrez
The efficient and practical representation and processing of geometrically or topologically complex shapes often demands some form of virtual partitioning into pieces, each of which is of a simpler nature. Due to their regularity, highly structured networks of conforming quadrilateral patches, called quad layouts, or in particular instances quad meshes, are most beneficial in many scenarios; they enable the use of tensor-product representations based on NURBS or Bézier patches, grid-based multiresolution techniques, or discrete pixel-based map representations. However, partitions of this type are particularly complicated to create due to the inherent structural restrictions. Research in geometry processing has led to a variety of automatic or semi-automatic approaches to address this problem. This course provides a detailed introduction to this range of methods, treats their strengths and weaknesses, discusses their applicability and practical limitations, and outlines open problems in this field.
bRenderer: A Flexible Basis for a Modern Computer Graphics Curriculum
(The Eurographics Association, 2017) Bürgisser, Benjamin; Steiner, David; Pajarola, Renato; Jean-Jacques Bourdin and Amit Shesh
In this article, we present bRenderer, a basic educational 3D rendering framework that has resulted from four years of experience in teaching an introductory-level computer graphics course at the University of Zurich. Our renderer is based on the observation that teaching a single basic but comprehensive computer graphics course often means to face the choice between students learning a low-level graphics API bottom-up on one side, or a powerful (game) engine on the other. Solutions between these two extremes tend to be either too rudimentary to easily allow advanced visual effects in student projects, or too abstract to facilitate learning about the underlying principles of computer graphics. Our platform-independent framework abstracts the functionality of its underlying graphics API and libraries to an extent that still preserves the main concepts taught in a computer graphics course. Consequently, bRenderer can be used in student projects, as well as in exercises. It helps students to easily understand how a renderer is implemented without getting distracted by the particular implementation of the framework or platform-specific characteristics.
From 3D Models to 3D Prints: An Overview of the Processing Pipeline
(The Eurographics Association and John Wiley & Sons Ltd., 2017) Livesu, Marco; Ellero, Stefano; Martínez, Jonàs; Lefebvre, Sylvain; Attene, Marco; Victor Ostromoukov and Matthias Zwicker
Due to the wide diffusion of 3D printing technologies, geometric algorithms for Additive Manufacturing are being invented at an impressive speed. Each single step along the processing pipeline that prepares the 3D model for fabrication can now count on dozens of methods, that analyse and optimize geometry and machine instructions for various objectives. This report provides a classification of this huge state of the art, and elicits the relation between each single algorithm and a list of desirable objectives during model preparation - a process globally refereed to as Process Planning. The objectives themselves are listed and discussed, along with possible needs for tradeoffs. Additive Manufacturing technologies are broadly categorized to explicitly relate classes of devices and supported features. Finally, this report offers an analysis of the state of the art while discussing open and challenging problems from both an academic and an industrial perspective.
Parameter Estimation of BSSRDF for Heterogeneous Materials
(The Eurographics Association, 2017) Sone, Hiroki; Hachisuka, Toshiya; Koike, Takafumi; Adrien Peytavie and Carles Bosch
Rendering of highly scattering media is computationally expensive in general. While existing BSSRDF models can accurately and efficiently approximate light scattering in homogeneous media, we still have to resort to costly Monte Carlo simulation for heterogeneous media. We propose a simple parameter estimation method which enables homogeneous BSSRDF models to approximate the appearance of heterogeneous media. The main idea is to estimate the input optical parameters of a given homogeneous BSSRDF model such that the output well approximates light transport within heterogeneous media. Our method takes spatially varying optical coefficients into account by taking averages of the coefficients around the incident and exitant points. This approach is motivated by the path integral theory which predicts how wide the beam of light will spread in heterogeneous media. Since our method provides parameters for homogeneous BSSRDF models, it is applicable to many existing BSSRDF models and easy to integrate into existing rendering systems. We show that our modification produces more accurate results than the existing heuristics with the same goal.
Variable k-buffer using Importance Maps
(The Eurographics Association, 2017) Vasilakis, Andreas-Alexandros; Vardis, Konstantinos; Papaioannou, Georgios; Moustakas, Konstantinos; Adrien Peytavie and Carles Bosch
Successfully predicting visual attention can significantly improve many aspects of computer graphics and games. Despite the thorough investigation in this area, selective rendering has not addressed so far fragment visibility determination problems. To this end, we present the first ''selective multi-fragment rendering'' solution that alters the classic k-buffer construction procedure from a fixed-k to a variable-k per-pixel fragment allocation guided by an importance-driven model. Given a fixed memory budget, the idea is to allocate more fragment layers in parts of the image that need them most or contribute more significantly to the visual result. An importance map, dynamically estimated per frame based on several criteria, is used for the distribution of the fragment layers across the image. We illustrate the effectiveness and quality superiority of our approach in comparison to previous methods when performing order-independent transparency rendering in various, high depth-complexity, scenarios.
AnimDiff: Comparing 3D Animations for Revision Control
(The Eurographics Association, 2017) Madges, George; Miles, Idris; Anderson, Eike Falk; Adrien Peytavie and Carles Bosch
The process of animating a complex 3D character can be a time consuming activity which may take several iterations and several artists working in collaboration, each iteration improving some elements of the animation but potentially introducing artifacts in others. At present there exists no formal process to collate these various revisions in a manner that allows for close examination of their differences, which would help speed up the creation of 3D animations. To address this we present a method for equivalence checking and displaying differences between differing versions of an animated 3D model. Implemented in a tool that allows selective blending of animations, this provides a first step towards a 3D animation revision control system.
EUROGRAPHICS 2017: Dirk Bartz Prize Frontmatter
(Eurographics Association, 2017) Bruckner, Stefan; Ropinski, Timo;
Using Activity Led Learning for Teaching Computer Graphics Principles Through Augmented Reality
(The Eurographics Association, 2017) Liarokapis, Fotis; Jean-Jacques Bourdin and Amit Shesh
In this paper, an activity-led learning approach is applied to computer graphics students at Masaryk University for the Master's course called "Augmented Reality Interfaces". The scope of this research is to demonstrate the learning effectiveness of augmented reality and project development approaches for higher education teaching. Students were presented with the theoretical background in augmented reality in the classical way (lectures) and were asked to implement the assignment using active learning approaches. The aim of the assignment was to design and implement an augmented reality interface demonstrating various computer graphics aspects which could be used to enhance the teaching process. Their main focus was to concentrate on three aspects: interface design, interaction mediums and collaboration aspects. Data was collected for two consecutive academic years (one semester with 13 weeks per year) and results showed a very high pass-rate as well as increased engagement and student satisfaction. However, students found that this sort of approach is harder than other approaches.
Stroke Style Transfer
(The Eurographics Association, 2017) Shaheen, Sara; Ghanem, Bernard; Adrien Peytavie and Carles Bosch
We propose a novel method to transfer sketch style at the stroke level from one free-hand line drawing to another, whereby these drawings can be from different artists. It aims to transfer the style of the input sketch at the stroke level to the style encountered in sketches by other artists. This is done by modifying all the parametric stroke segments in the input, so as to minimize a global stroke-level distance between the input and target styles. To do this, we exploit a recent work on stroke authorship recognition to define the stroke-level distance [SRG15], which is in turn minimized using conventional optimization tools. We showcase the quality of style transfer qualitatively by applying the proposed technique on several input-target combinations.
Generating ASCII-Art: A Nifty Assignment from a Computer Graphics Programming Course
(The Eurographics Association, 2017) Anderson, Eike Falk; Jean-Jacques Bourdin and Amit Shesh
We present a graphics application programming assignment from an introductory programming course with a computer graphics focus. This assignment involves simple image-processing, asking students to write a conversion program that turns images into ASCII Art. Assessment of the assignment is simplified through the use of an interactive grading tool.
Robust Blending and Occlusion Compensation in Dynamic Multi-Projection Mapping
(The Eurographics Association, 2017) Lange, Vanessa; Siegl, Christian; Colaianni, Matteo; Stamminger, Marc; Bauer, Frank; Adrien Peytavie and Carles Bosch
Using multi-projection systems allows us to immerse users in an altered reality without the need to wear additional head-gear. The immersion of such systems relies on the quality of the calibration which in general will degenerate over time when used outside of a lab environment. This work introduces a novel balance term that allows us to hide high frequency brightness seams caused by self-shadowing of the projected geometry and the borders of the projection frustum. We further use this more robust blending between projectors to compensate for occluding spectators, who enter the projection volume, by filling the resulting shadows with light from other projectors.
State of the Art in Methods and Representations for Fabrication-Aware Design
(The Eurographics Association and John Wiley & Sons Ltd., 2017) Bermano, Amit Haim; Funkhouser, Thomas; Rusinkiewicz, Szymon; Victor Ostromoukov and Matthias Zwicker
Computational manufacturing technologies such as 3D printing hold the potential for creating objects with previously undreamed-of combinations of functionality and physical properties. Human designers, however, typically cannot exploit the full geometric (and often material) complexity of which these devices are capable. This STAR examines recent systems developed by the computer graphics community in which designers specify higher-level goals ranging from structural integrity and deformation to appearance and aesthetics, with the final detailed shape and manufacturing instructions emerging as the result of computation. It summarizes frameworks for interaction, simulation, and optimization, as well as documents the range of general objectives and domain-specific goals that have been considered. An important unifying thread in this analysis is that different underlying geometric and physical representations are necessary for different tasks: we document over a dozen classes of representations that have been used for fabrication-aware design in the literature. We analyze how these classes possess obvious advantages for some needs, but have also been used in creative manners to facilitate unexpected problem solutions.
Swung-to-Cylinder Projection for Panoramic Image Viewing
(The Eurographics Association, 2017) Chang, Che-Han; Lai, Wei-Sheng; Chuang, Yung-Yu; Pierre Benard and Daniel Sykora
This paper proposes the swung-to-cylinder projection model for mapping a sphere to a plane, which is useful for viewing 360 panoramic images. Our model extends the swung-to-plane model and consists of two steps. In the first step, the sphere is projected onto a swung surface. In the second step, the projected image on the swung surface is mapped onto a cylinder through the perspective projection. The proposed model is simple, efficient and easy to control. Similar to the swung-to-plane model, it makes a better compromise between distortion minimization and line preserving. However, it does not suffer from the distortion problem of the swung-to-plane model when viewing full 360 panoramic images.
A Comparative Review of Tone-mapping Algorithms for High Dynamic Range Video
(The Eurographics Association and John Wiley & Sons Ltd., 2017) Eilertsen, Gabriel; Mantiuk, Rafal K.; Unger, Jonas; Victor Ostromoukov and Matthias Zwicker
Tone-mapping constitutes a key component within the field of high dynamic range (HDR) imaging. Its importance is manifested in the vast amount of tone-mapping methods that can be found in the literature, which are the result of an active development in the area for more than two decades. Although these can accommodate most requirements for display of HDR images, new challenges arose with the advent of HDR video, calling for additional considerations in the design of tone-mapping operators (TMOs). Today, a range of TMOs exist that do support video material.We are now reaching a point where most camera captured HDR videos can be prepared in high quality without visible artifacts, for the constraints of a standard display device. In this report, we set out to summarize and categorize the research in tone-mapping as of today, distilling the most important trends and characteristics of the tone reproduction pipeline. While this gives a wide overview over the area, we then specifically focus on tone-mapping of HDR video and the problems this medium entails. First, we formulate the major challenges a video TMO needs to address. Then, we provide a description and categorization of each of the existing video TMOs. Finally, by constructing a set of quantitative measures, we evaluate the performance of a number of the operators, in order to give a hint on which can be expected to render the least amount of artifacts. This serves as a comprehensive reference, categorization and comparative assessment of the state-of-the-art in tone-mapping for HDR video.
Conformal Factor Persistence for Fast Hierarchical Cone Extraction
(The Eurographics Association, 2017) Vintescu, Ana-Maria; Dupont, Florent; Lavoué, Guillaume; Memari, Pooran; Tierny, Julien; Adrien Peytavie and Carles Bosch
This paper presents a new algorithm for the fast extraction of hierarchies of cone singularities for conformal surface parameterization. Cone singularities have been shown to greatly improve the distortion of such parameterizations since they locally absorb the area distortion. Therefore, existing automatic approaches aim at inserting cones where large area distortion can be predicted. However, such approaches are iterative, which results in slow computations, even often slower than the actual subsequent parameterization procedure. This becomes even more problematic as often the user does not know in advance the right number of needed cones and thus needs to explore cone hierarchies to obtain a satisfying result. Our algorithm relies on the key observation that the local extrema of the conformal factor already provide a good approximation of the cone singularities extracted with previous techniques, while needing only one linear solving where previous approaches needed one solving per hierarchy level. We apply concepts from persistent homology to organize very efficiently such local extrema into a global hierarchy. Experiments demonstrate the approximation quality of our approach quantitatively and report time-performance improvements of one order of magnitude, which makes our technique well suited for interactive contexts.
The New CGEMS - Preparing the Computer Graphics Educational Materials Source to Meet the Needs of Educators
(The Eurographics Association, 2017) Anderson, Eike Falk; Duchowski, Andrew; Liarokapis, Fotis; Redford, Adam; Jean-Jacques Bourdin and Amit Shesh
ACM SIGGRAPH and Eurographics are restarting CGEMS, the Computer Graphics Educational Materials Source, an on-line repository of curricular material for computer graphics education. In this context, the question that we ask ourselves is: ''How can CGEMS best meet the needs of educators''? The aim of this forum is to provide the audience with an idea of the purpose of CGEMS - a source of educational materials for educators by educators - and to give them an opportunity to contribute their views and ideas towards shaping the new CGEMS. Towards this purpose, we have identified a number of issues to resolve, which the panel will put forward to the participants of the forum for discussion.
Phong Tessellation and PN Polygons for Polygonal Models
(The Eurographics Association, 2017) Hettinga, Gerben J.; Kosinka, Jiri; Adrien Peytavie and Carles Bosch
We extend Phong tessellation and point normal (PN) triangles from the original triangular setting to arbitrary polygons by use of generalised barycentric coordinates and S-patches. In addition, a generalisation of the associated quadratic normal field is given as well as a simple algorithm for evaluating the polygonal extensions for a polygon with vertex normals on the GPU.
High Quality and Efficient Direct Rendering of Massive Real-world Point Clouds
(The Eurographics Association, 2017) Bouchiba, Hassan; Groscot, Raphaël; Deschaud, Jean-Emmanuel; Goulette, François; Pierre Benard and Daniel Sykora
We present a novel real-time screen-space rendering algorithm for real-world 3D scanned datasets. Our method takes advantage of the pull phase of a pull-push pyramidal filling algorithm in order to feed a hidden point removal operator. The push phase is then used to fill the final framebuffer. We demonstrate on a real-world complex dataset that our method produces better visual results and is more efficient comparing to state of the art algorithms.
"Synchronize" to VR Body: Full Body Illusion in VR Space
(The Eurographics Association, 2017) Xiong, Peikun; Sun, Chen; Cai, Dongsheng; Adrien Peytavie and Carles Bosch
Virtual Reality (VR) becomes accessible to mimic a "real-like" world now. People who have a VR experience usually can be impressed by the immersive feeling, they might consider themselves are actually existed in the VR space. Self-consciousness is important for people to identify their own characters in VR space, and illusory ownership can help people to "build" their "bodies". The rubber hand illusion can convince us a fake hand made by rubber is a part of our bodies under certain circumstances. Researches about autoscopic phenomena extend this illusory to the so-called full body illusion. We conducted 3 type of experiments to study the illusory ownership in VR space as it shows in Figure 1, and we learned: Human body must receive the synchronized visual signal and somatosensory stimulus at the same time; The visual signal must be the first person perceptive; the subject and the virtual body needs to be the same height as much as possible. All these illusory ownerships accompanied by the body temperature decreases, where the body is stimulated.
An Automatic Stroke Extraction Method using Manifold Learning
(The Eurographics Association, 2017) Chen, Xudong; Lian, Zhouhui; Tang, Yingmin; Xiao, Jianguo; Adrien Peytavie and Carles Bosch
Stroke extraction is one of the most important tasks in areas of computer graphics and document analysis. So far, data-driven methods are believed to perform relatively well, which use the pre-processed characters as templates. However, how to accurately extract strokes of characters is still a tough and challenging task because there are various styles of characters, which may vary a lot from the template character. To solve this problem, we build a font skeleton manifold in which we can always find a most similar character as a template by traversing the locations in the manifold. Because of the similar structure and font style, the point set registration of the template character with the target character would be much more effective and accurate. Experimental results on characters in both printing style and handwriting style reveal that our method using manifold learning has a better performance in the application of stroke extraction for Chinese characters.

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