EG2023
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Item Towards L-System Captioning for Tree Reconstruction(The Eurographics Association, 2023) Magnusson, Jannes S.; Hilsmann, Anna; Eisert, Peter; Babaei, Vahid; Skouras, MelinaThis work proposes a novel concept for tree and plant reconstruction by directly inferring a Lindenmayer-System (L-System) word representation from image data in an image captioning approach. We train a model end-to-end which is able to translate given images into L-System words as a description of the displayed tree. To prove this concept, we demonstrate the applicability on 2D tree topologies. Transferred to real image data, this novel idea could lead to more efficient, accurate and semantically meaningful tree and plant reconstruction without using error-prone point cloud extraction, and other processes usually utilized in tree reconstruction. Furthermore, this approach bypasses the need for a predefined L-System grammar and enables species-specific L-System inference without biological knowledge.Item Non-Separable Multi-Dimensional Network Flows for Visual Computing(The Eurographics Association, 2023) Ehm, Viktoria; Cremers, Daniel; Bernard, Florian; Singh, Gurprit; Chu, Mengyu (Rachel)Flows in networks (or graphs) play a significant role in numerous computer vision tasks. The scalar-valued edges in these graphs often lead to a loss of information and thereby to limitations in terms of expressiveness. For example, oftentimes highdimensional data (e.g. feature descriptors) are mapped to a single scalar value (e.g. the similarity between two feature descriptors). To overcome this limitation, we propose a novel formalism for non-separable multi-dimensional network flows. By doing so, we enable an automatic and adaptive feature selection strategy - since the flow is defined on a per-dimension basis, the maximizing flow automatically chooses the best matching feature dimensions. As a proof of concept, we apply our formalism to the multi-object tracking problem and demonstrate that our approach outperforms scalar formulations on the MOT16 benchmark in terms of robustness to noise.Item Multi-Display Ray Tracing Framework(The Eurographics Association, 2023) Romero Calla, Luciano Arnaldo; Mohanto, Bipul; Pajarola, Renato; Staadt, Oliver; Singh, Gurprit; Chu, Mengyu (Rachel)We present a framework that will provide a highly efficient and scalable multi-display ray-tracing based rendering system capable of utilizing multiple GPU devices to produce high-quality images. Our system integrates advanced technologies, including MPI, CUDA, CUDA IPC, OptiX 7.6, and C++, resulting in a cutting-edge solution for interactive rendering.Item Photogrammetric Reconstruction of a Stolen Statue(The Eurographics Association, 2023) Liu, Zishun; Doubrovski, Eugeni L.; Geraedts, Jo M. P.; Wang, Wenting; Yam, Yeung; Wang, Charlie C. L.; Babaei, Vahid; Skouras, MelinaIn this paper, we propose a method to reconstruct a digital 3D model of a stolen/damaged statue using photogrammetric methods. This task is challenging because the number of available photos for a stolen statue is in general very limited - especially the side/back view photos. Besides using standard structure-from-motion and multi-view stereo methods, we match image pairs with low overlap using sliding windows and maximize the normalized cross-correlation (NCC) based patch-consistency so that the image pairs can be well aligned into a complete model to build the 3D mesh surface. Our method is based on the prior of the planar side on the statue's pedestal, which can cover a large range of statues. We hope this work will motivate more research efforts for the reconstruction of those stolen/damaged statues and heritage preservation.Item Luminance-Preserving and Temporally Stable Daltonization(The Eurographics Association, 2023) Ebelin, Pontus; Crassin, Cyril; Denes, Gyorgy; Oskarsson, Magnus; Åström, Kalle; Akenine-Möller, Tomas; Babaei, Vahid; Skouras, MelinaWe propose a novel, real-time algorithm for recoloring images to improve the experience for a color vision deficient observer. The output is temporally stable and preserves luminance, the most important visual cue. It runs in 0.2 ms per frame on a GPU.Item EUROGRAPHICS 2023: Posters Frontmatter(Eurographics Association, 2023) Singh, Gurprit; Chu, Mengyu (Rachel); Singh, Gurprit; Chu, Mengyu (Rachel)Item Parameter-Free and Improved Connectivity for Point Clouds(The Eurographics Association, 2023) Marin, Diana; Ohrhallinger, Stefan; Wimmer, Michael; Singh, Gurprit; Chu, Mengyu (Rachel)Determining connectivity in unstructured point clouds is a long-standing problem that is still not addressed satisfactorily. In this poster, we propose an extension to the proximity graph introduced in [MOW22] to three-dimensional models. We use the spheres-of-influence (SIG) proximity graph restricted to the 3D Delaunay graph to compute connectivity between points. Our approach shows a better encoding of the connectivity in relation to the ground truth than the k-nearest neighborhood (kNN) for a wide range of k values, and additionally, it is parameter-free. Our result for this fundamental task offers potential for many applications relying on kNN, e.g., improvements in normal estimation, surface reconstruction, motion planning, simulations, and many more.Item Towards a Formal Education of Visual Effects Artists(The Eurographics Association, 2023) Redford, Adam; Anderson, Eike Falk; Magana, Alejandra; Zara, JiriThe rapid growth of the visual effects industry over the past three decades and increasing demand for high quality visual effects for film, television and similar media, in turn increasing demand for graduates in this field have highlighted the need for formal education in visual effects. In this paper, we explore the design of a visual effects undergraduate degree programme and discuss our aims and objectives in implementing this programme in terms of both curriculum and syllabus.Item PointCloudSlicer: Gesture-based Segmentation of Point Clouds(The Eurographics Association, 2023) Gowtham, Hari Hara; Parakkat, Amal Dev; Cani, Marie-Paule; Babaei, Vahid; Skouras, MelinaSegmentation is a fundamental problem in point-cloud processing, addressing points classification into consistent regions, the criteria for consistency being based on the application. In this paper, we introduce a simple, interactive framework enabling the user to quickly segment a point cloud in a few cutting gestures in a perceptually consistent way. As the user perceives the limit of a shape part, they draw a simple separation stroke over the current 2D view. The point cloud is then segmented without needing any intermediate meshing step. Technically, we find an optimal, perceptually consistent cutting plane constrained by user stroke and use it for segmentation while automatically restricting the extent of the cut to the closest shape part from the current viewpoint. This enables users to effortlessly segment complex point clouds from an arbitrary viewpoint with the possibility of handling self-occlusions.Item Project Elements: A Computational Entity-component-system in a Scene-graph Pythonic Framework, for a Neural, Geometric Computer Graphics Curriculum(The Eurographics Association, 2023) Papagiannakis, George; Kamarianakis, Manos; Protopsaltis, Antonis; Angelis, Dimitris; Zikas, Paul; Magana, Alejandra; Zara, JiriWe present the Elements project, a lightweight, open-source, computational science and computer graphics (CG) framework, tailored for educational needs, that offers, for the first time, the advantages of an Entity-Component-System (ECS) along with the rapid prototyping convenience of a Scenegraph-based pythonic framework. This novelty allows advances in the teaching of CG: from heterogeneous directed acyclic graphs and depth-first traversals, to animation, skinning, geometric algebra and shader-based components rendered via unique systems all the way to their representation as graph neural networks for 3D scientific visualization. Taking advantage of the unique ECS in a a Scenegraph underlying system, this project aims to bridge CG curricula and modern game engines (MGEs), that are based on the same approach but often present these notions in a black-box approach. It is designed to actively utilize software design patterns, under an extensible open-source approach. Although Elements provides a modern (i.e., shader-based as opposed to fixed-function OpenGL), simple to program approach with Jupyter notebooks and unit-tests, its CG pipeline is not black-box, exposing for teaching for the first time unique challenging scientific, visual and neural computing concepts.Item Game-based Transformations: A Playful Approach to Learning Transformations in Computer Graphics(The Eurographics Association, 2023) Eisemann, Martin; Magana, Alejandra; Zara, JiriIn this paper, we present a playful and game-based learning approach to teaching transformations in a second-year undergraduate computer graphics course. While the theoretical concepts were taught in class, the exercise consists of two web-based tools that help the students to get a playful grasp on the complex topic, which is the foundation for many of the later concepts typically taught in computer graphics, such as the rendering pipeline, animation, camera motion, shadow mapping and many more. The final students' projects and feedback indicate that the game-based introduction was well-received by the students.Item Effective User Studies in Computer Graphics(The Eurographics Association, 2023) Malpica, Sandra; Sun, Qi; Kellnhofer, Petr; Beacco, Alejandro; Senel, Gizem; McDonnell, Rachel; Flores Vargas, Mauricio; Serrano, Ana; Slusallek, PhilippUser studies are a useful tool for researchers, allowing them to collect data on how users perceive, interact with and process different types of sensory information. If planned in advance, user experiments can be leveraged in every stage of a research project, from early design, prototyping and feature exploration to applied proofs of concept, passing through validation and data collection for model training. User studies can provide the researcher with different types of information depending on the chosen methodology: user performance metrics, surveys and interviews, field studies, physiological data, etc. Considering human perception and other cognitive processes is particularly important in computer graphics, where most research produces outputs whose ultimate purpose is to be seen or perceived by a human. Being able to measure in an objective and systematic way how the information we generate is integrated into the representational space humans create to situate themselves in the world means that researchers will have more information to implement optimal algorithms, tools and techniques. In this tutorial we will give an overview of good practices for user studies in computer graphics with a particular focus on virtual reality use cases. We will cover the basics on how to design, carry out and analyze good user studies, as well as different particularities to be taken into account in immersive environments.Item Efficient Needle Insertion Simulation using Hybrid Constraint Solver and Isolated DOFs(The Eurographics Association, 2023) Martin, Claire; Zeng, Ziqiu; Courtecuisse, Hadrien; Babaei, Vahid; Skouras, MelinaThis paper introduces a real-time compatible method to improve the location of constraints between a needle and tissues in the context of needle insertion simulation. This method is based on intersections between the Finite Element (FE) meshes of the needle and the tissues. It is coupled with the method of isolating mechanical DOFs and a hybrid solver (implying both direct and iterative resolutions) to respectively generate and solve the constraint problem while reducing the computation time.Item Velocity-Based LOD Reduction in Virtual Reality: A Psychophysical Approach(The Eurographics Association, 2023) Petrescu, David; Warren, Paul A.; Montazeri, Zahra; Pettifer, Steve; Babaei, Vahid; Skouras, MelinaVirtual Reality headsets enable users to explore the environment by performing self-induced movements. The retinal velocity produced by such motion reduces the visual system's ability to resolve fine detail. We measured the impact of self-induced head rotations on the ability to detect quality changes of a realistic 3D model in an immersive virtual reality environment. We varied the Level of Detail (LOD) as a function of rotational head velocity with different degrees of severity. Using a psychophysical method, we asked 17 participants to identify which of the two presented intervals contained the higher quality model under two different maximum velocity conditions. After fitting psychometric functions to data relating the percentage of correct responses to the aggressiveness of LOD manipulations, we identified the threshold severity for which participants could reliably (75%) detect the lower LOD model. Participants accepted an approximately four-fold LOD reduction even in the low maximum velocity condition without a significant impact on perceived quality, suggesting that there is considerable potential for optimisation when users are moving (increased range of perceptual uncertainty). Moreover, LOD could be degraded significantly more (around 84%) in the maximum head velocity condition, suggesting these effects are indeed speed-dependent.Item Automatic Step Size Relaxation in Sphere Tracing(The Eurographics Association, 2023) Bán, Róbert; Valasek, Gábor; Babaei, Vahid; Skouras, MelinaWe propose a robust auto-relaxed sphere tracing method that automatically scales its step sizes based on data from previous iterations. It possesses a scalar hyperparemeter that is used similarly to the learning rate of gradient descent methods. We show empirically that this scalar degree of freedom has a smaller effect on performance than the step-scale hyperparameters of concurrent sphere tracing variants. Additionally, we compare the performance of our algorithm to these both on procedural and discrete signed distance input and show that it outperforms or performs up to par to the most efficient method, depending on the limit on iteration counts. We also verify that our method takes significantly fewer robustness-preserving sphere trace fallback steps, as it generates fewer invalid, over-relaxed step sizes.Item Synthetic Dataset for Panic Detection in Human Crowded Scenes(The Eurographics Association, 2023) Calle, Javier; Leskovsky, Peter; Garcia, Jorge; Sanchez, Marti; Singh, Gurprit; Chu, Mengyu (Rachel)AI is increasingly being used in public protection by using crowd anomaly detection. This is useful for identifying panic events enabling control forces to act faster. A significant challenge in this field is the lack of data for training these algorithms. Recreating panic events with big crowds can be both expensive and hazardous. To address this issue, this paper proposes the creation of a synthetic dataset for crowd panic behaviour. The process involves defining the scenario and setting up the appropriate CCTV cameras. Many scenarios are prepared, including variations in weather conditions. Next is the scene population with pedestrians and vehicles, with different crowd sizes and vehicle trajectories. To recreate panic, the behaviour of each person is programmed. The final videos show normality situations before the panic events start. Finally, we achieved 1717 simulations.Item Tight Bounding Boxes for Voxels and Bricks in a Signed Distance Field Ray Tracer(The Eurographics Association, 2023) Hansson-Söderlund, Herman; Akenine-Möller, Tomas; Babaei, Vahid; Skouras, MelinaWe present simple methods to compute tight axis-aligned bounding boxes for voxels and for bricks of voxels in a signed distance function renderer based on ray tracing. Our results show total frame time reductions of 20-31% in a real-time path tracer.Item EUROGRAPHICS 2023: Tutorials Frontmatter(Eurographics Association, 2023) Serrano, Ana; Slusallek, Philipp; Serrano, Ana; Slusallek, PhilippItem Using Vulkan for Graphics Research(The Eurographics Association, 2023) Castorina, Marco; Sassone, Gabriel; Serrano, Ana; Slusallek, PhilippThe Vulkan API has has been released in 2016 and it has continued to evolve to include the latest hardware capabilities. Compared to OpenGL, it is a more verbose API that requires a deeper knowledge of the underlying hardware architecture. While this can make the API more difficult to get started with, it also rewards developers with finer grained control over resource management, multi-threading and work submission. This flexibility allows developers to achieve better performance over older APIs and opens the door to novel techniques that would have been harder, if not impossible, to implement before. In this tutorial we are going to provide an introduction to the core Vulkan API concepts and how they map to the underlying hardware. We are going to demonstrate how to leverage async compute to overlap graphics and compute work for better performance. We will provide detailed examples that make use of cutting-edge features like Mesh Shaders and Ray Tracing to achieve state of the art results in real-time rendering.Item EUROGRAPHICS 2023: Short Papers Frontmatter(Eurographics Association, 2023) Babaei, Vahid; Skouras, Melina; Babaei, Vahid; Skouras, Melina