Computer Graphics & Visual Computing (CGVC) 2019

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https://diglib.eg.org/handle/10.2312/2632803

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Robust and Flexible Puzzle Solving with Corner-based Cycle Consistent Correspondences
(The Eurographics Association, 2019) Wang, T.; Vladimirov, K.; Goh, S.; Lai, Y.-K.; Xie, X.; Tam, G. K. L.; Vidal, Franck P. and Tam, Gary K. L. and Roberts, Jonathan C.
Solving jigsaw puzzles is a classic problem in computer vision with various applications. Over the past decades, many useful approaches have been introduced. Most existing works use edge-wise similarity measures for assembling puzzles with square pieces of the same size, and recent work innovates to use the loop constraint to improve efficiency and accuracy. We observe that most existing techniques cannot be easily extended to puzzles with rectangular pieces of arbitrary sizes, and no existing loop constraints can be used to model such challenging scenarios. In this paper, we propose a new corner-wise matching approach, modelled using the MatchLift framework to solve square puzzles with cycle consistency. We further show one exciting example illustrating how puzzles with rectangular pieces of arbitrary sizes would be solved by our technique.
Hash-based Hierarchical Caching for Interactive Previews in Global Illumination Rendering
(The Eurographics Association, 2019) Roth, Thorsten; Weier, Martin; Bauszat, Pablo; Hinkenjann, André; Li, Yongmin; Vidal, Franck P. and Tam, Gary K. L. and Roberts, Jonathan C.
Modern Monte-Carlo-based rendering systems still suffer from the computational complexity involved in the generation of noise-free images, making it challenging to synthesize interactive previews. We present a framework suited for rendering such previews of static scenes using a caching technique that builds upon a linkless octree. Our approach allows for memory-efficient storage and constant-time lookup to cache diffuse illumination at multiple hitpoints along the traced paths. Non-diffuse surfaces are dealt with in a hybrid way in order to reconstruct view-dependent illumination while maintaining interactive frame rates. By evaluating the visual fidelity against ground truth sequences and by benchmarking, we show that our approach compares well to low-noise path traced results, but with a greatly reduced computational complexity allowing for interactive frame rates. This way, our caching technique provides a useful tool for global illumination previews and multi-view rendering.
A Somatic Approach to Combating Cybersickness Utilising Airflow Feedback
(The Eurographics Association, 2019) Harrington, Jake; Williams, Benjamin; Headleand, Christopher; Vidal, Franck P. and Tam, Gary K. L. and Roberts, Jonathan C.
Abstract This paper presents a novel somatosensory approach towards reducing the risk of cybersickness during virtual reality locomotion in a 3D environment. We start by presenting theories regarding the cause of cybersickness which led to the proposal and construction of a prototype airflow-based feedback system. The solution proposed by this paper builds on the concept of sensory misalignment, where the body struggles understand its state due to conflicting sensory feedback and consequently generates negative health symptoms and discomfort. To evaluate the work an experiment was carried out where 40 participants drive a simulated car around a virtual environment. In one condition the participants had additional somatosensory feedback regarding their motion, provided by a fan synchronised to their speed in the virtual world. In the second condition there was no additional feedback. We evaluated both conditions for cybersickness and presence, and showed a statistically significant improvement for both in the condition using airflow feedback. We conclude with a discussion of the results, and present a direction for possible future research.
Generating High Fidelity Surface Meshes of Neocortical Neurons using Skin Modifiers
(The Eurographics Association, 2019) Abdellah, Marwan; Favreau, Cyrille; Hernando, Juan; Lapere, Samuel; Schürmann, Felix; Vidal, Franck P. and Tam, Gary K. L. and Roberts, Jonathan C.
We present the results of exploring the capabilities of skinning modifiers to generate high fidelity polygonal surface meshes of neurons from their morphological skeletons that are segmented from optical microscopy slides. Our algorithm is implemented in Blender as an add-on relying on its standard Python API. The implementation is also integrated into an open source domain specific framework, NeuroMorphoVis, that is used to visualize and analyze neuronal morphologies available from the neuroscientific community. Our technique is applied to create meshes for a set of neurons with 55 different morphologies reconstructed from the neocortex of a 14-days-old rat. The generated meshes are used to visualize full compartmental simulations of neocortical activity for analysis purposes and also to create high quality scientific illustrations of in silico neuronal circuits for media production with physically-based path tracers.
Projectional Radiography Simulator: an Interactive Teaching Tool
(The Eurographics Association, 2019) Sujar, Aaron; Kelly, Graham; García, Marcos; Vidal, Franck; Vidal, Franck P. and Tam, Gary K. L. and Roberts, Jonathan C.
Radiographers need to know a broad range of knowledge about X-ray radiography, which can be specific to each part of the body. Due to the harmfulness of the ionising radiation used, teaching and training using real patients is not ethical. Students have limited access to real X-ray rooms and anatomic phantoms during their studies. Books, and now web apps, containing a set of static pictures are then often used to illustrate clinical cases. In this study, we have built an Interactive X-ray Projectional Simulator using a deformation algorithm with a real-time X-ray image simulator. Users can load various anatomic models and the tool enables virtual model positioning in order to set a specific position and see the corresponding X-ray image. It allows teachers to simulate any particular X-ray projection in a lecturing environment without using real patients and avoiding any kind of radiation risk. This tool also allows the students to reproduce the important parameters of a real X-ray machine in a safe environment. We have performed a face and content validation in which our tool proves to be realistic (72% of the participants agreed that the simulations are visually realistic), useful (67%) and suitable (78%) for teaching X-ray radiography.
Assisting Serious Games Level Design with an Augmented Reality Application and Workflow
(The Eurographics Association, 2019) Beever, Lee; Pop, Serban; John, Nigel W.; Vidal, Franck P. and Tam, Gary K. L. and Roberts, Jonathan C.
With the rise in popularity of serious games there is an increasing demand for virtual environments based on real-world locations. Emergency evacuation or fire safety training are prime examples of serious games that would benefit from accurate location depiction together with any application involving personal space. However, creating digital indoor models of real-world spaces is a difficult task and the results obtained by applying current techniques are often not suitable for use in real-time virtual environments. To address this problem, we have developed an application called LevelEd AR that makes indoor modelling accessible by utilizing consumer grade technology in the form of Apple's ARKit and a smartphone. We compared our system to that of a tape measure and a system based on an infra-red depth sensor and application. We evaluated the accuracy and efficiency of each system over four different measuring tasks of increasing complexity. Our results suggest that our application is more accurate than the depth sensor system and as accurate and more time efficient as the tape measure over several tasks. Participants also showed a preference to our LevelEd AR application over the depth sensor system regarding usability. Finally, we carried out a preliminary case study that demonstrates how LevelEd AR can be successfully used as part of current industry workflows for serious games level design.
Virtual Reality Callouts - Demonstrating Knowledge With Spatial-Related Textual Information
(The Eurographics Association, 2019) Horst, Robin; Degreif, Anika; Mathy, Marvin; Dörner, Ralf; Vidal, Franck P. and Tam, Gary K. L. and Roberts, Jonathan C.
Virtual (VR) and augmented reality (AR) can bring an added value during the demonstration of knowledge, as for example within an interactive research demo. Callouts are strings of text which are connected by a line to a specific feature of an object. These visual annotations can be used during such demos and can be placed in different kinds of media, such as illustrations, technical drawings, images and videos. Callouts are also used in virtual 3D environments to anchor textual information to a specific point in space. Therefore they can be a valuable tool for virtually demonstrating knowledge. The alignment of callouts in such information rich environments is an elemental factor within the view management of the VR scene. In this paper we propose a concept for interactive microlearning application for knowledge demonstration that uses callouts as a fundamental element. We distinguish three types of interactive callout-representations by their alignment relative to the user, for being static or dynamic in their position and orientation. Within an implementation of the different callout versions we show the feasibility and in a user study we indicate a user-preference towards static positioned callouts.
Fast and Efficient Nearest Neighbor Search for Particle Simulations
(The Eurographics Association, 2019) Gross, Julian; Köster, Marcel; Krüger, Antonio; Vidal, Franck P. and Tam, Gary K. L. and Roberts, Jonathan C.
One of the fundamental algorithms in particle simulations is the identification and iteration over nearest neighbors of every particle. Well-known examples are SPH or PBD simulations that compute forces and particle-position updates in every simulation step. In order to find nearest neighbors for all particles, hash-based, grid-based or tree-based approaches have been developed in the past. The two most prominent and fastest algorithms use virtual and explicitly allocated uniform grids to achieve high performance on Graphics Processing Units (GPUs). However, they have disadvantages with numerous particle simulation domains, either in terms of run time or memory consumption. We present a novel algorithm that can be applied to large simulation domains that significantly reduces memory consumption using a shared-memory based neighbor search. Furthermore, we achieve high-performance on our evaluation scenarios that often outperforms existing state-of-the-art methods.
CGVC 2019: Frontmatter
(Eurographics Association, 2019) Vidal, Franck; Tam, Gary K. L.; Roberts, Jonathan C.; Vidal, Franck P. and Tam, Gary K. L. and Roberts, Jonathan C.
Colour Processing in Adversarial Attacks on Face Liveness Systems
(The Eurographics Association, 2019) Abduh, Latifah; Ivrissimtzis, Ioannis; Vidal, Franck P. and Tam, Gary K. L. and Roberts, Jonathan C.
In the context of face recognition systems, liveness test is a binary classification task aiming at distinguishing between input images that come from real people's faces and input images that come from photos or videos of those faces, and presented to the system's camera by an attacker. In this paper, we train the state-of-the-art, general purpose deep neural network ResNet for liveness testing, and measure the effect on its performance of adversarial attacks based on the manipulation of the saturation component of the imposter images. Our findings suggest that higher saturation values in the imposter images lead to a decrease in the network's performance. Next, we study the relationship between the proposed adversarial attacks and corresponding direct presentation attacks. Initial results on a small dataset of processed images which are then printed on paper or displayed on an LCD or a mobile phone screen, show that higher saturation values lead to higher values in the network's loss function, indicating that these colour manipulation techniques can indeed be converted into enhanced presentation attacks.
Deformed Reality
(The Eurographics Association, 2019) Petit, Antoine; Haouchine, Nazim; Roy, Frederick; Goldman, Daniel B.; Cotin, Stephane; Vidal, Franck P. and Tam, Gary K. L. and Roberts, Jonathan C.
We present Deformed Reality, a new way of interacting with an augmented reality environment by manipulating 3D objects in an intuitive and physically-consistent manner. Using the core principle of augmented reality to estimate rigid pose over time, our method makes it possible for the user to deform the targeted object while it is being rendered with its natural texture, giving the sense of a interactive scene editing. Our framework follows a computationally efficient pipeline that uses a proxy CAD model for both pose computation, physically-based manipulations and scene appearance estimation. The final composition is built upon a continuous image completion and re-texturing process to preserve visual consistency. The presented results show that our method can open new ways of using augmented reality by not only augmenting the environment but also interacting with objects intuitively.
Controlling 3D Visualisations with Multiple Degrees of Freedom
(The Eurographics Association, 2019) Sandoval, Mario; Morris, Tim; Turner, Martin; Vidal, Franck P. and Tam, Gary K. L. and Roberts, Jonathan C.
In this paper, the two major components of a new multi-layer framework ideal for two-handed interaction in desktop virtual environments called Library for Interactive Settings of User-Mode (LISU) are explained. In addition, we evaluate LISU performance with a group of participants and we report some of our initial results by giving an analysis of user experiences, and interaction speed.
Towards a Tool for the Creation of Micro-visualisations
(The Eurographics Association, 2019) Jackson, James; Ritsos, Panagiotis; Roberts, Jonathan; Vidal, Franck P. and Tam, Gary K. L. and Roberts, Jonathan C.
As the every day use of mobile and small screen devices becomes more common, it is necessary to explore how we can visualise data effectively in small design spaces. These screens are often used in situations where it is necessary to convey information in a concise, readable, reliable and visually appealing way. Our work focuses on the design and development of a tool to facilitate the creation and manipulation of new micro-visualisations. The results show that the tool is suitable for creating large number of outputs quickly and efficiently.
A Mesh Correspondence Approach for Efficient Animation Transfer
(The Eurographics Association, 2019) Moutafidou, Anastasia; Fudos, Ioannis; Vidal, Franck P. and Tam, Gary K. L. and Roberts, Jonathan C.
Animating a novel character not only needs a lot of effort and time but also requires the intervention of an experienced user. Moreover, the traditional animation pipeline for a set of characters can be a tedious and cumbersome process which often needs to be repeated several times to correct artifacts. We propose a user-friendly, semi-automated efficient method which is realized in two phases: (i) mesh correspondence, and (ii) skeleton and skinning transfer. We have developed a software tool for realizing the entire process without the need of third party software. We have improved the efficiency of the entire animation transfer process. To substantiate this, we provide a comparative performance evaluation with previous competent approaches.
Accelerating Surface Tension Calculation in SPH via Particle Classification and Monte Carlo Integration
(The Eurographics Association, 2019) Zorrilla, Fernando; Sappl, Johannes; Rauch, Wolfgang; Harders, Matthias; Vidal, Franck P. and Tam, Gary K. L. and Roberts, Jonathan C.
Surface tension has a strong influence on the shape of fluid interfaces. We propose a method to calculate the corresponding forces efficiently. In contrast to several previous approaches, we discriminate to this end between surface and non-surface SPH particles. Our method effectively smooths the fluid interface, minimizing its curvature. We make use of an approach inspired by Monte Carlo integration to estimate local normals as well as curvatures, based on which the force can be calculated. The technique is applicable, but not limited to 2D and 3D simulations, and can be coupled with any common SPH formulation. It outperforms prior approaches with regard to total computation time per time step, while being stable and avoiding artifacts.
Sampling with Pinwheel Tiles
(The Eurographics Association, 2019) Ahmed, Abdalla G. M.; Vidal, Franck P. and Tam, Gary K. L. and Roberts, Jonathan C.
We outline an adaptive sampling framework based on Conway's pinwheel tiles. It offers a unique feature that the generated tiles have infinite number of orientation angles, minimizing the strong auto-correlations found on all other lookup-sampling frameworks. We describe a novel string-based approach to enumerate distinct neighbor configurations in pinwheel tiles.
Deep Terrain Expansion: Terrain Texture Synthesis with Deep Learning
(The Eurographics Association, 2019) Toulatzis, Vasilis; Fudos, Ioannis; Vidal, Franck P. and Tam, Gary K. L. and Roberts, Jonathan C.
In real-world applications terrains play a cardinal role in the field of games and geospatial applications such as Geographic Information Systems (GIS). The textures of a terrain are essential for creating virtual photorealistic environments for users. In many cases, the entire texture of a region is not available in high resolution or is much smaller than the required texture to cover a terrain. Tiling of a texture across a terrain or using an enlarged version of it usually fails to provide an acceptable photorealistic result. Consequently, high quality texture synthesis is a central issue in such settings. In this paper, we explore a novel methodology that extends previous work providing both synthesis and expansion/shrinkage of a texture.
Optimising Underwater Environments for Mobile VR
(The Eurographics Association, 2019) Cenydd, Llyr ap; Headleand, Christopher; Vidal, Franck P. and Tam, Gary K. L. and Roberts, Jonathan C.
Mobile Virtual Reality (VR) has advanced considerably in the last few years, driven by advances in smartphone technology. There are now a number of commercial offerings available, from smartphone powered headsets to standalone units with full positional tracking. Similarly best practices in VR have matured quickly, facilitating comfortable and immersive VR experiences. There remains however many optimisation challenges when working with these devices, as while the need to render at high frame rates is universal, the hardware is limited by both computational power and battery capacity. There is also often a requirement that apps run smoothly across a wide variety of headsets. In this paper, we describe lessons learned in rendering and optimising underwater environments for mobile VR, based on our experience developing the popular aquatic safari application 'Ocean Rift'. We start by analyzing essential best practices for mobile app development, before describing low-cost techniques for creating immersive underwater environments. While some techniques discussed are universal to modern mobile VR development, we also consider issues that are unique to underwater applications.
Registration of 3D Triangular Models to 2D X-ray Projections Using Black-box Optimisation and X-ray Simulation
(The Eurographics Association, 2019) Wen, Tianci; Mihail, Radu; Al-maliki, shatha; Letang, Jean; Vidal, Franck; Vidal, Franck P. and Tam, Gary K. L. and Roberts, Jonathan C.
Registration has been studied extensively for the past few decades. In this paper we propose to solve the registration of 3D triangular models onto 2D X-ray projections. Our approach relies extensively on global optimisation methods and fast X-ray simulation on GPU. To evaluate our pipeline, each optimisation is repeated 15 times to gather statistically meaningful results, in particular to assess the reproducibility of the outputs.We demonstrate the validity of our approach on two registration problems: i) 3D kinematic configuration of a 3D hand model, i.e. the recovery of the original hand pose from a postero-anterior (PA) view radiograph. The performance is measured by Mean Absolute Error (MAE). ii) Automatic estimation of the position and rigid transformation of geometric shapes (cube and cylinders) to match an actual metallic sample made of Ti/SiC fibre composite with tungsten (W) cores. In this case the performance is measured in term of F-score (86%), accuracy (95%), precision (75%), recall (100%), and true negative rate (94%). Our registration framework is successful for both test-cases when using a suitable optimisation algorithm.
Evaluating Models for Virtual Forestry Generation and Tree Placement in Games
(The Eurographics Association, 2019) Williams, Benjamin; Ritsos, Panagiotis; Headleand, Christopher; Vidal, Franck P. and Tam, Gary K. L. and Roberts, Jonathan C.
A handful of approaches have been previously proposed to generate procedurally virtual forestry for virtual worlds and computer games, including plant growth models and point distribution methods. However, there has been no evaluation to date which assesses how effective these algorithms are at modelling real-world phenomena. In this paper we tackle this issue by evaluating three algorithms used in the generation of virtual forests - a randomly uniform point distribution method (control), a plant competition model, and an iterative random point distribution technique. Our results show that a plant competition model generated more believable content when viewed from an aerial perspective. We also found that a randomly uniform point distribution method produced forest visualisations which were rated highest in playability and photorealism, when viewed from a first-person perspective. Our results indicate that when it comes to believability, the relationship between viewing perspective and procedural generation algorithm is more important than previously thought.

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