EG UK Theory and Practice of Computer Graphics 2009

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Simulation of X-ray Attenuation on the GPU
(The Eurographics Association, 2009) Vidal, Franck; Garnier, Manuel; Freud, Nicolas; Létang, Jean Michel; John, Nigel W.; Wen Tang and John Collomosse
In this paper, we propose to take advantage of computer graphics hardware to achieve an accelerated simulation of X-ray transmission imaging, and we compare results with a fast and robust software-only implementation. The running times of the GPU and CPU implementations are compared in different test cases. The results show that the GPU implementation with full floating point precision is faster by a factor of about 60 to 65 than the CPU implementation, without any significant loss of accuracy. The increase in performance achieved with GPU calculations opens up new perspectives. Notably, it paves the way for physically-realistic simulation of X-ray imaging in interactive time.
Design and Evaluation of a Hardware Accelerated Ray Tracing Data Structure
(The Eurographics Association, 2009) Steffen, Michael; Zambreno, Joseph; Wen Tang and John Collomosse
The increase in graphics card performance and processor core count has allowed significant performance accel- eration for ray tracing applications. Future graphics architectures are expected to continue increasing the number of processor cores, further improving performance by exploiting data parallelism. However, current ray tracing implementations are based on recursive searches which involve multiple memory reads. Consequently, software implementations are used without any dedicated hardware acceleration. In this paper, we introduce a ray trac- ing method designed around hierarchical space subdivision schemes that reduces memory operations. In addition, parts of this traversal method can be performed in fixed hardware running in parallel with programmable graphics processors. We used a custom performance simulator that uses our traversal method, based on a kd-tree, to compare against a conventional kd-tree. The system memory requirements and system memory reads are analyzed in detail for both acceleration structures. We simulated six benchmark scenes and show a reduction in the number of memory reads of up to 70 percent compared to current recursive methods for scenes with over 100,000 polygons.
Distance Based Feature Detection on 3D Point Sets
(The Eurographics Association, 2009) Ramli, Ahmad; Ivrissimtzis, Ioannis; Wen Tang and John Collomosse
We propose a distance based algorithm for implicit feature detection on 3D point sets. Instead of directly determining whether a point belongs to a feature of the 3D point set or not, we first compute the distance between the point and its nearest feature. The obtained distance function is filtered, removing noise and outliers, and the features of the point set are computed as the zero set of the filtered function. Initial tests show that the proposed method is robust and can deal with amount of noise usually expected in a point set.
Aesthetic-Interaction: Exploring the Importance of the Visual Aesthetic in the Creation of Engaging Photorealistic VR Environments
(The Eurographics Association, 2009) Carroll, Fiona; Wen Tang and John Collomosse
Nearly forty years since its conception, the medium of VR is still an enigma. In many ways, it is a medium that still lacks its own uniform language. VR, and particularly photorealistic VR, is a medium that is so occupied in developing its technological capabilities that its other hidden strengths have been neglected. The research presented in this paper is therefore interested in building a more holistic understanding of the "language" of VR, and aims to look beyond the technological in order to explore the creative and experiential side of VR. The goal of the paper is to cross fertilise the fields of HCI, photorealistic virtual reality and visual aesthetics. In it, the author focuses on the design of an aesthetic-interaction and in doing so, implements a comparative study to explore how the strategic patterning of the aesthetic elements (particularly colour) within the photorealistic VR environment can ensure a more engaging VR experience. In conclusion, the author claims that the next generation design of photorealistic VR experiences should consider a balanced combination of both science and art. It highlights that aesthetics can play as important a role as the development of new and more efficient technologies in getting to the heart of the "engaging" photorealistic VR experience.
Automatically Generating Virtual Humans using Evolutionary Algorithms
(The Eurographics Association, 2009) Albin-Clark, Adrian; Howard, Toby; Wen Tang and John Collomosse
Abstract Virtual Humans are used in many applications either as an embodiment of a real person (an "avatar"), or under the control of a computer program (an "agent" or "non-player character"). The automatic generation of Virtual Humans is a challenging problem if they are to look both plausible and unique within a population. We present an approach which exploits the power of Evolutionary Algorithms (EAs), and provide illustrative examples of how our methods may be realised within the context of surface-based model geometry.
Influencing User Attention Using Real-Time Stylised Rendering
(The Eurographics Association, 2009) Redmond, Niall; Dingliana, John; Wen Tang and John Collomosse
In this paper, we present a series of experiments that were conducted to further understand how using adaptive levels of artistic abstraction within an interactive 3D scene can influence user gaze behaviour. We found that when an object was placed in the center of stylised focus, users took significantly less time to complete a search and recognition task in comparison to normal renderings or when the target object was heavily abstracted i.e. stylistically out-of-focus. We also compared a number of different abstraction techniques and found that some abstraction styles consistently lead to faster search times than others. Finally we performed experiments using an eye-tracker to show that our real-time abstraction techniques can successfully draw user attention to specific objects within an interactive scene. We believe that our experimental framework will be useful in the future for comparing the effectiveness of different non-photorealistic styles in influencing a user's perception of a scene.
Markerless Visual Human Movement Tracking for HCI: What Frequency?
(The Eurographics Association, 2009) Kahlesz, Ferenc; Klein, Reinhard; Wen Tang and John Collomosse
This paper tries to establish a minimal tracking frequency limit for visual human movement tracking algorithms that intend to be useful for the realization of some kind Human-Computer-Interaction (HCI) metaphor. More specifically, we examine the question of this minimal frequency for Augmented/Virtual Reality (AR/VR) navigation and 3D object manipulation. We approach the question from three different perspectives: shortly reviewing non-visual and visual marker-based solutions integrated regularly into AR/VR systems, spectral analysis of human movement and latency implications for AR/VR settings. Finally, we conclude the paper by combining and discussing the results from these different areas. We find that tracking with update rates as low as 12.5Hz can provide a usable basis for interaction. The most important message of the paper is that stable and working (even if slow, when compared to other techniques) markerless tracking algorithms are desperately needed because only working online with and based on such systems can the pros and cons of markerless tracking be evaluated.
Object Interaction Using Tabulated Spheres Subsets
(The Eurographics Association, 2009) Newball, Andres A. Navarro; Wyvill, Geoff; McCane, Brendan; Wen Tang and John Collomosse
Tabulated Sphere Subsets (TSSs) provide a fast way to approximate collision tests between objects whose motion is constrained. A TSS is a subset of a set of spheres that approximate the shape of two objects that might collide. The subset represents only those spheres that can collide under the constrained motion. A TSS is created in three steps: 1) approximating the mesh with spheres; 2) searching the space of possible motion to find which spheres may collide: 3) extracting the spheres required for collision tests and building the table. We applied TSSs to jaw motion and skin/muscle interaction in a model dog and measured the number of spheres generated and the number of calculations needed for collision tests. In these cases TSSs outperforms several standard techniques.
Fast and Accurate Finite Element Method for Deformation Animations
(The Eurographics Association, 2009) Tang, Wen; Wan, Tao Ruan; Niquin, Ceddric; Schildknecht, Alexandre; Wen Tang and John Collomosse
We present a matrix clustering method for speeding up finite element computations for non-rigid object animation. The method increases the efficiency of computing deformation dynamics through a compression scheme that decomposes the large force-displacement matrix into clusters of smaller matrices in order to facilitate the run-time computations of linear finite element based deformations. The deformation results are compared with the results produced by using modal analysis method and the standard linear finite element algorithm. We demonstrate that the proposed method is stable with comparative computational speed to modal analysis method. A hierarchical skeleton-based system is also implemented to add constraints to material nodes. Thus, real-time deformations can be directed by motion captured data sets or key-framed animations.
Facial Expression Transferring with a Deformable Model
(The Eurographics Association, 2009) Xiang, Guofu; Ju, Xiangyang; Holt, Patrik O'B.; Shang, Lin; Wen Tang and John Collomosse
This paper presents an automated approach to transferring facial expressions from a generic facial model onto various individual facial models without requiring any prior correspondences and manual interventions during the transferring process. This approach automatically detects the corresponding feature landmarks between models, and establishes the dense correspondences by means of an elastic energy-based deformable modelling approach. The deformed model, obtained through the deformation process, maintains the same topology as the generic model and the same shape as the individual one. After establishing the dense correspondences, we first transfer the facial expressions onto the deformed model by a deformation transfer technique, and then obtain the final expression models of individual models by interpolating the expression displacements on the deformed model. The results show that our approach is able to produce convincing results on landmark detection, correspondence establishment and expression transferring.
An Edge-based Approach to Adaptively Refining a Mesh for Cloth Deformation
(The Eurographics Association, 2009) Simnett, Timothy J. R.; Laycock, Stephen D.; Day, Andy M.; Wen Tang and John Collomosse
Simulating cloth in real-time is a challenging endeavour due to the number of triangles necessary to depict the potentially frequent changes in curvature, in combination with the physics calculations which model the deformations. To alleviate the costs, adaptive methods are often employed to refine the mesh in areas of high curvature, however, they do not often consider a decimation or coarsening of areas which were refined previously. In addition to this, the triangulation and consistency checks required to maintain a continuous mesh can be prohibitively time consuming when attempting to simulate larger pieces of cloth. In this paper we present an efficient edge-based approach to adaptively refine and coarsen a dynamic mesh, with the aim to exploit the varied nature of cloth by trading the level of detail in flat parts for increased detail in the curved regions of the cloth. An edge-based approach enables fast incremental refinement and coarsening, whereby only two triangles need updating on each split or join of an edge. The criteria for refinement includes curvature, edge length and edge collisions. Simple collision detection is performed allowing interactions between the cloth and the other objects in the environment.
Real-time Rendering of Deformable Translucent Objects
(The Eurographics Association, 2009) Benmounah, Nadir; Jolivet, Vincent; Ghazanfarpour, Djamchid; Wen Tang and John Collomosse
This paper introduces an efficient real-time shading model to simulate light transport in translucent materials. In this work no pre-processing step is needed, allowing us to deform translucent objects at interactive rates. The proposed technique avoids the pre-processing of texture atlas and texture coordinates that may entail distortions and self-occlusion errors. We create a cube map texture atlas on the GPU by a specific projection providing accurate access to neighborhood information is accurate. The texture atlas is generated on-the-fly each time the mesh geometry is modified, allowing us to deform the object geometry in real time keeping valid the subsurface light transport computation.
Interactive Relighting for Stage Use
(The Eurographics Association, 2009) Stephenson, Ian; Wen Tang and John Collomosse
Re-lighting by combining images taken under known lighting conditions to synthesise new lighting configurations is a simple, but powerful technique capable of producing impressive results. However it has found little practical application. Here we demonstrate the integration of a relighting tool into a typical theatrical lighting system, to provide real time previews both offline when the stage is unavailable, and during performance.
An Adaptive Sampling Approach to Incompressible Particle-Based Fluid
(The Eurographics Association, 2009) Hong, Woosuck; House, Donald H.; Keyser, John; Wen Tang and John Collomosse
We describe an adaptive particle-based technique for simulating incompressible fluid that uses an octree structure to compute inter-particle interactions and to compute the pressure field. Our method extends the hybrid Flip technique by supporting adaptive splitting and merging of fluid particles, and adaptive spatial sampling for the reconstruction of the velocity and pressure fields. Particle splitting allows a detailed sampling of fluid momentum in regions of complex flow. Particle merging, in regions of smooth flow, reduces memory and computational overhead. The octree supporting field-based calculations is adapted to provide a fine spatial reconstruction where particles are small and a coarse reconstruction where particles are large. This scheme places computational resources where they are most needed, to handle both flow and surface complexity. Thus, incompressibility can be enforced even in very small, but highly turbulent areas. Simultaneously, the level of detail is very high in these areas, allowing the direct support of tiny splashes and small-scale surface tension effects. This produces a finely detailed and realistic representation of surface motion.
Discrete Element Modelling Using a Parallelised Physics Engine
(The Eurographics Association, 2009) Longshaw, Stephen M.; Turner, Martin J.; Finch, Emma; Gawthorpe, Robert; Wen Tang and John Collomosse
Discrete Element Modelling (DEM) is a technique used widely throughout science and engineering. It offers a convenient method with which to numerically simulate a system prone to developing discontinuities within its structure. Often the technique gets overlooked as designing and implementing a model on a scale large enough to be worthwhile can be both time consuming and require specialist programming skills. Currently there are a few notable efforts to produce homogenised software to allow researchers to quickly design and run DEMs with in excess of 1 million elements. However, these applications, while open source, are still complex in nature and require significant input from their original publishers in order for them to include new features as a researcher needs them. Recently software libraries notably from the computer gaming and graphics industries, known as physics engines, have emerged. These are designed specifically to calculate the physical movement and interaction of a system of independent rigid bodies. They provide conceptual equivalents of real world constructions with which an approximation of a realistic scenario can be quickly built. This paper presents a method to utilise the most notable of these engines, NVIDIAs PhysX, to produce a parallelised geological DEM capable of supporting in excess of a million elements.
A Framework for Physically Based Forest Fire Animation
(The Eurographics Association, 2009) Gundersen, Odd Erik; Skjermo, Jo; Wen Tang and John Collomosse
Abstract In this paper, we propose a conceptual framework for animating physically based forest fires. Animating forest fire is a computationally demanding task as trees are intricate structures and fire is a highly complex process. The framework is divided into three conceptual levels, which are a large scale forest fire simulation, a small scale tree fire simulation, and an intermediate level connecting the two. Problems with and possible solutions to all three levels are discussed. Based on this discussion, a complete framework is proposed.
Visual Representation of Multiple Associations in Data using Constrained Graph Layout
(The Eurographics Association, 2009) Xu, Weijia; Sreevalsan-Nair, Jaya; Wen Tang and John Collomosse
This paper presents a new approach for simultaneously visualizing multiple exclusive associations, defined on the same dataset, using constrained graph layout. We work with two different associations at a time, which can be represented as a binary graph operation. Given an initial graph layout which represents an association of the data, another set of constraints is applied to the graph to represent a second association on the same dataset to obtain the final layout. Our motivation is to preserve some features of the first layout as well as to achieve a simultaneous view of both the associations. We use this approach generically for three applications: for visualization of data with geometric and categorical constraints, respectively. We further propose to extend it to multiple associations, by using the binary operation multiple times.
Texture Classification using Fractal Geometry for the Diagnosis of Skin Cancers
(The Eurographics Association, 2009) Blackledge, J. M.; Dubovitskiy, D. A.; Wen Tang and John Collomosse
We present an approach to object detection and recognition in a digital image using a classification method that is based on the application of a set of features that include fractal parameters such as the Lacunarity and Fractal Dimension. The principal issues associated with object recognition are presented and a self-learning procedure for designing a decision making engine using fuzzy logic and membership function theory considered. The methods discussed, and the 'system' developed, have a range of applications in 'machine vision' and in this publication, we focus on the development and implementation of a skin cancer screening system that can be used in a general practice by non-experts to 'filter' normal from abnormal cases so that in the latter case, a patient can be referred to a specialist. The paper provides an overview of the system design and includes a link from which interested readers can download and use a demonstration version of the system developed to date.
An Aliasing Theory of Shadow Mapping
(The Eurographics Association, 2009) Zhang, Fan; Zhao, Chong; Sun, Hanqiu; Wen Tang and John Collomosse
Shadow mapping is a popular image-based technique for real-time shadow rendering. Although numerous improvements have been made to help anti-aliasing in shadow mapping, there is a lack of mathematical tools that allow us to quantitatively analyze aliasing errors in its variants. In this paper, we establish an aliasing theory to achieve this goal. A generalized representation of aliasing errors is derived from a pure mathematical point of view. The major highlight of this representation is the ability of quantifying the aliasing error at any position for general view-light configurations. On the contrary, due to the geometric assumptions used in the computational model, previous work analyzes the aliasing only along the view direction in the simplest case where the light and view directions are orthogonal. Subsequently, as a direct application of our theory, we present a comparison of aliasing distributions in a few representative variants of perspective shadow maps. We believe that these theoretical results are useful to better understand shadow mapping, and thus inspire people to develop novel techniques in this area.
Calibrating a COTS Monitor to DICOM Standard
(The Eurographics Association, 2009) Grimstead, Ian J.; Avis, Nick J.; Wen Tang and John Collomosse
Abstract We present a method for calibrating a commodity, off-the-shelf (COTS) monitor (costing in the region of £200) to produce a greyscale image approximately calibrated to the DICOM standard, rather than require a 10-bit radiology monitor (costing in the region of £10,000). We use the concept of PseudoGrey to extend the available shades of grey from 256 to 5,800, which is in excess of a 12-bit greyscale. The chromaticity of the resulting greyscale is analysed to verify that the colour introduced does not unduly detract from a pure greyscale image. The behaviour of low intensity levels in the COTS monitor is also analysed, showing that a naive approach to estimating luminance from individual passes through the red, green and blue components is insufficient to produce an accurate intensity range. The results show that we can achieve a basic DICOM calibration (with FIT and LUM tests), but we have yet to test for further variability (such as off-axis deterioration in brightness or inconsistent luminance across a display). As well as displaying medical images, this approach may be of use in other areas requiring a high dynamic range, such as thermal imagery or images taken through multiple alternative exposures.

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