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Now showing 1 - 7 of 7
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    Recreating Early Islamic Glass Lamp Lighting
    (The Eurographics Association, 2009) Jr., Joseph T. Kider; Fletcher, Rebecca L.; Yu, Nancy; Holod, Renata; Chalmers, Alan; Badler, Norman I.; Kurt Debattista and Cinzia Perlingieri and Denis Pitzalis and Sandro Spina
    Early Islamic light sources are not simple, static, uniform points, and the fixtures themselves are often combinations of glass, water, fuel and flame. Various physically based renderers such as Radiance are widely used for modeling ancient architectural scenes; however they rarely capture the true ambiance of the environment due to subtle lighting effects. Specifically, these renderers often fail to correctly model complex caustics produced by glass fixtures, water level, and fuel sources.While the original fixtures of the 8th through 10th century Mosque of Cordoba in Spain have not survived, we have applied information gathered from earlier and contemporary sites and artifacts, including those from Byzantium, to assume that it was illuminated by either single jar lamps or supported by polycandela that cast unique downward caustic lighting patterns which helped individuals to navigate and to read. To re-synthesize such lighting, we gathered experimental archaeological data and investigated and validated how various water levels and glass fixture shapes, likely used during early Islamic times, changed the overall light patterns and downward caustics. In this paper, we propose a technique called Caustic Cones, a novel data-driven method to "shape" the light emanating from the lamps to better recreate the downward lighting without resorting to computationally expensive photon mapping renderers.Additionally, we demonstrate on a rendering of the Mosque of Cordoba how our approach greatly benefits archaeologists and architectural historians by providing a more authentic visual simulation of early Islamic glass lamp lighting.
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    High Dynamic Range Imaging and Low Dynamic Range Expansion for Generating HDR Content
    (The Eurographics Association, 2009) Banterle, Francesco; Debattista, Kurt; Artusi, Alessandro; Pattanaik, Sumanta; Myszkowski, Karol; Ledda, Patrick; Bloj, Marina; Chalmers, Alan; M. Pauly and G. Greiner
    In the last few years, researchers in the field of High Dynamic Range (HDR) Imaging have focused on providing tools for expanding Low Dynamic Range (LDR) content for the generation of HDR images due to the growing popularity of HDR in applications, such as photography and rendering via Image-Based Lighting, and the imminent arrival of HDR displays to the consumer market. LDR content expansion is required due to the lack of fast and reliable consumer level HDR capture for still images and videos. Furthermore, LDR content expansion, will allow the re-use of legacy LDR stills, videos and LDR applications created, over the last century and more, to be widely available. The use of certain LDR expansion methods, those that are based on the inversion of tone mapping operators, has made it possible to create novel compression algorithms that tackle the problem of the size of HDR content storage, which remains one of the major obstacles to be overcome for the adoption of HDR. These methods are used in conjunction with traditional LDR compression methods and can evolve accordingly. The goal of this report is to provide a comprehensive overview on HDR Imaging, and an in depth review on these emerging topics.
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    A Psychophysical Evaluation of Inverse Tone Mapping Techniques
    (The Eurographics Association and Blackwell Publishing Ltd, 2009) Banterle, Francesco; Ledda, Patrick; Debattista, Kurt; Bloj, Marina; Artusi, Alessandro; Chalmers, Alan
    In recent years inverse tone mapping techniques have been proposed for enhancing low-dynamic range (LDR) content for a high-dynamic range (HDR) experience on HDR displays, and for image based lighting. In this paper, we present a psychophysical study to evaluate the performance of inverse (reverse) tone mapping algorithms. Some of these techniques are computationally expensive because they need to resolve quantization problems that can occur when expanding an LDR image. Even if they can be implemented efficiently on hardware, the computational cost can still be high. An alternative is to utilize less complex operators; although these may suffer in terms of accuracy. Our study investigates, firstly, if a high level of complexity is needed for inverse tone mapping and, secondly, if a correlation exists between image content and quality. Two main applications have been considered: visualization on an HDR monitor and image-based lighting.
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    The Virtual Reconstruction and Daylight Illumination of the Panagia Angeloktisti
    (The Eurographics Association, 2009) Happa, Jassim; Artusi, Alessandro; Dubla, Piotr; Bashford-Rogers, Tom; Debattista, Kurt; Hulusic, Vedad; Chalmers, Alan; Kurt Debattista and Cinzia Perlingieri and Denis Pitzalis and Sandro Spina
    High-fidelity virtual reconstructions can be used as accurate 3D representations of historical environments. After modelling the site to high precision, physically-based and historically correct light models must be implemented to complete an authentic visualisation. Sunlight has a major visual impact on a site; from directly lit areas to sections in deep shadow. The scene illumination also changes substantially at different times of the day. In this paper we present a virtual reconstruction of the Panagia Angeloktisti; a Byzantine church on Cyprus. We investigate lighting simulations of the church at different times of the day, making use of Image-Based Lighting, using High Dynamic Range Environment Maps of photographs and interpolated spectrophotometer data collected on site. Furthermore, the paper also explores the benefits and disadvantages of employing unbiased rendering methods such as Path Tracing and Metropolis Light Transport for cultural heritage applications.
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    High Dynamic Range Imaging and Low Dynamic Range Expansion for Generating HDR Content
    (The Eurographics Association and Blackwell Publishing Ltd, 2009) Banterle, Francesco; Debattista, Kurt; Artusi, Alessandro; Pattanaik, Sumanta; Myszkowski, Karol; Ledda, Patrick; Chalmers, Alan
    In the last few years, researchers in the field of High Dynamic Range (HDR) Imaging have focused on providing tools for expanding Low Dynamic Range (LDR) content for the generation of HDR images due to the growing popularity of HDR in applications, such as photography and rendering via Image-Based Lighting, and the imminent arrival of HDR displays to the consumer market. LDR content expansion is required due to the lack of fast and reliable consumer level HDR capture for still images and videos. Furthermore, LDR content expansion, will allow the re-use of legacy LDR stills, videos and LDR applications created, over the last century and more, to be widely available. The use of certain LDR expansion methods, those that are based on the inversion of Tone Mapping Operators (TMOs), has made it possible to create novel compression algorithms that tackle the problem of the size of HDR content storage, which remains one of the major obstacles to be overcome for the adoption of HDR. These methods are used in conjunction with traditional LDR compression methods and can evolve accordingly. The goal of this report is to provide a comprehensive overview on HDR Imaging, and an in depth review on these emerging topics.
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    Wait-Free Shared-Memory Irradiance Cache
    (The Eurographics Association, 2009) Dubla, Piotr; Debattista, Kurt; Santos, Luis Paulo; Chalmers, Alan; Kurt Debattista and Daniel Weiskopf and Joao Comba
    The irradiance cache (IC) is an acceleration data structure which caches indirect diffuse irradiance values within the context of a ray tracing algorithm. In multi-threaded shared memory parallel systems the IC must be shared among rendering threads in order to achieve high efficiency levels. Since all threads read and write from it an access control mechanism is required, which ensures that the data structure is not corrupted. Besides assuring correct accesses to the IC this access mechanism must incur minimal overheads such that performance is not compromised. In this paper we propose a new wait-free access mechanism to the shared irradiance cache. Wait-free data struc- tures, unlike traditional access control mechanisms, do not make use of any blocking or busy waiting, avoiding most serialisation and reducing contention. We compare this technique with two other classical approaches: a lock based mechanism and a local write technique, where each thread maintains its own cache of locally evaluated irradiance values. We demonstrate that the wait-free approach significantly reduces synchronisation overheads compared to the two other approaches and that it increases data sharing over the local copy technique. This is, to the extent of our knowledge, the first work explicitly addressing access to a shared IC; this problem is becoming more and more relevant with the advent of multicore systems and the ever increasing number of processors within these systems.
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    Time-constrained High-fidelity Rendering on Local Desktop Grids
    (The Eurographics Association, 2009) Aggarwal, Vibhor; Debattista, Kurt; Dubla, Piotr; Bashford-Rogers, Thomas; Chalmers, Alan; Kurt Debattista and Daniel Weiskopf and Joao Comba
    Parallel computing has been frequently used for reducing the rendering time of high-fidelity images, since the generation of such images has a high computational cost. Numerous algorithms have been proposed for parallel rendering but they primarily focus on utilising shared memory machines or dedicated distributed clusters. A local desktop grid, composed of arbitrary computational resources connected to a network such as those in a lab or an enterprise, provides an inexpensive alternative to dedicated clusters. The computational power offered by such a desktop grid is time-variant as the resources are not dedicated. This paper presents fault-tolerant algorithms for rendering high-fidelity images on a desktop grid within a given time-constraint. Due to the dynamic nature of resources, the task assignment does not rely on subdividing the image into tiles. Instead, a progressive approach is used that encompasses aspects of the entire image for each task and ensures that the time-constraints are met. Traditional reconstruction techniques are used to calculate the missing data. This approach is designed to avoid redundancy to maintain time-constraints. As a further enhancement, the algorithm decomposes the computation into components representing different tasks to achieve better visual quality considering the time-constraint and variable resources. This paper illustrates how the component-based approach maintains a better visual fidelity considering a given time-constraint while making use of volatile computational resources.