Piotr Dubla

High-dynamic-range video solution

The natural world presents our visual system with a wide, ever-changing range of colors and intensities. Existing video cameras are only capable of capturing a limited part of this wide range with sufficient resolution. High-dynamic-range (HDR) images can represent most of the real worlds luminances, but until now capturing HDR images with a linear-response function has been limited to static scenes. This demonstration showcases a novel complete HDR video solution. The system includes a unique HDR video camera capable of capturing a full HDTV video stream consisting of 20 f-stops dynamic range at a resolution of 1920 x 1080 pixels at 30 frames per second; an encoding method for coping with the huge amount of data generated by the camera (achieving a compression ratio of up to 100:1 and real-time decompression); and a new 22-inch desktop HDR display for directly visualizing the dynamic HDR content.

Virtual relighting of a Roman statue head from Herculaneum: a case study

High-fidelity computer graphics offer the possibility for archaeologists to put excavated cultural heritage artefacts virtually back into their original setting and illumination conditions. This enables hypotheses about the perception of objects and their environments to be investigated in a safe and controlled manner. This paper presents a case study of the pipeline for the acquisition, modelling, rapid prototyping and virtual relighting of a Roman statue head preserved at Herculaneum in Italy. The statue head was excavated in 2006, after having been buried during the eruption of Mount Vesuvius in AD79.

Investigation of the beat rate effect on frame rate for animated content

Knowledge of the Human Visual System (HVS) may be exploited in computer graphics to significantly reduce rendering times without the viewer being aware of any resultant image quality difference. Furthermore, cross-modal effects, that is the influence of one sensory input on another, for example sound and visuals, have also recently been shown to have a substantial impact on viewer perception of image quality. In this paper we investigate the relationship between audio beat rate and video frame rate in order to manipulate temporal visual perception. This represents an initial step towards establishing a comprehensive understanding for the audio-visual integration in multisensory environments.

The virtual reconstruction and daylight illumination of the Panagia Angeloktisti

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.

Wait-free shared-memory irradiance cache

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 structures, 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.

Instant Caching for Interactive Global Illumination

The ability to interactively render dynamic scenes with global illumination is one of the main challenges in computer graphics. The improvement in performance of interactive ray tracing brought about by significant advances in hardware and careful exploitation of coherence has rendered the potential of interactive global illumination a reality. However, the simulation of complex light transport phenomena, such as diffuse interreflections, is still quite costly to compute in real time. In this paper we present a caching scheme, termed Instant Caching, based on a combination of irradiance caching and instant radiosity. By reutilising calculations from neighbouring computations this results in a speedup over previous instant radiosity‐based approaches. Additionally, temporal coherence is exploited by identifying which computations have been invalidated due to geometric transformations and updating only those paths. The exploitation of spatial and temporal coherence allows us to achieve superior frame rates for interactive global illumination within dynamic scenes, without any precomputation or quality loss when compared to previous methods; handling of lighting and material changes are also demonstrated.

A physically-based client-server rendering solution for mobile devices

Mobile devices, also known as small-form-factor (SFF) devices such as mobile phones, PDAs and ultra mobile PCs have continued to grow in popularity. Improvements in SFF hardware has enabled a range of suitable applications such as gaming, interactive visualisation and mobile mapping. Although high-fidelity graphic systems typically have significant computational requirements, the time taken may be largely resolution dependent. The limited resolution of SFFs indicates such platforms are prime candidates for running high-fidelity graphics. Due to the limited hardware available on mobile devices, it is not currently possible to produce high-fidelity graphics in reasonable time. However, most SFFs have some degree of network capability. Using a remote server in conjunction with a mobile device to render high-fidelity graphics on demand allows us to substantially reduce the total rendering time. This paper introduces a client-server framework for minimising rendering times using a cost function to predict optimal distribution of rendering.

Time-constrained high-fidelity rendering on local desktop grids

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.

Adaptive Interleaved Sampling for Interactive High-Fidelity Rendering

Recent advances have made interactive ray tracing (IRT) possible on consumer desktop machines. These advances have brought about the potential for interactive global illumination (IGI) with enhanced realism through physically based lighting. IGI, unlike IRT, has a much higher computational complexity. Furthermore, since non‐primary rays constitute the majority of the computation, the rays are predominantly incoherent, making impractical many of the methods that have made IRT possible. Two methods that have already shown promise in decreasing the computational time of the GI solution are interleaved sampling and adaptive rendering. Interleaved sampling is a generalized sampling scheme that smoothly blends between regular and irregular sampling while maintaining coherence. Adaptive rendering algorithms adjust rendering quality, non‐uniformally, using a guidance scheme. While adaptive rendering has shown to provide speed‐up when used for off‐line rendering it has not been utilized in IRT due to its naturally incoherent nature. In this paper, we combine adaptive rendering and interleaved sampling within a component‐based solution into a new approach we term adaptive interleaved sampling. This allows us to tailor new adaptive heuristics for interleaved sampling of the individual components of the GI solution significantly improving overall performance. We present a novel component‐based IGI framework for which we achieve interactive frame rates for a range of effects such as indirect diffuse lighting, soft shadows and single scatter homogeneous participating media.

Parallel path tracing using incoherent path-atom binning

Current parallel graphics algorithms minimise memory access latency by tracing packets of coherent rays. This coherency, however, breaks down after several bounces, and is unsuited to acceleration techniques such as selective rendering. This paper presents an unbiased path tracing algorithm which is insensitive to the coherency of the rays traced, allowing it to run on diverse architectures including massively SIMD processors. Bins of path-atoms are created and processed to form a path tracing circular buffer. Latency is hidden by n-buffering the load/save operations between bins. We demonstrate our approach as an implementation on the massively parallel SIMD architecture, the ClearSpeed CSX600.