The Department of Computer Science at the University of Cyprus cordially invites you to the PhD Defense entitled:

Real-Time High Quality HDR Illumination and Tonemapped Rendering

Speaker: Despina Michael
Affiliation: University of Cyprus, Cyprus
Category: PhD Defense
Location: Room 147, Faculty of Pure and Applied Sciences (FST-01), 1 University Avenue, 2109 Nicosia, Cyprus (directions)
Date: Thursday, July 15th, 2010
Time: 9:00-10:00 EET
Host: Yiorgos Chrysanthou (yiorgos AT

Real-time realistic rendering of a computer generated scene is one of the core research areas in computer graphics as it is required in several applications such as computer games, training simulators, medical and architectural packages and many other fields. The key factor of realism in the rendered images is the simulation of light transport based on the given lighting conditions. More natural results are achieved by using luminance values near to the physical ones. However, the vast range of real luminance values has a far greater range of values than what can be displayed on standard monitors. As a final step to the rendering process a Tonemapping operator needs to be applied in order to transform the values in the rendered image to displayable values. A full rendering pipeline that integrates illumination and tonemapping, giving high quality results in real-time frame rate is useful to exist. Such a rendering pipeline would be used in interactive applications which require a high degree of realism. Illumination of a scene is usually approximated with the rendering equation. Current illumination algorithms, in order to achieve high frame rates, compromises the quality with assumptions for several factors that rendering equation depends on, or assuming static scenes so they can exploit precomputations. Such precomputations usually have huge amount of memory requirements. The computational cost increases more, with the increase in the number of light sources and the number of vertices of the objects in the scene. In this thesis we propose an illumination algorithm for dynamic scenes which its run-time performance is not affected by these parameters and has only moderate memory requirements. In this way we can have high frame rates without compromising the quality. The key idea of our algorithm is the pre-integration of contribution of all light sources in a single 3D vector, in such a way that this value is valid for any possible receiver. At run-time this value is used to compute the radiance at each point of the scene based on its known orientation. Recent illumination algorithms, including ours, use environment maps to represent the incident lighting in the scene. Environment maps enable natural environment lighting conditions to be used, thus increasing the realism of the obtained result. Environment maps usually have high dynamic range (HDR) values allowing representation of luminances closer to the natural ones as compared to standard low dynamic range (LDR) images. When HDR environment maps are used, the whole rendering process is done in HDR space, giving an HDR image as output. Typically this needs to be tonemapped into LDR values that can be displayed on standard monitors. There are two categories of tonemapping algorithms: local tonemapping operators produce high quality LDR images in low frame rates, while global tonemapping operators produce moderate quality results in high frame rates. Neither of these categories is suitable in our case where we need to use tonemapping for real-time realistic results. In this thesis, we propose a new framework: selective tonemapping which addresses both requirements. The key idea of this framework is to apply the expensive computations of Tonemapping only to the areas of images which are perceptually important. Selective tonemapping combines the advantages of both categories of current tonemapping algorithms. A full rendering system has been developed which integrates HDR illumination computation and the selective tonemapping framework. Results show high quality images at real-time frame rates. Moreover, it is demonstrated that the application of tonemapping makes illumination algorithms more tolerant to visual perceptual errors.

Short Bio:
Despina Michael is a PhD Candidate at the Department of Computer Science, University of Cyprus.

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