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    Photorealistic Augmented Reality
    (Eurographics Association, 2003) Gibson, Simon; Chalmers, Alan
    Augmenting real-world images with synthetic objects is becoming of increasing importance in both research and commercial applications, and encompasses aspects of fields such as mobile camera and display technology, computer graphics, image processing, computer vision and human perception. This tutorial presents an in-depth study into the techniques required to produce high fidelity augmented images at interactive rates, and will consider how the realism of the resulting images can be assessed and their fidelity quantified. The first half of the tutorial covers the methods we use to generate augmented images. We will show how commonly available digital cameras can be used to record scene data, and how computer graphics hardware can be used to generate visually realistic augmented images at interactive rates. Specific topics covered will include geometric and radiometric camera calibration, image-based reconstruction of scene geometry and illumination, hardware accelerated rendering of synthetic objects and shadows, and image compositing. The second half of the tutorial discusses in more detail what we are trying to achieve when generating augmented images, and how success can be measured and quantified. Methods for displaying augmented images will be discussed, and techniques for conducting psychophysical experiments to evaluating the visual quality of images will also be covered. Examples of augmented images and video sequences from a real-world interactive interior design application will be shown, and used to illustrate the different ideas and techniques introduced throughout the tutorial.
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    Rapid Shadow Generation in Real-World Lighting Environments
    (The Eurographics Association, 2003) Gibson, Simon; Cook, Jon; Howard, Toby; Hubbold, Roger; Philip Dutre and Frank Suykens and Per H. Christensen and Daniel Cohen-Or
    We propose a new algorithm that uses consumer-level graphics hardware to render shadows cast by synthetic objects and a real lighting environment. This has immediate benefit for interactive Augmented Reality applications, where synthetic objects must be accurately merged with real images. We show how soft shadows cast by direct and indirect illumination sources may be generated and composited into a background image at interactive rates. We describe how the sources of light (and hence shadow) affecting each point in an image can be efficiently encoded using a hierarchical shaft-based subdivision of line-space. This subdivision is then used to determine the sources of light that are occluded by synthetic objects, and we show how the contributions from these sources may be removed from a background image using facilities available on modern graphics hardware. A trade-off may be made at runtime between shadow accuracy and rendering cost, converging towards a result that is subjectively similar to that obtained using ray-tracing based differential rendering algorithms. Examples of the proposed technique are given for a variety of different lighting environments, and the visual fidelity of images generated by our algorithm is compared to both real photographs and synthetic images generated using non-real-time techniques.
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    Flexible Image-Based Photometric Reconstruction using Virtual Light Sources
    (Blackwell Publishers Ltd and the Eurographics Association, 2001) Gibson, Simon; Howard, Toby; Hubbold, Roger
    Photometric reconstruction is the process of estimating the illumination and surface reflectance properties of an environment, given a geometric model of the scene and a set of photographs of its surfaces. For mixed-reality applications, such data is required if synthetic objects are to be correctly illuminated or if synthetic light sources are to be used to re-light the scene. Current methods of estimating such data are limited in the practical situations in which they can be applied, due to the fact that the geometric and radiometric models of the scene which are provided by the user must be complete, and that the position (and in some cases, intensity) of the light sources must also be specified a-priori. In this paper, a novel algorithm is presented which overcomes these constraints, and allows photometric data to be reconstructed in less restricted situations. This is achieved through the use of virtual light sources which mimic the effect of direct illumination from unknown luminaires, and indirect illumination reflected off unknown geometry. The intensity of these virtual light sources and the surface material properties are estimated using an iterative algorithm which attempts to match calculated radiance values to those observed in photographs. Results are presented for both synthetic and real scenes that show the quality of the reconstructed data and its use in off-line mixed-reality applications.