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Item Photorealistic Augmented Reality(Eurographics Association, 2003) Gibson, Simon; Chalmers, AlanAugmenting 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.Item 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-OrWe 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.