Chair for Computer Aided Medical Procedures & Augmented Reality
Lehrstuhl für Informatikanwendungen in der Medizin & Augmented Reality

O. Bimber
Projector-based Illumination and Display Techniques
Habilitation TU München, March 2007. (bib)

(Introduction) Rapid advances in electro-mechanics and optics have increased the capabilities of projectors in terms of spatial resolution, brightness, dynamic range, throw-ratio, and speed. Cost reductions, availability, and the fact that projectors (in contrast to flat panels) can display images that are much larger than the devices themselves made them a mass-market product. Besides for (home-)entertainment, education and business purposes, high resolution tiled screens and immersive surround screen projections are used for visualizations of scientific, engineering and other content. Emissive CRT technology is losing more and more ground to light-valve technology, like LCD, LCOS and especially DLP. Compact pocket projectors that are running from battery and communicate to laptops or cell phones via WiFi? will support a maximum level of mobility in future. Besides portable projectors, projection systems will be integrated into next-generation mobile devices, such as cell-phones, PDAs and digital cameras to support built-in flat-panel screens. There is no doubt that LED technology will become bright enough to keep up with today’s projector lamps. Yet one question still remains: What to project on if not carrying around a projection canvas? Other applications do not require mobility and rather benefit from high quality spatial presentations. Examples range from edutainment in museums (such as storytelling projections onto natural stone walls in historical buildings) over architectural applications (such as augmentations of complex illumination or material simulations in real building structures) to video presentations during live stage performances. For all of these cases, real-time image correction techniques are required that enable presentations of visual content on surfaces that are not optimized for projections. Geometric and radiometric distortions, local and global illumination effects, and defocus cause the main visual artifacts that have to be neutralized when approaching a result that comes closer to projections onto conventional (e.g., white planar) screens. Physically, projectors represent point light sources. Their capability of spatially modulating luminance and chrominance on a per-pixel basis, however, allows for computing and creating almost arbitrary shading effects synthetically. In contrast to seeing projectors as mobile or spatial displays, they can be used as controllable light sources for synthesizing a virtual illumination in a real environment. The challenge of a projector-based illumination is to produce a defined lighting situation without the necessary light sources. The only available light sources are the projectors themselves. Consequently, illumination images have to be computed for each projector with the following objectives: First, they must neutralize the physical illumination effects that are caused by each projector as a real point-light source. Second, they have to produce the defined virtual lighting situation synthetically. Applications of projector-based illumination exist in areas, such as physical re-illumination of real artifacts in a computational photography or a live-presentation context, replaying optical holograms with digital light and -potentially- illuminating future television studios. The overall focus of the work that is summarized in this document is on real-time computer graphics methods for computing projection images that produce the desired effects on complex surfaces and optics – either for illumination or for display purposes. Thereby, a broad spectrum of problems and applications is addressed. While section 2 gives a chronological summary of research results and funding sources, section 3 presents details on contributions and differentiations from related work in a more theme oriented way. Finally, section 4 gives an outlook on future directions. The relevant publications are attached to this summary.
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