F. Echtler, M. Huber, G. Klinker Shadow Tracking on Multi-Touch Tables AVI '08: 9th International Working Conference on Advanced Visual Interfaces, Naples, Italy, pp. 388-391. (bib)
	Multi-touch interfaces have been a focus of research in recent years, resulting in development of various innovative UI concepts. Support for existing WIMP interfaces, however, should not be overlooked. Although several approaches exist, there is still room for improvement, particularly regarding implementation of the "hover" state, commonly used in mouse-based interfaces. In this paper, we present a multi-touch system which is designed to address this problem. A multi-touch table based on FTIR (frustrated total internal reflection) is extended with a ceiling-mounted light source to create shadows of hands and arms. By tracking these shadows with the rear-mounted camera which is already present in the FTIR setup, users can control multiple cursors without touching the table and trigger a "click" event by tapping the surface with any finger of the corresponding hand. An informal evaluation with 15 subjects found an improvement in accuracy when compared to an unaugmented touch screen.
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