Selected Readings in Vision and Graphics
edited by Luc Van Gool, Gábor Székely, Markus Gross, Bernt Schiele

Volume 26

Christian Spagno
Immersive VR Projection System with
Simultaneous Image Acquisition
using Active Projection Screens

First edition 2003, 198 pages, 64,00. ISBN 3-89649-888-6

This thesis covers the hardware component of a novel collaborative, immersive virtual environment system, namely the spatially immersive projection system and the image acquisition system. The main challenge associated with the hardware was to combine the projection with the image acquisition. In order to meet this challenge, electrically switchable "phase dispersed liquid crystal (PDLC)" glass panels are used as projection walls. The panels are switched to transparent for acquisition and opaque for projection. The switching is repeated 62.5 times per second. The cameras, which are located outside of the projection room, can acquire an image of the user through the PDLC glass panels during the transparent states.
The switchable projection screens are discussed in this dissertation. The properties of the PDLC glass panels are analyzed, including the electrical and the projection properties. The triggering signals, which drive the glass panels, are optimized to minimize the switching times.
An active LCD stereo projection system was developed to enable stereo projection in conjunction with image acquisition. A bright illumination with a homogenous light distribution is necessary to facilitate the silhouette extraction and the texture acquisition. On the other hand, a dark surrounding is advantageous for a good immersion. Therefore an active illumination consisting of 9,984 LEDs is used, which is switched on and off 62.5 times per second. The illumination is only on during image acquisition. Modified shutter glasses are used to keep the light away from the user. This is achieved by blocking both shutters of the glasses during image acquisition.

Christian Spagno is Research Associate at the Center of Product Development of the Swiss Federal Institute of Technology (ETH) Zurich. He received an MSc degree in Electrical Engineering (Dipl. El.-Ing. ETH) from the ETH Zurich in 1999. His research interests include virtual reality systems, projection technologies, power electronics and product development processes.

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