Interactive rear-projection displays are important devices in Human-Computer Interaction environments. Providing the experience of working with a familiar tool like a blackboard or smartboard, they expand their possibilities by application-specific features. Unfortunately, in most setups, the interaction is often pen-based and limits the use to a single person.

To overcome these restrictions, we have developed the FlipTouch interactive wall. Based on an IR stereo tracking setup in combination with a DNP HoloScreen, we are able to provide an intuitive interface for collaborative work. Natural interaction is specifically suited for collaboration as people can easily follow the others actions and multiple persons can interact at the same time. This aspect makes hand-gestures ideally suited for direct manipulation on wall-sized displays. The implementation of a gesture-controlled image browser demonstrates one potential area of use. The image browser allows browsing through categories of images and the transformation of multiple images simultaneously using hand gestures.


FlipTouch is an interactive transparent display that can be used in various contexts. Interactivity is based on a stereo tracking setup. Therefore, any application built upon the tracking system receives appropriate data to be further processed. Information from the surface of the screen is interpreted in two ways: Computer vision algorithms extract areas of objects that touch the screen and pass the surrounding bounding rectangles to the application. Moreover, an optical flow field is calculated to extract information about the orientation of objects. Depending on the hardware setup, the tracking can be performed on a separate server (distributed version) or done locally.

Stereo Tracking

We implemented a stereo vision tracking system for the 60” DNP HoloScreen. This screen has special holographic features that enable rear-projection from a specific angle of 35 degrees. Without a projection, the HoloScreen seems transparent as the light from other incident angles than 35 degrees just passes the screen. Tracking user interaction on the HoloScreen is accomplished by a stereo vision setup consisting of two WATEC WAT-502B cameras with manual focus. IR pass filters are applied to the cameras in order to avoid interferences with the projected image. The cameras placed behind the screen capture the whole room, as the HoloScreen is transparent. Excluding the room background is realized by background subtraction. The relevant information is extracted from a combined image of the left and right camera view. Regions of interest appear in a bright contrast.

Image Browser

The image browser application is based on design paradigms for large interactive surfaces. Supported features include the selection of images by category, arranging them in a workspace area, scaling and rotating multiple selected images simultaneously. The basic tracking data is provided by the stereo vision system. The image browser demonstrates a typical application for a collaborative working environment.