14.3: Illumination Design of a Multi-Touch Sensing Projection Screen for Augmented Virtual Environments

paper presents the illumination engineering for a low-cost multi-touch projection screen. Eight near infrared emitting diode (IRED) strips with optimized line densities serve as the illumination sources for the finger tracking. The design achieves highly uniformed illumination, with an illumination efficiency of 55% and contrast of 0.098. Implementation and experimental results are presented. 1. Introductionreality (AR) differs from virtual reality in the sense that virtual objects are superimposed on a real world scene. It not only enables a user to perceive a cohesively synthesized information space, but also allows the user to naturally interact with the synthesized information using techniques adapted from real-world experiences, promoting a seamless merging of the worlds of atoms and bits (1). Among the many technical challenges persisting in AR, human computer interface (HCI) design is one of the essential component that can affect the wide application of AR systems. Many 3D interface techniques have been explored and examples include motion trackers, joysticks, and datagoves. The interaction techniques using these devices, however, differ quite a bit from the way people naturally interact with the real world and are mostly limited to a single user regime. It is highly desirable to allow a user to directly manipulate a synthesized scene with his or her hands. Recently, Hua proposed to develop a multi-user workbench system integrated with multi-modality 2D and 3D interfaces (2). At the center of the workbench, a rotating table covered with retro- reflective materials can provide stereoscopic multi-views when the user wears a see-through head mounted projection display (HMPD) (3-5). Surrounding the 3D viewing area, eight projectors are tiled together to form a large 2D display area, covering the four sides of the square shaped workbench. Multi-users can share information through both the 2D and 3D displays and may fluently move information between the 2D and 3D displays. One of the essential components of the workbench system is to develop an effective method allowing concurrent user interactions with the 2D and 3D displays without requiring a user to switch between different interface devices. Among the many candidate technologies we evaluated, we conclude that multi-touch sensing, finger tracking, and gesture recognition would provide an excellent interaction support. In this paper, we present the illumination engineering we developed to support multi-touch sensing for the 2D projection display. We firstly set up the design criteria, such as the merit function, and parameters for the illumination optimization. We then discuss choices of near infrared emitting diodes (IREDs) to maximize the merit function as well as to achieve the goal of compactness and low cost. In section 4, we present the illumination optimization based on three parameters: line density distribution of IRED, distance from the IRED strip to the projection screen and the pointing angle of the IRED strip. The optimization results are presented with 55% illumination efficiency and 0.098 contrast. Finally, the experimental implementation and results are presented in section 5.