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goes beyond the previous camera-based systems; by not using a diffusing projection surface, it permits a high resolution touch image. For example, a high resolution image of a paper document may be captured using a high-resolution still camera, or one of the newer high resolution CMOS video cameras. The absence of a diffuser also permits the cameras to see beyond the display surface, just as they would if placed behind a sheet of glass. This allows a variety of interesting capabilities such as using face recognition techniques to identify the current user, eye to- eye video conferencing, and other processes which are typically the domain of vision-based perceptual user interfaces.

Touch Light physical configuration: DNP

HoloScreen with two IR cameras and IR

Illuminant behind screen.

TOUCHLIGHT的配置-TOUCHLIGHT CONFIGURATION:

The physical configuration of Touch Light is illustrated in Figure. A pair of commonly available Firewire web cameras is mounted behind the display surface such that each camera can see all four corners of the display. The importance of the distance between the cameras is discussed later. The DNP Holo Screen material is applied to the rear surface of the acrylic display surface. The Holo Screen is a special refractive holographic film which scatters light from a rear projector when the incident light is at a particular angle. The material is transparent to all other light, and so is suitable for applications where traditional projection display surfaces would be overwhelmed by ambient light. Typical applications include retail storefronts, where ambient light streaming through windows precludes traditional rear-projection screens.

Additionally the screen is transparent in the near-infrared range. Per manufacturer's instructions the projector is mounted such that the projected light strikes the display at an angle of about 35 degrees. In a typical vertical, eye-level installation, this configuration does not result in the user looking directly into the 'hot spot' of the projector. We note that many projectors are not able to correct for the keystone distortion when the projector is mounted at this extreme angle. In our implementation, we use the NVKeystone digital keystone distortion correction utility that is available on NVidia video cards. Experience with the HoloScreen material suggests that while the light reflected back from the rear of the screen is significantly less than the light scattered out the front, the projected image will still interfere with the image captured by any visible light-based cameras situated behind the display. In the present work we avoid difficulties with visible light reflections by conducting image based sensing in the infrared (IR) domain. An IR illuminant is placed behind the display to illuminate the surface evenly in IR light. Any IR-cut filters in the stock camera are removed, and an IR-pass filter is applied to the lens. If necessary, an IR-cut filter may be applied to the projector. By restricting the projected light to the visible spectrum, and the sensed light to the IR spectrum, the resulting images from the camera do not include artifacts from projected light reflected backwards from the HoloScreen film. In future work we plan to investigate the application of antireflection films applied to the back and also perhaps the front surface of the display to eliminate reflections from the proj