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hat it lies at an arbitrary depth above the display. Furthermore, multiple such planes at various depths may be defined depending on the application. Such an arrangement may be used to implement 'hover', as used in pen-based models of interaction. The image rectification and image comparison processes do not require the physical presence of the display. In fact, it is possible to configure TouchLight to operate without the HoloScreen, in which case the 'touch' interaction is performed on an invisible plane in front of the user. In this case, it may be unnecessary to perform imaging in IR.

Image Normalization:

A further image normalization step may be performed to remove effects due to the non- uniformity of the illumination. The current touch image may be normalized pixel-wise by

Where minimum and maximum images min I and max I may be collected by a calibration phase in which the user moves a white piece of paper over the display surface. This normalization step maps the white page to the highest allowable pixel value, corrects for the non-uniformity of the illumination, and also captures any fixed noise patterns due to IR sources and reflections in the environment. After normalization, other image processing algorithms which are sensitive to absolute gray level values may proceed. For example, binarization and subsequent connected components algorithm, template matching and other computer vision tasks rely on uniform illumination.

Touch Image Interpretation:

Figure 5 shows three different visualizations of the touch image as it is projected back to the user. Figure 5a shows the user's hand on the surface, which displays both left and right undistorted views composted together (not a simple reflection of two people in front of the display). This shows how an object fuses as it gets closer to the display. Figure 5b shows a hand on the surface, which displays the computed touch image. Note that because of the computed homography, the image of the hand indicated by bright regions is physically aligned with the hand on the screen. Presently we have only begun exploring the possibilities in interpreting the touch image. Figure 5c shows an interactive drawing program that adds strokes derived from the touch image to a drawing image while using a cycling color map.

应用-APPLICATIONS:

Visible Light Surface Scanning

Video Conferencing

Minority Report Interfaces

Augmented Reality and Spatial Displays

总结-CONCLUSION:

A novel interactive surface and touch screen technology is presented. TouchLight uses two cameras in combination with a commercially available projection screen technology which allows projection onto an otherwise transparent surface. This arrangement allows for certain novel applications and flexibility which go beyond previous related technologies. We have presented image processing techniques to produce a touch image useful for many gesture-based and perceptual computing scenarios. A number of applications which take advantage of the unique characteristics of TouchLight have been suggested; we hope to explore some of these in the future.