Tele- Grafitti

There are several ways of building a remote sketching system. One way is to use a tablet and a stylus to input the sketch and a computer monitor to display the sketch at the remote site. Such systems have a number of disadvantages. Writing with a stylus on a glass tablet is unnatural compared to sketching with a regular pen and paper. Shading and other effects are harder to achieve. Changing color means using the computer to select a new color rather than using a different pen. Incorporating existing hard-copy documents such as a graded exam is impossible.

Figure 1.1: A schematic diagram of a 2 site camera-projector based remote sketching system. The cameras at both sites continuously capture video of what is written on the paper. The video is digitized, compressed, and transmitted to the other site where it is projected onto the paper. Note that the projected video must be warped appropriately to align it correctly with the paper.

Another way of building a remote sketching system is to use a video camera to image the sketch at one end, transmit the video to the other end and displays it there using a projector. See Figure 1.1 for a schematic diagram of such a system. The first such camera-projector based remote sketching system was Pierre Wellner's Xerox "Double Digital Desk" [Wellner, 1993].

Since 1993 systems combining video cameras and projectors have become more and more prevalent. Besides the Xerox "Digital Desk", other such systems include the University of North Carolina's "Office of the Future" [Raskar et al, 1998], INRIA Grenoble's "Magic Board" [Hall et ah, 1999], and Yoichi Sato's "Augmented Desk" [Sato et al., 2000]. A related projector system is Wolfgang Krueger's "Responsive Workbench" [Krueger et ah, 1995], used in Stanford Univer¬sity's "Responsive Workbench" project [Agrawala et al., 1997] and in Georgia Tech's "Perceptive Workbench" [Leibe et al., 2000]. Recently, cameras and projectors have also been combined to develop smart displays...