The need to overlay images of the physical desktop and computer ``desktop'' arises only when they are distinct. The DigitalDesk [] shows that this does not have to be the case. In this system, the physical desktop serves also as the electronic desktop. A projector displays electronic documents or windows on the physical desktop, which can be intermixed with physical papers. Users can interact with both by pressing and dragging their fingers, which corresponds to pressing or dragging a pointing device. An overhead camera scans the paper documents and detects finger movements while a microphone attached underneath the desk detects finger presses.
A special application, the DigitalDesk Calculator, shows how this technology is useful for single-user interaction. User can interact with the calculator by either pressing on the projected keys, or more interestingly, pasting numbers directly from a paper to the calculator.
This technology is particularly interesting from a multiuser point of view since one can project the electronic and paper documents on a remote desktop, thereby giving awareness of both objects without the need to overlay the images. A multiuser version of this system has not, however, been built so far. (Can you integrate the TeamWorkstation and DigitalDektop designs?)