Survey of Pen-and-Paper Computing - Human-Computer Interaction - page 55

collaborative view. A second tagging technique uses separate paper cards containing
an inventory of tagging categories that can be modified and extended by end-users.
Handwritten Referencing
Handwritten annotations often contain references to different passages of the same
document or to a second documents. Such user-defined references are not only ben-
eficial for quick retrieval of information but also help in integrating and structuring
information from many sources. We will now review pen-and-paper systems that
provide for creating and following hyperlinks on paper.
PaperLink [5] was an early system within this class. It uses a specific pen onto
which a camera is attached (Fig. 2.19 shows a commercialized version of Paper-
Link). This camera serves for creating and detecting link hot-spots. The visual con-
tents of the document serve as link anchors. If the pen is placed on a paper document,
the camera captures an image of the document area around the pen tip. The image
is processed on a computer using simple computer vision techniques. The pattern
which appears at the center of the image (typically an individual word) is extracted.
This pattern can be associated with a digital resource and serves from now on as a
link hot-spot. If it is detected in the camera image, the target resource is opened on
the computer.
The Interactive Multimedia Textbook [68] offers similar pen-based interactions
for creating and following hyperlinks from printed documents to Web pages. It relies
on an ultrasonic pen. Therefore link anchors do not have to be bound to specific
Fig. 2.19 The Hitachi LinkStick is a commercialized version of PaperLink. The pen has a built-
in camera. From the camera image, a text pattern is extracted and acts as anchor for a hyperlink
(photo courtesy of Toshifumi Arai)