The Understanding of Meaningful Events in Gesture-Based Interaction - Intelligent Video Event Analysis and Understanding - page 11

Fig. 7 Tap and touch events specify clearly the intent to interact, both from the system as
well as the user's perspective. Top: touch-sensitive mobile devices are becoming more and
more popular and affordable. Bottom: an horizontal interactive surface.
total internal reflection) was introduced by Han [15] and proved to be a simple and
inexpensive technique for enabling multi-touch sensing at high resolution for in-
teractive surfaces. Computer vision allows such creative and flexible solutions and
other approaches have been proposed as well for detecting such touch events. For
example, Wilson's system Touchlight [57] uses image processing techniques in or-
der to combine video frames acquired from two infrared cameras placed behind a
semi-transparent plane facing the user. By combining the distortion-corrected infor-
mation from the two video sources, detection of objects that touch or are in a short
distance of the surface plane is achieved. When the video camera is placed on top
as in the PlayAnywhere system [58], touch events can be detected by comparing the
finger position to its shadow.
Tap and touch events specify where and when interaction takes place allowing
precise segmentation of gesture motions. Tabletop systems stand thus as an easy-to-
use and intuitive technology for interacting with digital content with special tech-
niques and interaction metaphors being proposed [58, 59, 61]. Current applications
include browsing photographs, playing videos, listening to music, viewing map lo-
cations or ordering menus with the great advantage represented by direct manipula-
tion. Besides the detection of standard touch events, investigations have been carried
out in order to support interactions under and above the tabletop [3, 18, 55, 56].