The Understanding of Meaningful Events in Gesture-Based Interaction - Intelligent Video Event Analysis and Understanding - page 7

regions of interest around it. The preferred choice in this case would be to detect
the operator's face as robust solutions such as the Viola and Jones face detector do
exist for accomplishing this task [52]. Once the location of the operator face and,
implicitly, the location of his head are known, the positions of other body parts
are inferred using simple geometry constraints. Figure 4 illustrates this idea with
several regions dynamically computed around the user's head at one arm-length
around his body. Even more, detecting the face brings in another advantage: as the
face region will expose skin-colored pixels, on-the-fly calibration of color detectors
can be performed [7] which increases system robustness and adaptability to the
environment.
Fig. 4 The user's face can be robustly detected and used subsequently for inferring the loca-
tions of other body parts. Following [7] and [32], special regions of interest may be defined
around the bounding rectangle of the user's face. When the hand is detected in one particular
region an event will be triggered signaling the start, continuation or ending of a gesture. A
wave gesture can be described for example as a series of 1-2-1-2-1 location events.
Cerlinca et al. [7] define and use such regions of interest around the human body in
order to facilitate segmentation and recognition of free hand gestures. Their purpose
is to transmit commands to a mobile robot that may circulate in any environment.
Ten such regions are defined around the operator's face which is reliably detected
using the Viola and Jones classifier. Skin color-based thresholding is further applied
to these regions only in order to detect the operator's hands. Combinations of several
active regions (for which hands were detected inside) correspond to various gesture
commands such as move forward, backward, turn left, turn right, etc.
Marcel [32] performs a similar partitioning of the space around the user's face
combined with anthropometry constraints in order to detect the location of the hand.
The scenario is very similar to the one illustrated in Figure 4. The user's intention for
producing a gesture is detected by monitoring the active windows that are formed in
the body-face space. When skin-colored objects are detected within these predefined
windows, assumption of the user hand is taken and a posture recognizer further
employed.
Iannizzotto et al. [19] use the same principle of location-based events for de-
tecting when a gesture command starts. The authors' Graylevel VisualGlove system
does not track the whole hand but rather the thumb and index fingers only in order to
simulate mouse operations. When both fingers are detected inside a predefined area