Vision Based Hand Gesture Interfaces for Wearable Computing and ...

Chapter 4. HandVu: A Computer Vision System for Hand Interfaces
Hand Detection
The initial stage of the vision system attempts detection of the hand in a
particular posture. Since hands are frequently over-exposed in comparison to
the background, the vision system performs automatic exposure correction for a
smaller area than the entire image (see Section 4.2.2). To facilitate this, the hand
is only detected in a rectangular region that can be specified by the interface
designer. For our applications, we chose the central part of the comfort zone as
discussed in Chapter 3 to function as the hand detection area. If the detection
was not successful, vision processing for the current frame ends here. If the hand
was detected, the location of a 2D bounding box is sent to the tracking initializa-
tion stage. More information on how the detection is facilitated can be found in
Chapter 5.
Tracking initialization
The observed hand color is then learned in a color histogram, given the bound-
ing box location and a probability map that specifies the likelihood of pixels within
that area to belong to the hand. This color is contrasted to a reference area of
background image areas. Next, a “Flock of Features” is placed on what is believed
to be the hand. (See Chapter 6 for tracking details.) No further processing is done
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