Learning OpenCV, 2nd Edition

reason to expect much spatial correlation in this noise and so its signal is characterized by a large number

of very small regions.

Figure 9-6: Frame differencing: a tree is waving in the background in the current (upper-left) and previous

(upper-right) frame images; the difference image (lower-left) is completely cleaned up (lower-right) by the

connected-components method

pruning at this size threshold. We will see

(

Figure 9-7) that it does so nicely.

Now consider the situation in which a foreground object (our ubiquitous hand) passes through the view of

the imager.

X

Figure 9-7

X shows two frames that are similar to those in

X

Figure 9-6X except that now there is a hand moving across from left to right. As before, the current frame

(upper-left) and the previous frame (upper-right) are shown along with the response to frame differencing

(lower-left) and the fairly good results of the connected-component cleanup (lower-right).

Figure 9-7: Frame difference method of detecting a hand, which is moving left to right as the foreground

object (upper two panels); the difference image (lower-left) shows the “hole” (where the hand used to be)

toward the left and its leading edge ...