Real-time feature extraction from video stream data for stream ...

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Real-time feature extraction from video stream data for stream ...

2.2. Shot Boundary Detection

approaches for the detection of hard cuts will most likely fail on gradual transitions.

Intuitively we would try to lower the threshold, but unfortunately it turns out that in

many cases the difference values resulting from a gradual transitions will be smaller

than the difference values of successive frames resulting from camera movements, zooming

or panning. Because of that we need techniques that enable us to distinguish between

gradual transistions and special camera effects.

Twin comparison

The twin comparison approach has been developed by Zhang, Kankanhalli, and Smoliar

[Zhang et al., 1993]. Instead of using just one threshold, this approach bases on a lower

threshold T l and a higher threshold T h . Whenever the difference of one frame towards

its’ previous frame exceeds the lower threshold T l , the frame gets declared as the potential

start of a gradual transition F s . As long as the difference value of two successive

frames does not drop under the threshold T l , these frames are compared to the potential

starting frame F s , resulting in an accumulated difference value. If this accumulated

difference value exceeds the higher threshold T h , which is by the way also used to detect

hard cuts, the end of a gradual transition F e is detected. If the difference value

between two consecutive frames drops below T l before the accumulated difference value

exceeds T h , the potential start point F s is dropped and no shot boundary is declared.

The approach is illustrated in figure 2.7, taken from the comparison paper of Ahanger

[Ahanger and Little, 1996].

Figure 2.7.: Illustration of the twin comparison approach. Figure taken from

[Ahanger and Little, 1996].

Unfortunately the approach is not robust towards special camera effects. Hence we still

have the problem to distinguish between gradual transitions and special camera effects.

This can be done by using motion vectors.

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