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This paper discusses the effects of the duration of templates in similar play retrieval using
correlation and absolute difference in similar play retrieval on only motions. First, we show
the over-all structure of the proposed method. Then, space-time image is discussed. Next, we
discuss the similarity measures based on correlation and absolute difference. Then, we shows
the experiments on a video of a real baseball game on a Japanese TV broad cast. And last, we
conclude this work.
2 Structure of the proposed method
The proposed play retrieving method is the composition of a correlation and an absolute dif-
ference of motion space-time images [ 1 - 6 ] . We describe the space-time image as ST (space-
time) image in the followings. In MPEG video, each 16 × 16 pixels' block has the motion com-
pensation vector. Using the MPEG motion compensation vector as the motion description, the
size of the description is 1/64 of the original frames. In other word, the static texture descrip-
tion is 64 times larger than the motion descriptions in size. The static texture description is 96
times larger than the motion description in total amount with the consideration of the vector
The color description fits for describing the static scenes. The motion description does for
describing the dynamic scenes. A play in a sport is a composition of motions. Therefore, the
motion description fits for describing plays in a sport. For retrieving the same play in a video,
we can use any similarity measures. However, our goal is the retrieval of similar plays from
videos. The speed of a play may change. In this case, the similarity measure must be robust
about the absolute amount of motions. Our motion retrieval method uses the simple correla-
tion as the similarity measure. The simple correlation works well in the similar play retrieval
in sport videos. Using correlation as the similarity measure, there is no hint for the absolute
amount of motions. As a result, there are some error retrievals. In the relative motion space,
there is no difference between large motions and small motions.
The absolute difference is a major difference feature. In similar play retrieval, the absolute
difference shows poor performance in our preparation experiments [ 10 ] . However, with other
similarity measures the absolute difference can work some role for distinguishing the similar-
ity measured with the correlations.
The proposed similar play retrieving method uses both of the correlation and the absolute
difference between a template ST image and the ST image from videos. We can easily difer-
entiate the large motion difference with the absolute difference. In sport videos, the absolute
difference can find the camera motions. Composing the correlation based measure and the ab-
solute difference based measure, we construct the composite similar play retrieval method.
Figure 1 shows the structure of the proposed method. We use absolute difference and cor-
relation separately. Therefore, there is no need to use same length of templates.
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