In some event detection applications, events of interest occur over a relatively small proportion of the total time: . alarm generation in surveillance systems, and extrac- tive summarization of raw video events. The automatic de- tection of temporal events that are relevant, but whose oc- currence rate is either expected to be very low or cannot be anticipated at all, constitutes a problem which has recently attracted attention in computer vision and multimodal pro- cessing under an umbrella of names (abnormal, unusual, or rare events) [17, 19, 6]. In this paper we employ the term unusual event, which we define as events with the following properties: (1) they seldom occur (rarity);.
