Abstract

In this paper we describe our TRECVID 2007 experiments. The MediaMill team participated in two tasks: concept detection and search. For concept detection we extract regionbased image features, on grid, keypoint, and segmentation level, which we combine with various supervised learners. In addition, we explore the utility of temporal image features. A late fusion approach of all region-based analysis methods using geometric mean was our most successful run. What is more, using MediaMill Challenge and LSCOM annotations, our visual-only approach generalizes to a set of 572 concept detectors. To handle such a large thesaurus in retrieval, an engine is developed which automatically selects a set of relevant concept detectors based on text matching, ontology querying, and visual concept likelihood. The suggestion engine is evaluated as part of the automatic search task and forms the entry point for our interactive search experiments. For this task we experiment with two browsers for interactive exploration: the well-known CrossBrowser and the novel ForkBrowser. It was found that, while retrieval performance varies substantially per topic, the ForkBrowser is able to produce the same overall results as the CrossBrowser. However, the ForkBrowser obtains top-performance for most topics with less user interaction. Indicating the potential of this browser for interactive search. Similar to previous years our best interactive search runs yield high overall performance, ranking 3rd and 4th. 1

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