Ranking large scale image and video collections usually expects higher accuracy on top ranked data, while tolerates lower accuracy on bottom ranked ones. In view of this, we propose a rank learning algorithm, called Imbalanced RankBoost, which merges RankBoost and iterative thresholding into a unified loss optimization framework. The proposed approach provides a more efficient ranking process by iteratively identifying a cutoff threshold in each boosting iteration, and automatically truncating ranking feature computation for the data ranked below. Experiments on the TRECVID 2007 high-level feature benchmark show that the proposed approach outperforms RankBoost in terms of both ranking effectiveness and efficiency. It achieves an up to 21% improvement in terms of mean average precision, or equivalently, a 6-fold speedup in the ranking process.
Michele Merler, Rong Yan, John R. Smith