XRCE’s Participation to ImageCLEF 2008
This year, our participation to ImageCLEF 2008 (Photo Retrieval sub-task) was motivated by trying to address three different problems: visual concept detection and its exploitation in a retrieval context, multimedia fusion methods for improved retrieval performance and diversity-based re-ranking methods. From a purely visual perspective, the representation based on Fisher vectors derived from a generative mixture model appeared to be efficient for both visual concept detection and content-based image retrieval. From a multimedia perspective, we used an intermediate fusion approach, based on cross-media relevance feedback that can be seen as a multigraph-based query regularization method with alternating steps. The combination allowed to improve both mono-media systems by more than 50\% (relative). Finally, as one of main goals of the organizers was to promote both relevance and diversity in the retrieval outputs, we designed and assessed several re-ranking strategies that turned out to preserve standard retrieval performance (such at precision at 20 or mean average precision) while significantly decreasing the redundancy in the top documents.