Inverse square rank fusion for multimodal search

Rank fusion is the task of combining multiple ranked document lists (ranks) into a single ranked list. It is a late fusion approach designed to improve the rankings produced by individual systems. Rank fusion techniques have been applied throughout multiple domains: e.g. combining results from multiple retrieval functions, or multimodal search where several feature spaces are common. In this paper, we present the Inverse Square Rank fusion method family, a set of novel fully unsupervised rank fusion methods based on quadratic decay and on logarithmic document frequency normalization. Our experiments created with standard Information Retrieval datasets (image and text fusion) and image datasets (image features fusion), show that ISR outperforms existing rank fusion algorithms. Thus, the proposed technique has comparable or better performance than existing state-of-the-art approaches, while maintaining a low computational complexity and avoiding the need for document scores or training data.