Efficient subtree pruning scheme in tree-structured hierarchy

For efficient image retrieval, most existing methods that adopt a tree-structured hierarchy exploit a subtree pruning scheme, based on the triangle inequality of a distance metric, during the tree traversal. In this paper, we propose a refined pruning scheme for the tree-structured hierarchy by introducing a novel notion of the node distance to subcluster (NDS) and validate it in both theoretical and experimental aspects. Experimental results demonstrate that the proposed method outperforms the existing ones by 10%-25% in terms of retrieval efficiency at the negligible increase of storage for a retrieval system.