“…I MAGE retrieval is an important technique for many multimedia applications, such as face retrieval [19], object retrieval [7], and landmark identification [6]. For large-scale image retrieval tasks, one of the key components is an effective indexing method for similarity search [47], [5], particularly on high-dimensional feature space [24], [48], [36], [42]. Similarity search, a.k.a., nearest neighbor (NN) search, is a fundamental problem.…”