Unsupervised Deep Hashing with Structured Similarity Learning.

Hashing technology, one of the most efficient approximate nearest neighbor searching methods due to its fast query speed and low storage cost, has been widely used in image retrieval. Recently, unsupervised deep hashing methods have attracted more and more attention due to the lack of labels in real applications. Most unsupervised hashing methods usually construct a similarity matrix with the features extracted from the images, and then guide the hash code learning with this similarity matrix. However, in unsupervised scenario, such similarity matrix may be unreliable due to the affect of noise and irrelevant objects in images. In this paper, we propose a novel unsupervised deep hashing method called Deep Structured Hashing (DSH). In the new method, we first learn both continuous and binary structured similarity matrices with explicit cluster structure to better preserve the semantic structure, where the binary one preserves the coarse-grained semantic structure while the continuous one preserves the fine-grained semantic structure. And then jointly optimize three kinds of losses to learn high quality hash codes. Extensive experiments on three benchmark datasets show the superior retrieval performance of our proposed method.