Learning reconfigurable hashing for diverse semantics

In recent years, locality-sensitive hashing (LSH) has gained plenty of attention from both the multimedia and computer vision communities due to its empirical success and theoretic guarantee in large-scale visual indexing and retrieval. Conventional LSH algorithms are designated either for generic metrics such as Cosine similarity, ℓ2-norm and Jaccard index, or for the metrics learned from user-supplied supervision information. The common drawbacks of existing algorithms are their incapability to be adapted to metric changes, along with the inefficacy when handling diverse semantics (e. g., more than 1K different categories in the well-known ImageNet database). For the metrics underlying the hashing structure, even tiny changes tend to nullify previous indexing efforts, which motivates our proposed framework towards "reconfigurable hashing". The basic idea is to maintain a large pool of over-complete hashing functions embedded in the ambient feature space, which serves as the common infrastructure of high-level diverse semantics. At the runtime, the algorithm dynamically selects relevant hashing bits by maximizing the consistency to specific semantics-induced metric, thereby achieving reusability of the pre-computed hashing bits. Such a reusable scheme especially benefits the indexing and retrieval of large-scale dataset, since it facilitates one-off indexing rather than continuous computation-intensive maintenance towards metric adaptation. We propose a sequential bit-selection algorithm based on local consistency and global regularization. Extensive studies are conducted on large-scale image benchmarks to comparatively investigate the performance of different strategies on reconfigurable hashing. Despite the vast literature on hashing, to our best knowledge rare endeavors have been spent toward the reusability of hashing structures in large-scale datasets.