BRUSH: Label Reconstructing and Similarity Preserving Hashing for Cross-modal Retrieval

Abstract

The hashing technique has recently sparked much attention in information retrieval community due to its high efficiency in terms of storage and query processing. For cross-modal retrieval tasks, existing supervised hashing models either treat the semantic labels as the ground truth and formalize the problem to a classification task, or further add a similarity matrix as supervisory signals to pursue hash codes of high quality to represent coupled data. However, these approaches are incapable of ensuring that the learnt binary codes preserve well the semantics and similarity relationships contained in the supervised information. Moreover, for sophisticated discrete optimization problems, it is always addressed by continuous relaxation or bit-wise solver, which leads to a large quantization error and inefficient computation. To relieve these issues, in this paper, we present a two-step supervised discrete hashing method, i.e., laBel ReconstrUcting and Similarity preserving Hashing (BRUSH). We formulate it as an asymmetric pairwise similarity-preserving problem by using two latent semantic embeddings deducted from decomposing semantics and reconstructing semantics, respectively. Meanwhile, the unified binary codes are jointly generated based on both embeddings with the affinity guarantee, such that the discriminative property of the obtained hash codes can be significantly enhanced alongside preserving semantics well. In addition, by adopting two-step hash learning strategy, our method simplifies the procedure of the hashing function and binary codes learning, thus improving the flexibility and efficiency. The resulting discrete optimization problem is also elegantly solved by the proposed alternating algorithm without any relaxation. Extensive experiments on benchmarks demonstrate that BRUSH outperforms the state-of-the-art methods, in terms of efficiency and effectiveness.