Deep hashing has attracted broad interest in cross-modal retrieval because of its low cost and efficient retrieval benefits. To capture the semantic information of raw samples and alleviate the semantic gap, supervised cross-modal hashing methods that utilize label information which could map raw samples from different modalities into a unified common space, are proposed. Although making great progress, existing deep cross-modal hashing methods are suffering from some problems, such as: 1) Considering multi-label cross-modal retrieval, proxy-based methods ignore the data-to-data relations and fail to explore the combination of the different categories profoundly, which could lead to some samples without common categories being embedded in the vicinity; 2) For feature representation, image feature extractors containing multiple convolutional layers cannot fully obtain global information of images, which results in the generation of sub-optimal binary hash codes. In this paper, by extending the proxy-based mechanism to multi-label cross-modal retrieval, we propose a novel Deep Semantic-aware Proxy Hashing (DSPH) framework, which could embed multi-modal multi-label data into a uniform discrete space and capture fine-grained semantic relations between raw samples. Specifically, by learning multi-modal multi-label proxy terms and multi-modal irrelevant terms jointly, the semantic-aware proxy loss is designed to capture multi-label correlations and preserve the correct fine-grained similarity ranking among samples, alleviating inter-modal semantic gaps. In addition, for feature representation, two transformer encoders are proposed as backbone networks for images and text, respectively, in which the image transformer encoder is introduced to obtain global information of the input image by modeling long-range visual dependencies. We have conducted extensive experiments on three baseline multi-label datasets, and the experimental results show that our DSPH framework achieves better performance than state-of-the-art cross-modal hashing methods. The code for the implementation of our DSPH framework is available at https://github.com/QinLab-WFU/DSPH.

Driven by the high nonlinearity of deep neural networks, deep hashing has achieved the pictured great potential in cross-modal retrieval applications, significantly bridging the modality gap. Current deep cross-modal hashing usually utilizes affinity matching or local ranking to capture the local semantic relationships in the learned common space, leading to high neighborhood ambiguity. Simultaneously, most of these frameworks utilize additional regularization terms or margin thresholds to enhance the overall performance, in which searching the model's hyper-parameters under mass training data would have a substantial overhead. In this paper, with a novel extension of information-theoretic measures, a novel deep cross-modal hashing method, named Deep Neighborhood-preserving Hashing (DNpH), is designed to learn a highly separable discrete space, effectively mitigating the semantic gap across different modalities. Specifically, to minimize neighborhood ambiguity, the Quadratic Spherical Mutual Information (QSMI) is first introduced into deep cross-modal hashing to separate neighbors and non-neighbors well, while it is free of tuning parameters during model training compared with other similarity measures. To optimize quadratic mutual information loss smoothly, a square clamping method is developed to improve the stability of model optimization, avoiding converging on bad local optimum. Besides, two transformer encoders are exploited as feature extractors for multi-modal samples to learn the informative semantic representations. Finally, we compare our proposed DNpH framework with various state-of-the-art cross-modal hashing on four public datasets, and large amounts of experiment results demonstrate our contributions and show that DNpH outperforms the compared baselines on different evaluation metrics. The corresponding code is available at https://github.com/QinLab-WFU/DNpH.

Due to its low storage cost and high retrieval efficiency, hashing technology is popularly applied in both academia and industry, which provides an interesting solution for cross-modal similarity retrieval. However, most existing supervised cross-modal hashing methods typically view the fixed-level semantic affinity defined by manual labels as supervised signals to guide hash learning, which only represents a small subset of complex semantic relations between multi-modal samples, thus impeding the hash function learning and degrading the obtained hash codes. In the paper, by learning shared hierarchy proxies, a novel deep cross-modal hashing framework, called Deep Hierarchy-aware Proxy Hashing (DHaPH), is proposed to construct the semantic hierarchy in a data-driven manner, thereby capturing the accurate fine-grained semantic relationships and achieving small intra-class scatter and big inter-class scatter. Specifically, by regarding the hierarchical proxies as learnable ancestors, a novel hierarchy-aware proxy loss is designed to model the latent semantic hierarchical structures from different modalities without prior hierarchy knowledge, in which similar samples share the same Lowest Common Ancestor (LCA) and dissimilar points have different LCA. Meanwhile, to adequately capture valuable semantic information from hard pairs, a multi-modal self-paced loss is introduced into cross-modal hashing to reweight multi-modal pairs dynamically, which enables the model to gradually focus on hard pairs while simultaneously learning universal patterns from multi-modal pairs. Extensive experiments on three available benchmark databases demonstrate that our proposed DHaPH framework outperforms the compared baselines with different evaluation metrics.

Cross-modal retrieval methods based on hashing have gained significant attention in both academic and industrial research. Deep learning techniques have played a crucial role in advancing supervised cross-modal hashing methods, leading to significant practical improvements. Despite these achievements, current deep cross-modal hashing still encounters some underexplored limitations. Specifically, most of the available deep hashing usually utilizes pair-wise or triplet-wise strategies to promote the separation of the inter-classes by calculating the relative similarities between samples, weakening the compactness of intra-class data from different modalities, which could generate ambiguous neighborhoods. In this article, the Deep Neighborhood-aware Proxy Hashing (DNPH) framework is proposed to learn a discriminative embedding space with the original neighborhood relation preserved. By introducing learnable shared category proxies, the neighborhood-aware proxy loss is proposed to project the heterogeneous data into a unified common embedding, in which the sample is pulled closer to the corresponding category proxy and is pushed away from other proxies, capturing small within-class scatter and big between-class scatter. To enhance the quality of the obtained binary codes, the uniform distribution constraint is developed to make each hash bit independently obey the discrete uniform distribution. In addition, the discrimination loss is designed to preserve modality-specific semantic information of samples. Extensive experiments are performed on three benchmark datasets to prove that our proposed DNPH framework achieves comparable or even better performance compared with the state-of-the-art cross-modal retrieval applications. The corresponding code implementation of our DNPH framework is as follows: https://github.com/QinLab-WFU/OUR-DNPH .

Deep hashing integrates the advantages of deep learning and hashing technology, and has become the mainstream of the large-scale image retrieval field. However, when training the deep hashing models, most of the existing approaches regard the similarity margin of image pairs as a constant. Once similarity distance exceeds the fixed margin, the network will not learn anything, which easily results in model collapses. In this paper, we address this dilemma with a novel unified deep hashing framework, termed Deep Neighborhood Structure-preserving Hashing (DNSH), to generate the similarity-preserving and discriminative hash codes. Specifically, by extracting the discriminative object characteristics with large variances, we design an adaptive margin quadruplet loss to further explore the underlying similarity relationship between image pairs, reflecting the correct semantic structure among its neighbors. Based on the quadruple form, we develop a quadruple regularization to decrease quantization errors between binary-like embedding and hashing codes. Furthermore, through learning bit balance and bit independent terms jointly, we present the binary code constraint loss to alleviate redundancy in different bits. Extensive evaluations on four popular benchmark datasets demonstrate that our proposed deep hashing framework achieves an excellent performance than the comparison methods.