Benefiting from low storage requirements, high search efficiency, and promising performance, online hashing has attracted considerable attention for large-scale streaming data retrieval. However, most existing online hashing methods implicitly assume that the label space is fixed and fail to effectively handle the label incremental problem. With this motivation, in this article, we introduce a novel supervised online hashing framework named Incremental Plug-and-play Online Hashing (IPOH), which endows prevailing methods with the ability to solve the above issues. Specifically, IPOH could extract the patterns of old classes from the learned hash codes at the last round and then generate the class-wise representations for unseen new labels. With these representations, we could learn the hash codes for streaming data with new labels. Experimental results on two widely used datasets demonstrate the effectiveness of our method in handling class incremental data. We hope this article could convince more researchers to look into this interesting problem, and the source code for the implementation of our IPOH framework has been released at https://github.com/ZCyueternal/IPOH.git .

Few-Shot Class-Incremental Learning (FSCIL) aims to continuously learn new classes from limited samples while preventing catastrophic forgetting. With the increasing distribution of learning data across different clients and privacy concerns, FSCIL faces a more realistic scenario where few learning samples are distributed across different clients, thereby necessitating a Federated Few-Shot Class-Incremental Learning (FedFSCIL) scenario. However, this integration faces challenges from non-IID problem, which affects model generalization and training efficiency. The communication overhead in federated settings also presents a significant challenge. To address these issues, we propose Class-Aware Prompting for Federated Few-Shot Class-Incremental Learning (FedCAP). Our framework leverages pre-trained models enhanced by a class-wise prompt pool, where shared class-wise keys enable clients to utilize global class information during training. This unifies the understanding of base class features across clients and enhances model consistency. We further incorporate a class-level information fusion module to improve class representation and model generalization. Our approach requires very few parameter transmission during model aggregation, ensuring communication efficiency. To our knowledge, this is the first study to explore the scenario of FedFSCIL. Consequently, we designed comprehensive experimental setups and made the code publicly available.

Deep Cross-Modal Hashing (CMH) has become one of the most popular solutions for cross-modal retrieval. Existing methods need to first collect data and then be trained with these accumulated data. However, in real world, data may be generated and possessed by different owners. Considering the concerns about privacy, data may not be shared or transmitted, leading to the failure of sufficient training of CMH. To solve the problem, we propose a new framework called Federated Cross-modal Hashing with Adaptive Feature Enhancement (FedCAFE). FedCAFE is a federated method which could use distributed data to train existing CMH methods under the privacy protection. To overcome the data heterogeneity challenge of distributed data and improve the generalization ability of global model, FedCAFE is endowed with a novel adaptive feature enhancement module and a new weighted aggregation strategy. Besides, it could fully utilize the rich global information carried in the global model to constrain the model during the local training process. We have conducted extensive experiments on four widely-used datasets in CMH domain with both IID and non-IID settings. The reported results demonstrate that the proposed FedCAFE achieves better performance than several state-of-the-art baselines.

With the continuous generation of massive amounts of multimedia data nowadays, hashing has demonstrated significant potentials for large-scale search. To handle the emerging needs for streaming data retrieval, online hashing is drawing more and more attention. For online scenario, data distribution may change and concept drifts may occur as new data is continuously added to the database. Inevitably, hashing models may lose or disrupt the previously obtained knowledge when learning from new information, which is called the problem of catastrophic forgetting. In this paper, we propose a new online hashing method called Self-distillation Dual-memory Online Hashing with Hash Centers, which is abbreviated to SDOH-HC, to overcome this challenge. Specifically, SDOH-HC contains replay and distillation modules. For replay, a dual-memory mechanism is proposed which involves hash centers and exemplars. For knowledge distillation, we let hash centers distill information from themselves, i.e., the version of last round. Additionally, a new objective function is further built on above modules and is solved discretely to learn hash codes. Extensive experiments on three benchmark datasets demonstrate the effectiveness of our method.