The widespread adoption of graph neural networks (GNNs) has brought increased attention to fairness issues related to sensitive attributes, such as gender and race, in practical scenarios. However, this concern remains largely unexplored in the context of graph clustering. Conventional fair graph clustering methods primarily depend on spectral clustering approaches. Meanwhile, we argue that existing graph learning works mainly focus on a single type of fairness, whereas graph clustering should achieve group equality-informed individual fairness. In this paper, we introduce for the first time a fairness-aware framework termed FairGC for deep graph clustering, which integrates the dual objectives of individual and group fairness while maintaining accurate clustering results. Specifically, we construct two views with distinct semantics using Siamese encoders. Then, we apply multi-step random walks on view-specific affinity graphs to capture high-order affinities of node pairs, thereby reformulating the contrastive learning with a focus on individual similarity. Besides, we utilize adversarial learning by making node representations independent of the estimated sensitive attributes to further eliminate group biases of clustering results. Extensive experiments on four benchmarks demonstrate the effectiveness and superiority of our proposed framework FairGC.

Domain adaptive hashing has received increasing attention since it is capable of enhancing the performance of retrieval if the target domain for testing meets domain shift. However, owing to data security and transmission constraints nowadays, abundant source data is often not available. Towards this end, this paper investigates a novel yet practical problem named test-time adaptive hashing, which aims to enhance the performance of hashing models without access to the source domain data when tested on the target domain with domain shift. This problem is challenging due to both fugacious domain shift and label scarcity on the target domain. In this paper, we propose a novel hashing approach namedDiscrepancy andStructure-basedContrast (DISC) for effective test-time adaptive retrieval. In particular, DISC first trains the hashing model using the source domain data and stores the distribution of each class in the hidden space. During test-time adaptation, we generate simulated source features based on stored distributions and compare class-specific distributions across domains using maximum mean discrepancy (MMD) to overcome potential domain shift. Furthermore, to tackle the label scarcity, we estimate the graph structure using deep features on the target domain, which guides effective hashing contrastive learning for generating discriminative and domain-invariant hash codes. Extensive experiments on various benchmark datasets validate the superiority of our proposed DISC compared with a range of competing baselines.

This article studies deep unsupervised hashing, which has attracted increasing attention in large-scale image retrieval. The majority of recent approaches usually reconstruct semantic similarity information, which then guides the hash code learning. However, they still fail to achieve satisfactory performance in reality for two reasons. On the one hand, without accurate supervised information, these methods usually fail to produce independent and robust hash codes with semantics information well preserved, which may hinder effective image retrieval. On the other hand, due to discrete constraints, how to effectively optimize the hashing network in an end-to-end manner with small quantization errors remains a problem. To address these difficulties, we propose a novel unsupervised hashing method called HARR to learn discriminative and high-quality hash codes. To comprehensively explore semantic similarity structure, HARR adopts the Winner-Take-All hash to model the similarity structure. Then similarity-preserving hash codes are learned under the reliable guidance of the reconstructed similarity structure. Additionally, we improve the quality of hash codes by a bit correlation reduction module, which forces the cross-correlation matrix between a batch of hash codes under different augmentations to approach the identity matrix. In this way, the generated hash bits are expected to be invariant to disturbances with minimal redundancy, which can be further interpreted as an instantiation of the information bottleneck principle. Finally, for effective hashing network training, we minimize the cosine distances between real-value network outputs and their binary codes for small quantization errors. Extensive experiments demonstrate the effectiveness of our proposed HARR.

Although graph neural networks (GNNs) have achieved impressive achievements in graph classification, they often need abundant task-specific labels, which could be extensively costly to acquire. A credible solution is to explore additional labeled graphs to enhance unsupervised learning on the target domain. However, how to apply GNNs to domain adaptation remains unsolved owing to the insufficient exploration of graph topology and the significant domain discrepancy. In this paper, we propose Coupled Contrastive Graph Representation Learning (CoCo), which extracts the topological information from coupled learning branches and reduces the domain discrepancy with coupled contrastive learning. CoCo contains a graph convolutional network branch and a hierarchical graph kernel network branch, which explore graph topology in implicit and explicit manners. Besides, we incorporate coupled branches into a holistic multi-view contrastive learning framework, which not only incorporates graph representations learned from complementary views for enhanced understanding, but also encourages the similarity between cross-domain example pairs with the same semantics for domain alignment. Extensive experiments on popular datasets show that our CoCo outperforms these competing baselines in different settings generally.

Thanks for the cross-modal retrieval techniques, visible-infrared (RGB-IR) person re-identification (Re-ID) is achieved by projecting them into a common space, allowing person Re-ID in 24-hour surveillance systems. However, with respect to the probe-to- gallery, almost all existing RGB-IR based cross-modal person Re-ID methods focus on image-to-image matching, while the video-to-video matching which contains much richer spatial- and temporal-information remains under-explored. In this paper, we primarily study the video-based cross-modal per-son Re-ID method. To achieve this task, a video-based RGB-IR dataset is constructed, in which 927 valid identities with 463,259 frames and 21,863 tracklets captured by 12 RGB/IR cameras are collected. Based on our constructed dataset, we prove that with the increase of frames in a tracklet, the performance does meet more enhancement, demonstrating the significance of video-to-video matching in RGB-IR person Re-ID. Additionally, a novel method is further proposed, which not only projects two modalities to a modal-invariant subspace, but also extracts the temporal-memory for motion-invariant. Thanks to these two strategies, much better results are achieved on our video-based cross-modal person Re-ID. The code and dataset are released at: https://github.com/VCM-project233/MITML.

Hashing is widely used in large-scale image retrieval because of its efficiency in storage and computation. Although longer hash codes can lead to higher search accuracy, the retrieval cost increases linearly with the increase of the number of hash bits. Most deep hashing methods suffer from the problem of trivial solutions and usually result in highly correlated redundant hash bits in practice, which limits the performance. To obtain short hash codes with high quality for fast and accurate image retrieval, we propose a novel framework named Deep Hashing via Weight Pruning (DHWP). DHWP first trains the model with relatively long hash codes. Then it obtains shorter codes gradually by weight pruning based on four different criteria. The framework of DHWP can be applied to most deep supervised hashing models, which helps remove those redundant hash bits while retaining the representation ability of long hash codes. Extensive experimental results on two widely used benchmark datasets show that DHWP outperforms the existing state-of-the-art methods, especially for short hash codes.

In this paper, we study deep unsupervised hashing, a critical problem for approximate nearest neighbor research. Most recent methods solve this problem by semantic similarity reconstruction for guiding hashing network learning or contrastive learning of hash codes. However, in multi-label scenarios, these methods usually either generate an inaccurate similarity matrix without reflection of similarity ranking or suffer from the violation of the underlying assumption in contrastive learning, resulting in limited retrieval performance. To tackle this issue, we propose a novel method termed HAMAN, which explores semantics from a fine-grained view to enhance the ability of multi-label image retrieval. In particular, we reconstruct the pairwise similarity structure by matching fine-grained patch features generated by the pre-trained neural network, serving as reliable guidance for similarity preserving of hash codes. Moreover, a novel conditional contrastive learning on hash codes is proposed to adopt self-supervised learning in multi-label scenarios. According to extensive experiments on three multi-label datasets, the proposed method outperforms a broad range of state-of-the-art methods.

Hashing has become increasingly popular in approximate nearest neighbor search in recent years due to its storage and computational efficiency. While deep unsupervised hashing has shown encouraging performance recently, its efficacy in the more realistic unsupervised situation is far from satisfactory due to two limitations. On one hand, they usually neglect the underlying global semantic structure in the deep feature space. On the other hand, they also ignore reconstructing the global structure in the hash code space. In this research, we develop a simple yet effective approach named deeP U nsupeR vised hashing via P rototypical LEarning.. Specifically, introduces both feature prototypes and hashing prototypes to model the underlying semantic structures of the images in both deep feature space and hash code space. Then we impose a smoothness constraint to regularize the consistency of the global structures in two spaces through our semantic prototypical consistency learning. Moreover, our method encourages the prototypical consistency for different augmentations of each image via contrastive prototypical consistency learning. Comprehensive experiments on three benchmark datasets demonstrate that our proposed performs better than a variety of state-of-the-art retrieval methods.

Hashing has attracted increasing attention in image retrieval recently due to its storage and computational efficiency. Although several deep unsupervised hashing methods have been proposed lately, their effectiveness is far from satisfactory in practice owing to two drawbacks. On the one hand, they mostly construct binary similarity matrices which could neglect the confidence differences among multiple similarity signals. On the other hand, they ignore the desired properties of hash codes (i.e., independence and robustness). In this paper, we propose an effective unsupervised hashing method calledHashing viaStructural andIntrinsic siMilarity learning (HashSIM) to tackle these issues in an end-to-end manner. Specifically, HashSIM utilizes both highly and normally confident image pairs to jointly build a continuous similarity matrix, which guides hash code learning via structural similarity learning. Moreover, inspired by contrastive learning, we impose an intrinsic similarity learning objective, which can maximally satisfy the independence and robustness properties of hash bits. Extensive experiments on three popular benchmark datasets demonstrate that our HashSIM outperforms a broad range of state-of-the-art baselines.

Rapid and accurate prediction of user preferences is the ultimate goal of today’s recommender systems. More and more researchers pay attention to multi-behavior recommender systems which utilize the auxiliary types of user-item interaction data, such as page view and add-to-cart to help estimate user preferences. Recently, graph-based methods were proposed to showcase an advanced capability in representation learning and capturing collaborative signals. However, we argue that these methods ignore the intrinsic difference between the two types of nodes in the bipartite graph and aggregate information from neighboring nodes with the same functions. Besides, these models do not fully explore the collaborative signals implied by the meta-path across different types of behavior, which causes a huge loss of the potential semantic information across behaviors. To address the above limitations, we present a unified graph model named SaGCN (short for Semantic-aware Graph Convolutional Networks). Specifically, we construct separate user-user and item-item graphs by meta-path, and apply separate aggregation and transformation functions to propagate user and item information. To perform better semantic propagation, we design a relation composition function and a semantic propagation architecture for heterogeneous collaborative filtering signals learning. Extensive experiments on two real-world datasets show that SaGCN outperforms a wide range of state-of-the-art methods in multi-behavior scenarios.

Hashing has been widely used in approximate nearest neighbor search recently. Deep supervised hashing methods are not widely-used because of the lack of labeled data, especially when the domain is transferred. Meanwhile, unsupervised deep hashing models can hardly achieve satisfactory performance due to the lack of reliable similarity signals. Here, we propose a novel deep unsupervised hashing method, namely Distilled Smooth Guidance (DSG), which can learn a distilled dataset consisting of similarity signals as well as smooth confidence signals. Specifically, we obtain the similarity confidence weights based on the initial noisy similarity signals learned from local structures and construct a priority loss function for smooth similarity-preserving learning. Besides, global information based on clustering is utilized to distill the image pairs by removing contradictory similarity signals. Extensive experiments on three widely used bench-mark datasets show that the proposed DSG consistently out-performs the state-of-the-art search methods.

Recently, hashing is widely used in approximate nearest neighbor search for its storage and computational efficiency. Most of the unsupervised hashing methods learn to map images into semantic similarity-preserving hash codes by constructing local semantic similarity structure from the pre-trained model as the guiding information, i.e., treating each point pair similar if their distance is small in feature space. However, due to the inefficient representation ability of the pre-trained model, many false positives and negatives in local semantic similarity will be introduced and lead to error propagation during the hash code learning. Moreover, few of the methods consider the robustness of models, which will cause instability of hash codes to disturbance. In this paper, we propose a new method named Comprehensive sImilarity Mining and cOnsistency learNing (CIMON). First, we use global refinement and similarity statistical distribution to obtain reliable and smooth guidance. Second, both semantic and contrastive consistency learning are introduced to derive both disturb-invariant and discriminative hash codes. Extensive experiments on several benchmark datasets show that the proposed method outperforms a wide range of state-of-the-art methods in both retrieval performance and robustness.

With the increasing scale and diversification of interaction behaviors in E-commerce, more and more researchers pay attention to multi-behavior recommender systems which utilize interaction data of other auxiliary behaviors. However, all existing models ignore two kinds of intrinsic heterogeneity which are helpful to capture the difference of user preferences and the difference of item attributes. First (intra-heterogeneity), each user has multiple social identities with otherness, and these different identities can result in quite different interaction preferences. Second (inter-heterogeneity), each item can transfer an item-specific percentage of score from low-level behavior to high-level behavior for the gradual relationship among multiple behaviors. Thus, the lack of consideration of these heterogeneities damages recommendation rank performance. To model the above heterogeneities, we propose a novel method named intrA- and inteR-heteroGeneity recOmmendation model (ARGO). Specifically, we embed each user into multiple vectors representing the user's identities, and the maximum of identity scores indicates the interaction preference. Besides, we regard the item-specific transition percentage as trainable transition probability between different behaviors. Extensive experiments on two real-world datasets show that ARGO performs much better than the state-of-the-art in multi-behavior scenarios.

The majority of deep unsupervised hashing methods usually first construct pairwise semantic similarity information and then learn to map images into compact hash codes while preserving the similarity structure, which implies that the quality of hash codes highly depends on the constructed semantic similarity structure. However, since the features of images for each kind of semantics usually scatter in high-dimensional space with unknown distribution, previous methods could introduce a large number of false positives and negatives for boundary points of distributions in the local semantic structure based on pairwise cosine distances. Towards this limitation, we propose a general distribution-based metric to depict the pairwise distance between images. Specifically, each image is characterized by its random augmentations that can be viewed as samples from the corresponding latent semantic distribution. Then we estimate the distances between images by calculating the sample distribution divergence of their semantics. By applying this new metric to deep unsupervised hashing, we come up with Distribution-based similArity sTructure rEconstruction (DATE). DATE can generate more accurate semantic similarity information by using non-parametric ball divergence. Moreover, DATE explores both semantic-preserving learning and contrastive learning to obtain high-quality hash codes. Extensive experiments on several widely-used datasets validate the superiority of our DATE.