Online hashing has attracted much research attention for large-scale image retrieval in a streaming way. The main challenge lies in keeping balance between high retrieval accuracy and low training time. Existing online hashing methods almost rely on shallow models rather than deep networks due to high training costs, because it is unacceptable to update hash functions on an order of hours. In addition, the multi-label supervision information is not fully utilized to guide the hash learning process and the affinity matrix is always fixed once constructed. In this paper, we propose a novel Deep Graph Online Hashing (DGOH) method, which for the first time introduces inductive graph neural networks (GNNs) to realize deep online hashing with acceptable training costs on an order of seconds. Furthermore, we mine the multi-label information of the images by constructing a label network and learn label-wise weights dynamically to help to update the affinity matrix. In addition, we provide a strategy to obtain examples from the old data to solve the catastrophic forgetting problem. An integrated objective function is designed to train the entire architecture. Extensive experiments on two common benchmarks demonstrate that the proposed method achieves up to 13.3% accuracy gains over state-of-the-art baselines and shows competitive performance on training time.

Trajectory similarity computation is a fundamental problem in various applications (e.g., transportation optimization, behavioral study). Recent researches learn trajectory representations instead of point matching to realize more accurate and efficient trajectory similarity computation. However, these methods can still not be scaled to large datasets due to high computational cost. In this paper, we propose a novel hash learning method to encode the trajectories into binary hash codes and compute trajectory similarities by Hamming distances which is much more efficient. To the best of our knowledge, this is the first work to conduct hash learning for trajectory similarity computation. Furthermore, unlike the Word2Vec model based on random walk strategy, we utilize hypergraph neural networks for the first time to learn the representations for the grids by constructing the hyperedges according to the real-life trajectories, resulting in more representative grid embeddings. In addition, we design a residual network into the multi-layer GRU to learn more discriminative trajectory representations. The proposed Hypergraph Hash Learning for Trajectory similarity commutation is an end-to-end framework and named HHL-Traj. Experimental results on two real-world trajectory datasets (i.e., Porto and Beijing) demonstrate that the proposed framework achieves up to 6.23% and 15.42% accuracy gains compared with state-of-the-art baselines in unhashed and hashed cases, respectively. The efficiency of trajectory similarity computation based on hash codes is also verified. Our code is available at https://github.com/caoyuan57/HHL-Traj.

Hashing has been widely used in large-scale image retrieval due to its high storage and search efficiency. Unsupervised learning saves a significant amount of labor costs compared to supervised learning. Existing unsupervised methods mostly convert unsupervised problems into supervised problems by reconstructing semantic information. In this paper, we propose a novel Self-supervised Adversarial Hashing (SAH) method which utilizes unsupervised semantic reconstruction methods along with self-supervised generative adversarial and contrastive learning methods to improve the model’s accuracy and robustness. In addition, we propose a novel method for semantic relationship reconstruction, taking into account the similarity between different categories. Based on this, we have designed a multi-joint loss to further achieve reasonable intra-class aggregation and inter-class differentiation. The experimental results show that the proposed method outperforms state-of-the-art hashing methods for large-scale image retrieval.

Deep hash networks have garnered significant attention due to their efficiency and ability to learn discriminative embeddings for approximate nearest neighbor search. However, it is observed that deep hash networks are vulnerable to adversarial interference, which is an important security problem. Despite the growing interest in targeted attack on deep hash networks, it suffers from a scarcity of research on generating universal adversarial perturbations which are unrelated to the specific images. In this paper, we introduce a novel Targeted Universal adversarial Attack (TUA) on deep hash networks. Our framework consists of two key components: a ReferenceNet and a universal generative adversarial network. Specifically, ReferenceNet is designed to generate category-level representative reference codes for the target labels by introducing a cosine similarity based reference loss. Additionally, we feed the fixed random noise and target labels into the generator to learn universal adversarial perturbations. Particularly, the reference codes are used to optimize the generator by minimizing the Hamming distances between the hash codes of the adversarial examples and the reference codes. Extensive experiments on three common datasets validate the superior targeted attack performance, transferability, and universality of our method compared with state-of-the-art targeted attack methods on deep hash networks.