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Hierarchical classification is a crucial task in many applications, where objects are organized into multiple levels of categories. However, conventional classification approaches often neglect inherent inter-class relationships at…

Computer Vision and Pattern Recognition · Computer Science 2025-10-02 Julius Ott , Nastassia Vysotskaya , Huawei Sun , Lorenzo Servadei , Robert Wille

Representation learning has significantly been developed with the advance of contrastive learning methods. Most of those methods have benefited from various data augmentations that are carefully designated to maintain their identities so…

Computer Vision and Pattern Recognition · Computer Science 2022-01-24 Xiao Wang , Guo-Jun Qi

Recently, contrastive learning has risen to be a promising approach for large-scale self-supervised learning. However, theoretical understanding of how it works is still unclear. In this paper, we propose a new guarantee on the downstream…

Machine Learning · Computer Science 2022-05-30 Yifei Wang , Qi Zhang , Yisen Wang , Jiansheng Yang , Zhouchen Lin

Unified anomaly detection (AD) is one of the most challenges for anomaly detection, where one unified model is trained with normal samples from multiple classes with the objective to detect anomalies in these classes. For such a challenging…

Machine Learning · Computer Science 2024-07-08 Xincheng Yao , Ruoqi Li , Zefeng Qian , Lu Wang , Chongyang Zhang

Contrastive representation learning has emerged as an outstanding approach for anomaly detection. In this work, we explore the $\ell_2$-norm of contrastive features and its applications in out-of-distribution detection. We propose a simple…

Computer Vision and Pattern Recognition · Computer Science 2024-04-09 Tai Le-Gia , Jaehyun Ahn

What matters for contrastive learning? We argue that contrastive learning heavily relies on informative features, or "hard" (positive or negative) features. Early works include more informative features by applying complex data…

Computer Vision and Pattern Recognition · Computer Science 2023-08-10 Jiangmeng Li , Wenwen Qiang , Changwen Zheng , Bing Su , Hui Xiong

Unsupervised Anomaly Detection (UAD) plays a crucial role in identifying abnormal patterns within data without labeled examples, holding significant practical implications across various domains. Although the individual contributions of…

Machine Learning · Computer Science 2024-06-04 Zeyu Fang , Ming Gu , Sheng Zhou , Jiawei Chen , Qiaoyu Tan , Haishuai Wang , Jiajun Bu

Graph anomaly detection aims to identify abnormal patterns in networks, but faces significant challenges from label scarcity and extreme class imbalance. While graph contrastive learning offers a promising unsupervised solution, existing…

Machine Learning · Computer Science 2026-01-30 Kamal Berahmand , Saman Forouzandeh , Mehrnoush Mohammadi , Parham Moradi , Mahdi Jalili

Label distribution learning (LDL) is a new machine learning paradigm for solving label ambiguity. Since it is difficult to directly obtain label distributions, many studies are focusing on how to recover label distributions from logical…

Machine Learning · Computer Science 2023-05-17 Yifei Wang , Yiyang Zhou , Jihua Zhu , Xinyuan Liu , Wenbiao Yan , Zhiqiang Tian

Graph anomaly detection (GAD) is a vital task in graph-based machine learning and has been widely applied in many real-world applications. The primary goal of GAD is to capture anomalous nodes from graph datasets, which evidently deviate…

Machine Learning · Computer Science 2022-12-05 Jingcan Duan , Siwei Wang , Pei Zhang , En Zhu , Jingtao Hu , Hu Jin , Yue Liu , Zhibin Dong

Anomaly detection is to identify samples that do not conform to the distribution of the normal data. Due to the unavailability of anomalous data, training a supervised deep neural network is a cumbersome task. As such, unsupervised methods…

Computer Vision and Pattern Recognition · Computer Science 2022-07-05 Vahid Reza Khazaie , Anthony Wong , John Taylor Jewell , Yalda Mohsenzadeh

The memory dictionary-based contrastive learning method has achieved remarkable results in the field of unsupervised person Re-ID. However, The method of updating memory based on all samples does not fully utilize the hardest sample to…

Computer Vision and Pattern Recognition · Computer Science 2024-04-09 Lingzhi Liu , Haiyang Zhang , Chengwei Tang , Tiantian Zhang

One main challenge in time series anomaly detection (TSAD) is the lack of labelled data in many real-life scenarios. Most of the existing anomaly detection methods focus on learning the normal behaviour of unlabelled time series in an…

Machine Learning · Computer Science 2024-09-04 Zahra Zamanzadeh Darban , Geoffrey I. Webb , Shirui Pan , Charu C. Aggarwal , Mahsa Salehi

The core challenge in unsupervised anomaly detection is identifying abnormal patterns without prior knowledge of their characteristics. While existing methods have addressed aspects of this problem, they often struggle to learn a robust…

Machine Learning · Computer Science 2026-05-12 Prithul Sarker , Sushmita Sarker , Nicholas G. Murray , Alireza Tavakkoli

Semi-supervised Anomaly Detection (AD) is a kind of data mining task which aims at learning features from partially-labeled datasets to help detect outliers. In this paper, we classify existing semi-supervised AD methods into two…

Machine Learning · Computer Science 2022-10-27 Chao Chen , Dawei Wang , Feng Mao , Zongzhang Zhang , Yang Yu

Anomaly detection is a significant and hence well-studied problem. However, developing effective anomaly detection methods for complex and high-dimensional data remains a challenge. As Generative Adversarial Networks (GANs) are able to…

Machine Learning · Computer Science 2018-12-07 Houssam Zenati , Manon Romain , Chuan Sheng Foo , Bruno Lecouat , Vijay Ramaseshan Chandrasekhar

Anomaly detection is a well-known task that involves the identification of abnormal events that occur relatively infrequently. Methods for improving anomaly detection performance have been widely studied. However, no studies utilizing…

Machine Learning · Computer Science 2025-02-10 Seffi Cohen , Niv Goldshlager , Lior Rokach , Bracha Shapira

Detecting test data deviating from training data is a central problem for safe and robust machine learning. Likelihoods learned by a generative model, e.g., a normalizing flow via standard log-likelihood training, perform poorly as an…

Machine Learning · Computer Science 2023-04-28 Robert Schmier , Ullrich Köthe , Christoph-Nikolas Straehle

Contrastive learning has led to substantial improvements in the quality of learned embedding representations for tasks such as image classification. However, a key drawback of existing contrastive augmentation methods is that they may lead…

Computer Vision and Pattern Recognition · Computer Science 2022-04-19 Zhibo Zhang , Jongseong Jang , Chiheb Trabelsi , Ruiwen Li , Scott Sanner , Yeonjeong Jeong , Dongsub Shim

Outlier detection is an important topic in machine learning and has been used in a wide range of applications. In this paper, we approach outlier detection as a binary-classification issue by sampling potential outliers from a uniform…

Machine Learning · Computer Science 2019-03-19 Yezheng Liu , Zhe Li , Chong Zhou , Yuanchun Jiang , Jianshan Sun , Meng Wang , Xiangnan He