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Unsupervised anomaly detection (UAD) aims to detect anomalies without labeled data, a necessity in many machine learning applications where anomalous samples are rare or not available. Most state-of-the-art methods fall into two categories:…

Machine Learning · Computer Science 2025-07-30 Nicolas Pinon , Carole Lartizien

Dynamic graph anomaly detection (DGAD) is critical for many real-world applications but remains challenging due to the scarcity of labeled anomalies. Existing methods are either unsupervised or semi-supervised: unsupervised methods avoid…

Machine Learning · Computer Science 2026-02-24 Yuxing Tian , Yiyan Qi , Fengran Mo , Weixu Zhang , Jian Guo , Jian-Yun Nie

Unsupervised out-of-distribution (U-OOD) detection has recently attracted much attention due its importance in mission-critical systems and broader applicability over its supervised counterpart. Despite this increase in attention, U-OOD…

Computer Vision and Pattern Recognition · Computer Science 2022-07-22 Lars Doorenbos , Raphael Sznitman , Pablo Márquez-Neila

We consider the problem of anomaly detection with a small set of partially labeled anomaly examples and a large-scale unlabeled dataset. This is a common scenario in many important applications. Existing related methods either exclusively…

Machine Learning · Computer Science 2021-06-11 Guansong Pang , Anton van den Hengel , Chunhua Shen , Longbing Cao

Anomalies are samples that significantly deviate from the rest of the data and their detection plays a major role in building machine learning models that can be reliably used in applications such as data-driven design and novelty…

Machine Learning · Statistics 2023-06-19 Amin Yousefpour , Mehdi Shishehbor , Zahra Zanjani Foumani , Ramin Bostanabad

Deep unsupervised approaches are gathering increased attention for applications such as pathology detection and segmentation in medical images since they promise to alleviate the need for large labeled datasets and are more generalizable…

Computer Vision and Pattern Recognition · Computer Science 2023-08-01 Ioannis Lagogiannis , Felix Meissen , Georgios Kaissis , Daniel Rueckert

Existing approaches towards anomaly detection~(AD) often rely on a substantial amount of anomaly-free data to train representation and density models. However, large anomaly-free datasets may not always be available before the inference…

Computer Vision and Pattern Recognition · Computer Science 2024-03-01 Jingyi Liao , Xun Xu , Manh Cuong Nguyen , Adam Goodge , Chuan Sheng Foo

Medical anomaly detection is a crucial yet challenging task aimed at recognizing abnormal images to assist in diagnosis. Due to the high-cost annotations of abnormal images, most methods utilize only known normal images during training and…

Computer Vision and Pattern Recognition · Computer Science 2023-03-21 Yu Cai , Hao Chen , Xin Yang , Yu Zhou , Kwang-Ting Cheng

Anomaly detection is being regarded as an unsupervised learning task as anomalies stem from adversarial or unlikely events with unknown distributions. However, the predictive performance of purely unsupervised anomaly detection often fails…

Machine Learning · Computer Science 2014-01-27 Nico Goernitz , Marius Micha Kloft , Konrad Rieck , Ulf Brefeld

Fully Unsupervised Anomaly Detection (FUAD) is a practical extension of Unsupervised Anomaly Detection (UAD), aiming to detect anomalies without any labels even when the training set may contain anomalous samples. To achieve FUAD, we…

Computer Vision and Pattern Recognition · Computer Science 2025-08-26 Xinyue Liu , Jianyuan Wang , Biao Leng , Shuo Zhang

Background: With the ever-increasing amount of medical imaging data, the demand for algorithms to assist clinicians has amplified. Unsupervised anomaly detection (UAD) models promise to aid in the crucial first step of disease detection.…

Anomaly detection (AD) is the identification of data samples that do not fit a learned data distribution. As such, AD systems can help physicians to determine the presence, severity, and extension of a pathology. Deep generative models,…

Image and Video Processing · Electrical Eng. & Systems 2021-04-12 Jaime Simarro , Ezequiel de la Rosa , Thijs Vande Vyvere , David Robben , Diana M. Sima

Mainstream unsupervised anomaly detection algorithms often excel in academic datasets, yet their real-world performance is restricted due to the controlled experimental conditions involving clean training data. Addressing the challenge of…

Machine Learning · Computer Science 2025-05-13 Thi Kieu Khanh Ho , Narges Armanfard

Deep neural networks are known to be vulnerable to unseen data: they may wrongly assign high confidence stcores to out-distribuion samples. Recent works try to solve the problem using representation learning methods and specific metrics. In…

Computer Vision and Pattern Recognition · Computer Science 2022-06-07 Haowei He , Jiaye Teng , Yang Yuan

Anomaly detection or more generally outliers detection is one of the most popular and challenging subject in theoretical and applied machine learning. The main challenge is that in general we have access to very few labeled data or no…

Machine Learning · Computer Science 2023-05-31 Mansour Zoubeirou A Mayaki , Michel Riveill

Anomaly detection is a challenging task that frequently arises in practically all areas of industry and science, from fraud detection and data quality monitoring to finding rare cases of diseases and searching for new physics. Most of the…

Machine Learning · Computer Science 2021-11-22 Artem Ryzhikov , Maxim Borisyak , Andrey Ustyuzhanin , Denis Derkach

Unsupervised anomaly detection (UAD) has evolved from building specialized single-class models to unified multi-class models, yet existing multi-class models significantly underperform the most advanced one-for-one counterparts. Moreover,…

Computer Vision and Pattern Recognition · Computer Science 2025-10-27 Jia Guo , Shuai Lu , Lei Fan , Zelin Li , Donglin Di , Yang Song , Weihang Zhang , Wenbing Zhu , Hong Yan , Fang Chen , Huiqi Li , Hongen Liao

Unsupervised Anomaly detection (AD) requires building a notion of normalcy, distinguishing in-distribution (ID) and out-of-distribution (OOD) data, using only available ID samples. Recently, large gains were made on this task for the domain…

Computer Vision and Pattern Recognition · Computer Science 2022-03-22 Mohamed Yousef , Marcel Ackermann , Unmesh Kurup , Tom Bishop

Semi-supervised anomaly detection (SSAD) methods have demonstrated their effectiveness in enhancing unsupervised anomaly detection (UAD) by leveraging few-shot but instructive abnormal instances. However, the dominance of homogeneous normal…

Machine Learning · Computer Science 2023-09-07 Yixuan Zhou , Peiyu Yang , Yi Qu , Xing Xu , Zhe Sun , Andrzej Cichocki

Conventional unsupervised anomaly detection (UAD) methods build separate models for each object category. Recent studies have proposed to train a unified model for multiple classes, namely model-unified UAD. However, such methods still…

Computer Vision and Pattern Recognition · Computer Science 2024-04-17 Jia Guo , Haonan Han , Shuai Lu , Weihang Zhang , Huiqi Li