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Detection of periodic patterns of interest within noisy time series data plays a critical role in various tasks, spanning from health monitoring to behavior analysis. Existing learning techniques often rely on labels or clean versions of…

Machine Learning · Computer Science 2025-06-24 Berken Utku Demirel , Christian Holz

One pivot challenge for image anomaly (AD) detection is to learn discriminative information only from normal class training images. Most image reconstruction based AD methods rely on the discriminative capability of reconstruction error.…

Computer Vision and Pattern Recognition · Computer Science 2020-07-21 Dongyun Lin , Yiqun Li , Shudong Xie , Tin Lay Nwe , Sheng Dong

Subsequence anomaly detection in long sequences is an important problem with applications in a wide range of domains. However, the approaches proposed so far in the literature have severe limitations: they either require prior domain…

Machine Learning · Computer Science 2022-07-26 Paul Boniol , Themis Palpanas

So-called unsupervised anomaly detection is better described as semi-supervised, as it assumes all training data are nominal. This assumption simplifies training but requires manual data curation, introducing bias and limiting adaptability.…

Computer Vision and Pattern Recognition · Computer Science 2025-10-29 Muhammad Aqeel , Shakiba Sharifi , Marco Cristani , Francesco Setti

Numerous methods for time-series anomaly detection (TSAD) have emerged in recent years, most of which are unsupervised and assume that only normal samples are available during the training phase, due to the challenge of obtaining abnormal…

Machine Learning · Computer Science 2024-08-08 Thomas Lai , Thi Kieu Khanh Ho , Narges Armanfard

As large-scale time-series data can easily be found in real-world applications, multivariate time-series anomaly detection has played an essential role in diverse industries. It enables productivity improvement and maintenance cost…

Machine Learning · Computer Science 2022-02-22 Heejeong Choi , Subin Kim , Pilsung Kang

Unsupervised domain adaptation (UDA) aims to transfer and adapt knowledge from a labeled source domain to an unlabeled target domain. Traditionally, subspace-based methods form an important class of solutions to this problem. Despite their…

Machine Learning · Computer Science 2022-01-07 Kowshik Thopalli , Jayaraman J Thiagarajan , Rushil Anirudh , Pavan K Turaga

Unsupervised tabular anomaly detection methods typically learn feature patterns from normal samples during training and subsequently identify samples that deviate from these patterns as anomalies during testing. However, in practical…

Machine Learning · Computer Science 2026-05-12 Wei Huang , Hezhe Qiao , Kailai Zhang , Zaisheng Ye , Yu-Ming Shang , Xiangling Fu

Anomaly detection is widely used in network intrusion detection, autonomous driving, medical diagnosis, credit card frauds, etc. However, several key challenges remain open, such as lack of ground truth labels, presence of complex temporal…

Machine Learning · Computer Science 2023-03-24 Shyam Sundar Saravanan , Tie Luo , Mao Van Ngo

Anomalies are ubiquitous in all scientific fields and can express an unexpected event due to incomplete knowledge about the data distribution or an unknown process that suddenly comes into play and distorts observations. Due to such events'…

Computer Vision and Pattern Recognition · Computer Science 2021-12-14 Fabio Valerio Massoli , Fabrizio Falchi , Alperen Kantarci , Şeymanur Akti , Hazim Kemal Ekenel , Giuseppe Amato

The research in anomaly detection lacks a unified definition of what represents an anomalous instance. Discrepancies in the nature itself of an anomaly lead to multiple paradigms of algorithms design and experimentation. Predictive…

Time series are ubiquitous and occur naturally in a variety of applications -- from data recorded by sensors in manufacturing processes, over financial data streams to climate data. Different tasks arise, such as regression, classification…

Machine Learning · Computer Science 2024-09-17 Sebastian Wette , Florian Heinrichs

Recent efforts towards video anomaly detection (VAD) try to learn a deep autoencoder to describe normal event patterns with small reconstruction errors. The video inputs with large reconstruction errors are regarded as anomalies at the test…

Computer Vision and Pattern Recognition · Computer Science 2021-09-03 Yuandu Lai , Yahong Han , Yaowei Wang

One-class anomaly detection aims to detect objects that do not belong to a predefined normal class. In practice training data lack those anomalous samples; hence state-of-the-art methods are trained to discriminate between normal and…

Computer Vision and Pattern Recognition · Computer Science 2025-03-10 Romain Hermary , Vincent Gaudillière , Abd El Rahman Shabayek , Djamila Aouada

Contrastive Analysis (CA) detects anomalies by contrasting patterns unique to a target group (e.g., unhealthy subjects) from those in a background group (e.g., healthy subjects). In the context of brain MRIs, existing CA approaches rely on…

Computer Vision and Pattern Recognition · Computer Science 2025-07-02 Cristiano Patrício , Carlo Alberto Barbano , Attilio Fiandrotti , Riccardo Renzulli , Marco Grangetto , Luis F. Teixeira , João C. Neves

Anomalies are intuitively easy for human experts to understand, but they are hard to define mathematically. Therefore, in order to have performance guarantees in unsupervised anomaly detection, priors need to be assumed on what the…

Machine Learning · Statistics 2020-04-08 Tiago Pimentel , Marianne Monteiro , Adriano Veloso , Nivio Ziviani

Medical imaging data suffers from the limited availability of annotation because annotating 3D medical data is a time-consuming and expensive task. Moreover, even if the annotation is available, supervised learning-based approaches suffer…

Image and Video Processing · Electrical Eng. & Systems 2020-11-12 Abinav Ravi Venkatakrishnan , Seong Tae Kim , Rami Eisawy , Franz Pfister , Nassir Navab

Recent studies highlighted a practical setting of unsupervised anomaly detection (UAD) that builds a unified model for multi-class images. Despite various advancements addressing this challenging task, the detection performance under the…

Computer Vision and Pattern Recognition · Computer Science 2025-04-03 Jia Guo , Shuai Lu , Weihang Zhang , Fang Chen , Huiqi Li , Hongen Liao

Time-series anomaly detection plays a vital role in monitoring complex operation conditions. However, the detection accuracy of existing approaches is heavily influenced by pattern distribution, existence of multiple normal patterns,…

Machine Learning · Computer Science 2022-02-08 Min Hu , Yi Wang , Xiaowei Feng , Shengchen Zhou , Zhaoyu Wu , Yuan Qin

Despite their irresistible success, deep learning algorithms still heavily rely on annotated data. On the other hand, unsupervised settings pose many challenges, especially about determining the right inductive bias in diverse scenarios.…

Computer Vision and Pattern Recognition · Computer Science 2021-03-11 Beril Besbinar , Pascal Frossard