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Unsupervised outlier detection is attractive because it eliminates the need for labeled data. Moreover, forming multi-model ensembles can improve detection robustness. However, composing an ensemble without labeled data is challenging.…

Machine Learning · Computer Science 2026-05-19 Hong-Phuc Phan , Tuan-Anh Vu , Tung Kieu , Son Ha Xuan , Bin Yang , Christian S. Jensen

The reliability of artificial intelligence (AI) systems in open-world settings depends heavily on their ability to flag out-of-distribution (OOD) inputs unseen during training. Recent advances in large-scale vision-language models (VLMs)…

Machine Learning · Computer Science 2025-10-14 Faizul Rakib Sayem , Shahana Ibrahim

In this work, we present ODHD, an algorithm for outlier detection based on hyperdimensional computing (HDC), a non-classical learning paradigm. Along with the HDC-based algorithm, we propose IM-ODHD, a computing-in-memory (CiM)…

Hardware Architecture · Computer Science 2024-02-26 Ruixuan Wang , Sabrina Hassan Moon , Xiaobo Sharon Hu , Xun Jiao , Dayane Reis

Outlier detection (OD) has a vast literature as it finds numerous real-world applications. Being an unsupervised task, model selection is a key bottleneck for OD without label supervision. Despite a long list of available OD algorithms with…

Machine Learning · Computer Science 2025-09-26 Yuchen Shen , Haomin Wen , Leman Akoglu

Unsupervised embedding learning aims to extract good representation from data without the need for any manual labels, which has been a critical challenge in many supervised learning tasks. This paper proposes a new unsupervised embedding…

Machine Learning · Computer Science 2020-02-28 Sungwon Han , Yizhan Xu , Sungwon Park , Meeyoung Cha , Cheng-Te Li

Most machine learning algorithms are configured by one or several hyperparameters that must be carefully chosen and often considerably impact performance. To avoid a time consuming and unreproducible manual trial-and-error process to find…

We ask the following question: what training information is required to design an effective outlier/out-of-distribution (OOD) detector, i.e., detecting samples that lie far away from the training distribution? Since unlabeled data is easily…

Computer Vision and Pattern Recognition · Computer Science 2021-03-23 Vikash Sehwag , Mung Chiang , Prateek Mittal

High-dimensional data poses unique challenges in outlier detection process. Most of the existing algorithms fail to properly address the issues stemming from a large number of features. In particular, outlier detection algorithms perform…

Machine Learning · Computer Science 2020-09-22 Firuz Kamalov , Ho Hon Leung

Addressing the Out-of-Distribution (OoD) segmentation task is a prerequisite for perception systems operating in an open-world environment. Large foundational models are frequently used in downstream tasks, however, their potential for OoD…

Computer Vision and Pattern Recognition · Computer Science 2024-09-11 Nazir Nayal , Youssef Shoeb , Fatma Güney

Outlier detection (OD) is a key learning task for finding rare and deviant data samples, with many time-critical applications such as fraud detection and intrusion detection. In this work, we propose TOD, the first tensor-based system for…

Machine Learning · Computer Science 2022-09-20 Yue Zhao , George H. Chen , Zhihao Jia

Out-of-distribution (OOD) detection plays a crucial role in ensuring the robustness and reliability of machine learning systems deployed in real-world applications. Recent approaches have explored the use of unlabeled data, showing…

Machine Learning · Computer Science 2025-10-09 Momin Abbas , Ali Falahati , Hossein Goli , Mohammad Mohammadi Amiri

Most existing deep learning models are trained based on the closed-world assumption, where the test data is assumed to be drawn i.i.d. from the same distribution as the training data, known as in-distribution (ID). However, when models are…

Machine Learning · Computer Science 2022-11-09 Yixin Liu , Kaize Ding , Huan Liu , Shirui Pan

Detecting data points deviating from the training distribution is pivotal for ensuring reliable machine learning. Extensive research has been dedicated to the challenge, spanning classical anomaly detection techniques to contemporary…

Machine Learning · Computer Science 2024-05-30 Xuefeng Du , Yiyou Sun , Yixuan Li

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

Out-of-distribution (OOD) detection is a rapidly growing field due to new robustness and security requirements driven by an increased number of AI-based systems. Existing OOD textual detectors often rely on an anomaly score (e.g.,…

Computation and Language · Computer Science 2024-02-22 Maxime Darrin , Guillaume Staerman , Eduardo Dadalto Câmara Gomes , Jackie CK Cheung , Pablo Piantanida , Pierre Colombo

Existing approaches to unsupervised object discovery (UOD) do not scale up to large datasets without approximations that compromise their performance. We propose a novel formulation of UOD as a ranking problem, amenable to the arsenal of…

Computer Vision and Pattern Recognition · Computer Science 2021-11-18 Huy V. Vo , Elena Sizikova , Cordelia Schmid , Patrick Pérez , Jean Ponce

As deep learning methods form a critical part in commercially important applications such as autonomous driving and medical diagnostics, it is important to reliably detect out-of-distribution (OOD) inputs while employing these algorithms.…

Machine Learning · Computer Science 2018-09-12 Apoorv Vyas , Nataraj Jammalamadaka , Xia Zhu , Dipankar Das , Bharat Kaul , Theodore L. Willke

In this paper, we present a new algorithm for semi-supervised representation learning. In this algorithm, we first find a vector representation for the labels of the data points based on their local positions in the space. Then, we map the…

Machine Learning · Computer Science 2020-08-05 Ershad Banijamali , Ali Ghodsi

In open-set semi-supervised learning (OSSL), we consider unlabeled datasets that may contain unknown classes. Existing OSSL methods often use the softmax confidence for classifying data as in-distribution (ID) or out-of-distribution (OOD).…

Machine Learning · Computer Science 2026-01-26 Erik Wallin , Lennart Svensson , Fredrik Kahl , Lars Hammarstrand

The problem of detecting a small number of outliers in a large dataset is an important task in many fields from fraud detection to high-energy physics. Two approaches have emerged to tackle this problem: unsupervised and supervised.…

Machine Learning · Computer Science 2015-07-30 Barbora Micenková , Brian McWilliams , Ira Assent