Non-Parametric Outlier Synthesis
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Abstract (arXiv)
Out-of-distribution (OOD) detection is indispensable for safely deploying machine learning models in the wild. One of the key challenges is that models lack supervision signals from unknown data, and as a result, can produce overconfident predictions on OOD data. Recent work on outlier synthesis modeled the feature space as parametric Gaussian distribution, a strong and restrictive assumption that might not hold in reality. In this paper, we propose a novel framework, Non-Parametric Outlier Synthesis (NPOS), which generates artificial OOD training data and facilitates learning a reliable decision boundary between ID and OOD data. Importantly, our proposed synthesis approach does not make any distributional assumption on the ID embeddings, thereby offering strong flexibility and generality. We show that our synthesis approach can be mathematically interpreted as a rejection sampling framework. Extensive experiments show that NPOS can achieve superior OOD detection performance, outperforming the competitive rivals by a significant margin. Code is publicly available at https://github.com/deeplearning-wisc/npos.
Key facts. Cited by 129 papers in the map (data through 7 Oct 2026). Builds on 48 of its 62 references that are in the map. First posted on arXiv 6 Mar 2023.
Builds on
48 of 62 references.
References · 48
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36 more
- 2018Deep Anomaly Detection with Outlier Exposurecited by 939
- 2014Deep Neural Networks are Easily Fooled: High Confidence Predictions for Unrecognizable Imagescited by 774
- 2022Out-of-Distribution Detection with Deep Nearest Neighborscited by 596
- 2018Predictive Uncertainty Estimation via Prior Networkscited by 555
- 2019A Simple Baseline for Bayesian Uncertainty in Deep Learningcited by 555
- 2015Towards Open Set Deep Networkscited by 533
- 2020CSI: Novelty Detection via Contrastive Learning on Distributionally Shifted Instancescited by 441
- 2020Generalized ODIN: Detecting Out-of-distribution Image without Learning from Out-of-distribution Datacited by 408
- 2022ViM: Out-Of-Distribution with Virtual-logit Matchingcited by 404
- 2017Training Confidence-calibrated Classifiers for Detecting Out-of-Distribution Samplescited by 389
- 2020Simple and Principled Uncertainty Estimation with Deterministic Deep Learning via Distance Awarenesscited by 389
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- 2018Why ReLU networks yield high-confidence predictions far away from the training data and how to mitigate the problemcited by 323
- 2022VOS: Learning What You Don't Know by Virtual Outlier Synthesiscited by 300
- 2021Exploring the Limits of Out-of-Distribution Detectioncited by 283
- 2021SSD: A Unified Framework for Self-Supervised Outlier Detectioncited by 264
- 2022Mitigating Neural Network Overconfidence with Logit Normalizationcited by 251
- 2021MOS: Towards Scaling Out-of-distribution Detection for Large Semantic Spacecited by 233
- 2020Being Bayesian, Even Just a Bit, Fixes Overconfidence in ReLU Networkscited by 227
- 2014Towards Open World Recognitioncited by 226
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- 2015TurkerGaze: Crowdsourcing Saliency with Webcam based Eye Trackingcited by 165
- 2022How to Exploit Hyperspherical Embeddings for Out-of-Distribution Detection?cited by 128
- 2022POEM: Out-of-Distribution Detection with Posterior Samplingcited by 108
- 2021Semantically Coherent Out-of-Distribution Detectioncited by 107
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- 2021Can multi-label classification networks know what they don't know?cited by 100
- 2022Training OOD Detectors in their Natural Habitatscited by 86
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Citing papers per year: 2023: 28; 2024: 44; 2025: 40; 2026: 17.
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- 2023OpenOOD v1.5: Enhanced Benchmark for Out-of-Distribution Detectioncited by 178
- 2023LoCoOp: Few-Shot Out-of-Distribution Detection via Prompt Learningcited by 107
- 2024ARGS: Alignment as Reward-Guided Searchcited by 99
- 2024Process Reward Model with Q-Value Rankingscited by 78
- 2023Dream the Impossible: Outlier Imagination with Diffusion Modelscited by 77
- 2024Negative Label Guided OOD Detection with Pretrained Vision-Language Modelscited by 66
- 2025Can We Detect Failures Without Failure Data? Uncertainty-Aware Runtime Failure Detection for Imitation Learning Policiescited by 49
- 2023Fast Decision Boundary based Out-of-Distribution Detectorcited by 48
- 2024Learning with Mixture of Prototypes for Out-of-Distribution Detectioncited by 43
- 2023ID-like Prompt Learning for Few-Shot Out-of-Distribution Detectioncited by 42
- 2023Diversified Outlier Exposure for Out-of-Distribution Detection via Informative Extrapolationcited by 38
- 2023Learning to Augment Distributions for Out-of-Distribution Detectioncited by 38
38 more
- 2023GL-MCM: Global and Local Maximum Concept Matching for Zero-Shot Out-of-Distribution Detectioncited by 36
- 2024How Does Unlabeled Data Provably Help Out-of-Distribution Detection?cited by 36
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- 2023A Survey on Out-of-Distribution Detection in NLPcited by 31
- 2023Out-of-distribution Detection Learning with Unreliable Out-of-distribution Sourcescited by 31
- 2024MultiOOD: Scaling Out-of-Distribution Detection for Multiple Modalitiescited by 28
- 2023DIVERSIFY: A General Framework for Time Series Out-of-distribution Detection and Generalizationcited by 24
- 2024Out-of-Distribution Detection: A Task-Oriented Survey of Recent Advancescited by 24
- 2023A Graph-Theoretic Framework for Understanding Open-World Semi-Supervised Learningcited by 22
- 2024LAPT: Label-driven Automated Prompt Tuning for OOD Detection with Vision-Language Modelscited by 21
- 2024OVOR: OnePrompt with Virtual Outlier Regularization for Rehearsal-Free Class-Incremental Learningcited by 20
- 2024Overcoming the Pitfalls of Vision-Language Model Finetuning for OOD Generalizationcited by 17
- 2024AdaNeg: Adaptive Negative Proxy Guided OOD Detection with Vision-Language Modelscited by 16
- 2025Reliable Few-shot Learning under Dual Noisescited by 16
- 2024Self-Calibrated Tuning of Vision-Language Models for Out-of-Distribution Detectioncited by 15
- 2025GOLD: Graph Out-of-Distribution Detection via Implicit Adversarial Latent Generationcited by 15
- 2023NNG-Mix: Improving Semi-supervised Anomaly Detection with Pseudo-anomaly Generationcited by 14
- 2024Local-Prompt: Extensible Local Prompts for Few-Shot Out-of-Distribution Detectioncited by 14
- 2024CLIPScope: Enhancing Zero-Shot OOD Detection with Bayesian Scoringcited by 13
- 2024Conjugated Semantic Pool Improves OOD Detection with Pre-trained Vision-Language Modelscited by 13
- 2023AUTO: Adaptive Outlier Optimization for Test-Time OOD Detectioncited by 12
- 2023On the Powerfulness of Textual Outlier Exposure for Visual OoD Detectioncited by 12
- 2023Mixture of Gaussian-distributed Prototypes with Generative Modelling for Interpretable and Trustworthy Image Recognitioncited by 11
- 2024Can OOD Object Detectors Learn from Foundation Models?cited by 10
- 2025Compositional Generalization from Learned Skills via CoT Training: A Theoretical and Structural Analysis for Reasoningcited by 10
- 2023Activate and Reject: Towards Safe Domain Generalization under Category Shiftcited by 9
- 2023Model-free Test Time Adaptation for Out-Of-Distribution Detectioncited by 9
- 2024Energy-based Hopfield Boosting for Out-of-Distribution Detectioncited by 9
- 2024SeTAR: Out-of-Distribution Detection with Selective Low-Rank Approximationcited by 9
- 2023Conservative Prediction via Data-Driven Confidence Minimizationcited by 8
- 2024On the Learnability of Out-of-distribution Detectioncited by 8
- 2025Extremely Simple Multimodal Outlier Synthesis for Out-of-Distribution Detection and Segmentationcited by 8
- 2025Adaptive Multi-prompt Contrastive Network for Few-shot Out-of-distribution Detectioncited by 8
- 2024OpenCIL: Benchmarking Out-of-Distribution Detection in Class-Incremental Learningcited by 7
- 2025RODEO: Robust Outlier Detection via Exposing Adaptive Out-of-Distribution Samplescited by 7
- 2025AdaSCALE: Adaptive Scaling for OOD Detectioncited by 7
- 2024CLIP-driven Outliers Synthesis for few-shot OOD detectioncited by 6
- 2024When and How Does In-Distribution Label Help Out-of-Distribution Detection?cited by 6
50 most cited of 129 All 129 (JSON)
- 2026Beyond Empirical Support: Structured Outlier Generation via Sinkhorn Optimal Transport25 Sep 2026
- 2026Score-based Outlier Generation via Controlling the Radon-Nikodym Derivative10 Sep 2026
- 2026MARVEL: Margin-Aware Robust von Mises-Fischer Expert Learning for Long-Tailed Out-of-Distribution Detection2 Jul 2026
- 2026Exploiting Local Flatness for Efficient Out-of-Distribution Detection29 Jun 2026
- 2026MM++: Post-Hoc Scale-Invariant Multilayer OOD Detection via Top-K Gated Feature Fusion15 Jun 2026
- 2026GP-Adapter: Gaussian Process CLIP-Adapter for Few-Shot Out-of-Distribution Detection5 Jun 2026
- 2026Respecting Modality Gap in Post-hoc Out-of-distribution Detection with Pre-trained Vision-Language Models26 May 2026
- 2026Debiased Negative Mining Improves Out-of-distribution Detection with Pre-trained Vision-Language Models22 May 2026
- 2026Early High-Frequency Injection for Geometry-Sensitive OOD Detection20 May 2026
- 2026Mitigating Simplicity Bias in OOD Detection through Object Co-occurrence Analysis8 May 2026
- 2026GEODE: Angle-Adaptive OOD Detection with Universal Scorer Compatibility1 May 2026
- 2026Activation Matters: Test-time Activated Negative Labels for OOD Detection with Vision-Language Models26 Mar 2026
38 more
- 2026Out-of-Distribution Object Detection in Street Scenes via Synthetic Outlier Exposure and Transfer Learning17 Mar 2026
- 2026How to Achieve Prototypical Birth and Death for OOD Detection?6 Mar 2026
- 2026AP-OOD: Attention Pooling for Out-of-Distribution Detection5 Feb 2026
- 2026VMF-GOS: Geometry-guided virtual Outlier Synthesis for Long-Tailed OOD Detection5 Feb 2026
- 2026Learning with Adaptive Prototype Manifolds for Out-of-Distribution Detection5 Feb 2026
- 2025Predictive Sample Assignment for Semantically Coherent Out-of-Distribution Detection15 Dec 2025
- 2025TSRE: Channel-Aware Typical Set Refinement for Out-of-Distribution Detection19 Nov 2025
- 2025BootOOD: Self-Supervised Out-of-Distribution Detection via Synthetic Sample Exposure under Neural Collapse17 Nov 2025
- 2025ClusterMine: Robust Label-Free Visual Out-Of-Distribution Detection via Concept Mining from Text Corpora10 Nov 2025
- 2025GOOD: Training-Free Guided Diffusion Sampling for Out-of-Distribution Detection20 Oct 2025
- 2025Local Background Features Matter in Out-of-Distribution Detection14 Oct 2025
- 2025Equipping Vision Foundation Model with Mixture of Experts for Out-of-Distribution Detection12 Oct 2025
- 2025Hi-OSCAR: Hierarchical Open-set Classifier for Human Activity Recognition8 Oct 2025
- 2025Medix: Out-of-Distribution Detection from Unlabeled Wild Data via Robust Gradient Statistics7 Oct 2025
- 2025Limited Preference Data? Learning Better Reward Model with Latent Space Synthesis30 Sep 2025
- 2025Long-Tailed Out-of-Distribution Detection with Refined Separate Class Learning21 Sep 2025
- 2025Segmentation Assisted Incremental Test Time Adaptation in an Open World27 Aug 2025
- 2025Hierarchical Vision-Language Learning for Medical Out-of-Distribution Detection25 Aug 2025
- 2025Retrieval-Augmented Prompt for OOD Detection14 Aug 2025
- 2025Generalized Few-Shot Out-of-Distribution Detection7 Aug 2025
- 2025BOOD: Boundary-based Out-Of-Distribution Data Generation1 Aug 2025
- 2025Synthesizing Near-Boundary OOD Samples for Out-of-Distribution Detection14 Jul 2025
- 2025NegRefine: Refining Negative Label-Based Zero-Shot OOD Detection13 Jul 2025
- 2025FA: Forced Prompt Learning of Vision-Language Models for Out-of-Distribution Detection6 Jul 2025
- 2025Out-of-Distribution Detection with Adaptive Top-K Logits Integration1 Jul 2025
- 2025Adaptive Multi-prompt Contrastive Network for Few-shot Out-of-distribution Detection21 Jun 2025
- 2025Reliable Few-shot Learning under Dual Noises19 Jun 2025
- 2025Balanced Hyperbolic Embeddings Are Natural Out-of-Distribution Detectors11 Jun 2025
- 2025Open-Set Domain Generalization through Spectral-Spatial Uncertainty Disentanglement for Hyperspectral Image Classification11 Jun 2025
- 2025Proxy-FDA: Proxy-based Feature Distribution Alignment for Fine-tuning Vision Foundation Models without Forgetting30 May 2025
- 2025Extremely Simple Multimodal Outlier Synthesis for Out-of-Distribution Detection and Segmentation22 May 2025
- 2025Graph Synthetic Out-of-Distribution Exposure with Large Language Models29 Apr 2025
- 2025Dream-Box: Object-wise Outlier Generation for Out-of-Distribution Detection25 Apr 2025
- 2025Enhancing Out-of-Distribution Detection with Extended Logit Normalization15 Apr 2025
- 2025EOOD: Entropy-based Out-of-distribution Detection4 Apr 2025
- 2025Can We Detect Failures Without Failure Data? Uncertainty-Aware Runtime Failure Detection for Imitation Learning Policies11 Mar 2025
- 2025AdaSCALE: Adaptive Scaling for OOD Detection11 Mar 2025
- 2025OpenEarthSensing: Large-Scale Fine-Grained Benchmark for Open-World Remote Sensing28 Feb 2025
50 newest of 129 All 129 (JSON)
- 2024Negative Label Guided OOD Detection with Pretrained Vision-Language Modelscited by 66
- 2024LAPT: Label-driven Automated Prompt Tuning for OOD Detection with Vision-Language Modelscited by 21
- 2024Overcoming the Pitfalls of Vision-Language Model Finetuning for OOD Generalizationcited by 17
- 2024AdaNeg: Adaptive Negative Proxy Guided OOD Detection with Vision-Language Modelscited by 16
- 2024Self-Calibrated Tuning of Vision-Language Models for Out-of-Distribution Detectioncited by 15
- 2024Conjugated Semantic Pool Improves OOD Detection with Pre-trained Vision-Language Modelscited by 13
- 2024Category-Extensible Out-of-Distribution Detection via Hierarchical Context Descriptionscited by 6
- 2025Mitigating the Modality Gap: Few-Shot Out-of-Distribution Detection with Multi-modal Prototypes and Image Bias Estimationcited by 3
- 2025FA: Forced Prompt Learning of Vision-Language Models for Out-of-Distribution Detectioncited by 3
- 2025Synthesizing Near-Boundary OOD Samples for Out-of-Distribution Detectioncited by 3
- 2024Reflexive Guidance: Improving OoDD in Vision-Language Models via Self-Guided Image-Adaptive Concept Generationcited by 2
- 2025NegRefine: Refining Negative Label-Based Zero-Shot OOD Detectioncited by 2
12 most cited of 16 All 16 (JSON)
- 2026Respecting Modality Gap in Post-hoc Out-of-distribution Detection with Pre-trained Vision-Language Models26 May 2026
- 2026Debiased Negative Mining Improves Out-of-distribution Detection with Pre-trained Vision-Language Models22 May 2026
- 2026Activation Matters: Test-time Activated Negative Labels for OOD Detection with Vision-Language Models26 Mar 2026
- 2025ClusterMine: Robust Label-Free Visual Out-Of-Distribution Detection via Concept Mining from Text Corpora10 Nov 2025
- 2025Synthesizing Near-Boundary OOD Samples for Out-of-Distribution Detection14 Jul 2025
- 2025NegRefine: Refining Negative Label-Based Zero-Shot OOD Detection13 Jul 2025
- 2025FA: Forced Prompt Learning of Vision-Language Models for Out-of-Distribution Detection6 Jul 2025
- 2025Mitigating the Modality Gap: Few-Shot Out-of-Distribution Detection with Multi-modal Prototypes and Image Bias Estimation2 Feb 2025
- 2024Self-Calibrated Tuning of Vision-Language Models for Out-of-Distribution Detection5 Nov 2024
- 2024AdaNeg: Adaptive Negative Proxy Guided OOD Detection with Vision-Language Models26 Oct 2024
- 2024Reflexive Guidance: Improving OoDD in Vision-Language Models via Self-Guided Image-Adaptive Concept Generation19 Oct 2024
- 2024Conjugated Semantic Pool Improves OOD Detection with Pre-trained Vision-Language Models11 Oct 2024
12 newest of 16 All 16 (JSON)
- 2023Dream the Impossible: Outlier Imagination with Diffusion Modelscited by 77
- 2025GOOD: Training-Free Guided Diffusion Sampling for Out-of-Distribution Detectioncited by 5
- 2025BOOD: Boundary-based Out-Of-Distribution Data Generationcited by 4
- 2024Enhancing OOD Detection Using Latent Diffusioncited by 1
- 2025Dream-Box: Object-wise Outlier Generation for Out-of-Distribution Detectioncited by 1
- 2026Score-based Outlier Generation via Controlling the Radon-Nikodym Derivativecited by 0
- 2026Score-based Outlier Generation via Controlling the Radon-Nikodym Derivative10 Sep 2026
- 2025GOOD: Training-Free Guided Diffusion Sampling for Out-of-Distribution Detection20 Oct 2025
- 2025BOOD: Boundary-based Out-Of-Distribution Data Generation1 Aug 2025
- 2025Dream-Box: Object-wise Outlier Generation for Out-of-Distribution Detection25 Apr 2025
- 2024Enhancing OOD Detection Using Latent Diffusion24 Jun 2024
- 2023Dream the Impossible: Outlier Imagination with Diffusion Models23 Sep 2023
- 2024ARGS: Alignment as Reward-Guided Searchcited by 99
- 2024Out-of-Distribution Learning with Human Feedbackcited by 6
- 2025Limited Preference Data? Learning Better Reward Model with Latent Space Synthesiscited by 2
- 2025Limited Preference Data? Learning Better Reward Model with Latent Space Synthesis30 Sep 2025
- 2024Out-of-Distribution Learning with Human Feedback14 Aug 2024
- 2024ARGS: Alignment as Reward-Guided Search23 Jan 2024
- 2025Retrieval-Augmented Prompt for OOD Detectioncited by 0
- 2025Retrieval-Augmented Prompt for OOD Detection14 Aug 2025
- 2023OpenOOD v1.5: Enhanced Benchmark for Out-of-Distribution Detectioncited by 178
- 2023LoCoOp: Few-Shot Out-of-Distribution Detection via Prompt Learningcited by 107
- 2023Fast Decision Boundary based Out-of-Distribution Detectorcited by 48
- 2024Learning with Mixture of Prototypes for Out-of-Distribution Detectioncited by 43
- 2023ID-like Prompt Learning for Few-Shot Out-of-Distribution Detectioncited by 42
- 2023Diversified Outlier Exposure for Out-of-Distribution Detection via Informative Extrapolationcited by 38
- 2023Learning to Augment Distributions for Out-of-Distribution Detectioncited by 38
- 2023GL-MCM: Global and Local Maximum Concept Matching for Zero-Shot Out-of-Distribution Detectioncited by 36
- 2024How Does Unlabeled Data Provably Help Out-of-Distribution Detection?cited by 36
- 2024Outlier detection by ensembling uncertainty with negative objectnesscited by 34
- 2023A Survey on Out-of-Distribution Detection in NLPcited by 31
- 2023Out-of-distribution Detection Learning with Unreliable Out-of-distribution Sourcescited by 31
12 most cited of 99 All 99 (JSON)
- 2026Beyond Empirical Support: Structured Outlier Generation via Sinkhorn Optimal Transport25 Sep 2026
- 2026MARVEL: Margin-Aware Robust von Mises-Fischer Expert Learning for Long-Tailed Out-of-Distribution Detection2 Jul 2026
- 2026Exploiting Local Flatness for Efficient Out-of-Distribution Detection29 Jun 2026
- 2026MM++: Post-Hoc Scale-Invariant Multilayer OOD Detection via Top-K Gated Feature Fusion15 Jun 2026
- 2026GP-Adapter: Gaussian Process CLIP-Adapter for Few-Shot Out-of-Distribution Detection5 Jun 2026
- 2026Early High-Frequency Injection for Geometry-Sensitive OOD Detection20 May 2026
- 2026Mitigating Simplicity Bias in OOD Detection through Object Co-occurrence Analysis8 May 2026
- 2026GEODE: Angle-Adaptive OOD Detection with Universal Scorer Compatibility1 May 2026
- 2026Out-of-Distribution Object Detection in Street Scenes via Synthetic Outlier Exposure and Transfer Learning17 Mar 2026
- 2026How to Achieve Prototypical Birth and Death for OOD Detection?6 Mar 2026
- 2026AP-OOD: Attention Pooling for Out-of-Distribution Detection5 Feb 2026
- 2026VMF-GOS: Geometry-guided virtual Outlier Synthesis for Long-Tailed OOD Detection5 Feb 2026
12 newest of 99 All 99 (JSON)