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A Dataset for Semantic Segmentation in the Presence of Unknowns
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Introduces ISSU, a real-world Indian-road driving segmentation dataset with 19 known classes plus an anomaly label, static and temporal test splits, and benchmarks state-of-the-art anomaly segmentation methods under closed-set and open-set protocols.
Problem
Existing anomaly segmentation datasets for driving evaluate only anomalies (binary known vs. anomaly) and lack in-domain training data and closed-set plus anomaly labels, so models cannot be evaluated for both knowns and unknowns in realistic, cluttered conditions.
Approach
A fully annotated semantic segmentation dataset from cluttered Indian roads that labels both 19 Cityscapes-style known classes and an anomaly class in test sets, with static and temporal (cross-sensor dashcam video) splits and controlled cross-domain, lighting, and anomaly-size evaluations enabling K+1 open-set evaluation.
Key results
- Mask-level methods trained with OOD data (e.g., RbA, EAM, UNO) reach roughly 95% TPR and FPR under 5% on in-domain static road anomaly evaluation, but performance drops sharply in cross-domain and temporal setups.
- Closed-set IoU on ISSU is about 10% lower than on Cityscapes for in-domain static setup and 20-30% lower for in-domain temporal and cross-domain setups.
- In cross-domain static and temporal setups, UNO detects 79% and 70% of anomalies, but reaching 95% TPR results in FPR above 90%.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Train and evaluate in-domain rather than cross-domain | Mask2Former anomaly segmentation methods · ISSU-Test-Static road anomaly | AP: 79.1 vs. 56.4 | Helped |
| Train and evaluate in-domain rather than cross-domain | Mask2Former anomaly segmentation methods · ISSU-Test-Temporal road anomaly | AP: 37.7 vs. 24.6; 30.4 vs. 37.2 | Mixed |
| Use the temporal test data with the different sensor setup instead of static test data | In-domain anomaly segmentation methods · ISSU road anomaly | AP: 79.1 -> 37.7; 76.8 -> 38.7 | Hurt |
| Evaluate under lowlight conditions rather than day conditions (ablation) | EAM · ISSU-Test-Static road anomaly | AP: 77.72 -> 73.92 | Hurt |
| Evaluate under lowlight conditions rather than day conditions (ablation) | EAM · ISSU-Test-Temporal road anomaly | AP: 47.48 -> 37.68 | Hurt |
| Evaluate under lowlight conditions rather than day conditions (ablation) | PixOOD · ISSU-Test-Static road anomaly | AP: 34.24 -> 5.63 | Hurt |
| Evaluate under lowlight conditions rather than day conditions (ablation) | RbA · ISSU-Test-Temporal road anomaly | AP: 39.82 -> 24.16 | Hurt |
| Evaluate on larger rather than small anomalies (ablation) | EAM · ISSU-Test-Static road anomaly | F1: 39.7 -> 73.7 | Helped |
| Evaluate on very large rather than large anomalies (ablation) | EAM · ISSU-Test-Static road anomaly | F1: 73.7 -> 68.2 | Hurt |
| Evaluate on larger rather than small anomalies (ablation) | PixOOD · ISSU-Test-Temporal road anomaly | F1: 17.9 -> 60; 60 -> 47.9 | Mixed |
| Evaluate on larger rather than small anomalies (ablation) | Mask2Former-based methods · ISSU-Test-Temporal road anomaly | F1 | Hurt |
| Evaluate only road regions rather than all image regions (ablation) | Pixel-level anomaly segmentation methods · ISSU road obstacle evaluation | FPRT | Helped |
Surprising findings
- Pixel-level methods generalize better than mask-level methods from Cityscapes to ISSU in road obstacle evaluation, yielding lower FPR.
- Mask2Former-based methods that perform well in-domain struggle with the temporal sensor shift, showing high FPR.
Limitations
- Anomaly labels are limited to objects on or within 2 m of the road, so unknowns outside the region of interest are not annotated.
- Temporal test set is collected with a consumer dashcam of lower quality, confounding sensor and domain shift.
- Dataset is collected only on Indian roads, limiting geographic diversity.
Experimental setup
Datasets: ISSU-Train Cityscapes
Benchmarks: ISSU-Test-Static ISSU-Test-Temporal
Metrics: AP FPR at 95% TPR TPR at 5% FPR IoU oIoU F1
Baselines: JSR-Net DaCUP PixOOD RbA EAM Pebal UNO Mask2Anomaly
Builds on: Mask2Former Cityscapes SMIYC benchmark
Closest papers by meaning
- MetaUAS: Universal Anomaly Segmentation with One-Prompt Meta-Learning (NeurIPS 2024 · similarity 0.88)
- Spotting the Unexpected (STU): A 3D LiDAR Dataset for Anomaly Segmentation in Autonomous Driving (CVPR 2025 · similarity 0.88)
- Generalize or Detect? Towards Robust Semantic Segmentation Under Multiple Distribution Shifts (NeurIPS 2024 · similarity 0.86)
- Open-World Semantic Segmentation Including Class Similarity (CVPR 2024 · similarity 0.86)
- AnomalyGPT: Detecting Industrial Anomalies Using Large Vision-Language Models (AAAI 2024 · similarity 0.86)
- Self-Supervised Likelihood Estimation with Energy Guidance for Anomaly Segmentation in Urban Scenes (AAAI 2024 · similarity 0.85)
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