In defense of the two-stage framework for open-set domain adaptive semantic segmentation

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Hauptverfasser: Ren, Wenqi, Wang, Weijie, Zheng, Meng, Wu, Ziyan, Tang, Yang, Zhong, Zhun, Sebe, Nicu
Format: Preprint
Veröffentlicht: 2026
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author Ren, Wenqi
Wang, Weijie
Zheng, Meng
Wu, Ziyan
Tang, Yang
Zhong, Zhun
Sebe, Nicu
author_facet Ren, Wenqi
Wang, Weijie
Zheng, Meng
Wu, Ziyan
Tang, Yang
Zhong, Zhun
Sebe, Nicu
contents Open-Set Domain Adaptation for Semantic Segmentation (OSDA-SS) presents a significant challenge, as it requires both domain adaptation for known classes and the distinction of unknowns. Existing methods attempt to address both tasks within a single unified stage. We question this design, as the annotation imbalance between known and unknown classes often leads to negative transfer of known classes and underfitting for unknowns. To overcome these issues, we propose SATS, a Separating-then-Adapting Training Strategy, which addresses OSDA-SS through two sequential steps: known/unknown separation and unknown-aware domain adaptation. By providing the model with more accurate and well-aligned unknown classes, our method ensures a balanced learning of discriminative features for both known and unknown classes, steering the model toward discovering truly unknown objects. Additionally, we present hard unknown exploration, an innovative data augmentation method that exposes the model to more challenging unknowns, strengthening its ability to capture more comprehensive understanding of target unknowns. We evaluate our method on public OSDA-SS benchmarks. Experimental results demonstrate that our method achieves a substantial advancement, with a +3.85% H-Score improvement for GTA5-to-Cityscapes and +18.64% for SYNTHIA-to-Cityscapes, outperforming previous state-of-the-art methods.
format Preprint
id arxiv_https___arxiv_org_abs_2601_01439
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle In defense of the two-stage framework for open-set domain adaptive semantic segmentation
Ren, Wenqi
Wang, Weijie
Zheng, Meng
Wu, Ziyan
Tang, Yang
Zhong, Zhun
Sebe, Nicu
Computer Vision and Pattern Recognition
Open-Set Domain Adaptation for Semantic Segmentation (OSDA-SS) presents a significant challenge, as it requires both domain adaptation for known classes and the distinction of unknowns. Existing methods attempt to address both tasks within a single unified stage. We question this design, as the annotation imbalance between known and unknown classes often leads to negative transfer of known classes and underfitting for unknowns. To overcome these issues, we propose SATS, a Separating-then-Adapting Training Strategy, which addresses OSDA-SS through two sequential steps: known/unknown separation and unknown-aware domain adaptation. By providing the model with more accurate and well-aligned unknown classes, our method ensures a balanced learning of discriminative features for both known and unknown classes, steering the model toward discovering truly unknown objects. Additionally, we present hard unknown exploration, an innovative data augmentation method that exposes the model to more challenging unknowns, strengthening its ability to capture more comprehensive understanding of target unknowns. We evaluate our method on public OSDA-SS benchmarks. Experimental results demonstrate that our method achieves a substantial advancement, with a +3.85% H-Score improvement for GTA5-to-Cityscapes and +18.64% for SYNTHIA-to-Cityscapes, outperforming previous state-of-the-art methods.
title In defense of the two-stage framework for open-set domain adaptive semantic segmentation
topic Computer Vision and Pattern Recognition
url https://arxiv.org/abs/2601.01439