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Improving the Generalization of Segmentation Foundation Model under Distribution Shift via Weakly Supervised Adaptation
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Adapts SAM (ViT-B) to shifted downstream segmentation tasks via source-free weakly supervised self-training with an anchor network, contrastive regularization, and LoRA on the encoder, using box/point/polygon prompts as weak supervision.
Problem
SAM generalizes poorly under strong distribution shift (corrupted, camouflaged, medical, robotic images), and adapting a large foundation model is costly and often infeasible without source data or target labels.
Approach
Source-free self-training of SAM's image encoder where a frozen source anchor network regularizes teacher/student predictions, a feature-level contrastive loss regularizes encoder outputs, weak prompts (box, points, coarse polygon) produce cleaner pseudo labels, and only low-rank LoRA weights are updated.
Key results
- On COCO with box prompts, the method reaches 80.12 mIoU vs 74.29 for direct SAM and 77.29 for WDASS, approaching the supervised upper bound of 81.50.
- On camouflaged CHAMELEON with point prompts, the method improves over direct SAM by roughly 35 mIoU points (39.37 to 74.00).
- On COCO-C corruptions with box prompts, average mIoU rises from 66.73 (direct) to 71.05, outperforming all competing adaptation methods on average.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| adapt SAM with weakly supervised self-training, anchor regularization, and low-rank finetuning | SAM ViT-B · COCO-C, box prompt (average) | mIoU: 66.73 -> 71.05 | Helped |
| adapt SAM with weakly supervised self-training, anchor regularization, and low-rank finetuning | SAM ViT-B · COCO 2017, box prompt | mIoU: 74.29 -> 80.12 | Helped |
| adapt SAM with weakly supervised self-training, anchor regularization, and low-rank finetuning | SAM ViT-B · kvasir-SEG, box prompt | mIoU: 81.59 -> 85.47 | Helped |
| adapt SAM with weakly supervised self-training, anchor regularization, and low-rank finetuning | SAM ViT-B · ISIC, box prompt | mIoU: 66.74 -> 80.01 | Helped |
| adapt SAM with weakly supervised self-training, anchor regularization, and low-rank finetuning | SAM ViT-B · CHAMELEON, box prompt | mIoU: 51.32 -> 75.94 | Helped |
| adapt SAM with weakly supervised self-training, anchor regularization, and low-rank finetuning | SAM ViT-B · OSD, box prompt | mIoU: 87.62 -> 92.11 | No clear effect |
| add anchor-loss regularization to self-training (ablation) | weakly supervised SAM adaptation · COCO, box prompt | mIoU: 58.88 -> 79.65 | Helped |
| add contrastive loss to the adaptation objective (ablation) | weakly supervised SAM adaptation · COCO, box prompt | mIoU: 79.65 -> 80.12 | Helped |
| use low-rank encoder adaptation instead of full encoder finetuning (ablation) | SAM ViT-B · COCO, box prompt | mIoU: 78.54 -> 80.12 | Helped |
| finetune MaskDecoder instead of using LoRA (ablation) | SAM ViT-B · COCO, box prompt | mIoU: 80.12 -> 76.81 | Hurt |
| tune explicit visual prompts instead of using LoRA (ablation) | SAM ViT-B · COCO, box prompt | mIoU: 80.12 -> 77.38 | Hurt |
Surprising findings
- Self-training alone causes a large performance drop (COCO box: 74.29 to 58.88) due to confirmation bias, which the anchor loss largely remedies.
- Updating only LoRA in the image encoder outperforms full encoder finetuning (80.12 vs 78.54 IoU) in the ablation.
Limitations
- Relies on ground-truth-derived simulated weak prompts (boxes, 5+5 points, polygons) for training and testing, not real human annotations.
- Uses ViT-B encoder only due to memory constraints; larger SAM variants not evaluated.
- Point-prompt results on some datasets (e.g., COCO without weak supervision) are worse than direct SAM, and the method is not uniformly best (e.g., CAMO poly, OSD point).
Experimental setup
Datasets: COCO Pascal VOC COCO-C Kvasir-SEG ISIC COD10K CHAMELEON CAMO OCID OSD SA-1B
Benchmarks: COCO COCO-C Pascal VOC Kvasir-SEG ISIC CHAMELEON CAMO COD10K OCID OSD
Metrics: mIoU
Baselines: Direct (pre-trained SAM) TENT SHOT Soft Teacher TRIBE DePT WDASS Supervised upper bound
Builds on: Segment Anything (SAM) SHOT LoRA WDASS Soft Teacher
Closest papers by meaning
- TinySAM: Pushing the Envelope for Efficient Segment Anything Model (AAAI 2025 · similarity 0.88)
- Enhancing SAM with Efficient Prompting and Preference Optimization for Semi-supervised Medical Image Segmentation (CVPR 2025 · similarity 0.87)
- From SAM to CAMs: Exploring Segment Anything Model for Weakly Supervised Semantic Segmentation (CVPR 2024 · similarity 0.87)
- Uncertainty-aware Fine-tuning of Segmentation Foundation Models (NeurIPS 2024 · similarity 0.87)
- RobustSAM: Segment Anything Robustly on Degraded Images (CVPR 2024 · similarity 0.87)
- BLO-SAM: Bi-level Optimization Based Finetuning of the Segment Anything Model for Overfitting-Preventing Semantic Segmentation (ICML 2024 · similarity 0.87)
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