SAM2-UNet

SAM2-UNet: Segment Anything 2 Makes Strong Encoder for Natural and Medical Image Segmentation

Xinyu Xiong, Zihuang Wu, Shuangyi Tan, Wenxue Li, Feilong Tang, Ying Chen, Siying Li, Jie Ma, Guanbin Li

Introduction

Image segmentation plays an important role in vision understanding. Recently, the emerging vision foundation models continuously achieved superior performance on various tasks. Following such success, in this paper, we prove that the Segment Anything Model 2 (SAM2) can be a strong encoder for U-shaped segmentation models. We propose a simple but effective framework, termed SAM2-UNet, for versatile image segmentation. Specifically, SAM2-UNet adopts the Hiera backbone of SAM2 as the encoder, while the decoder uses the classic U-shaped design. Additionally, adapters are inserted into the encoder to allow parameter-efficient fine-tuning. Preliminary experiments on various downstream tasks, such as camouflaged object detection, salient object detection, marine animal segmentation, mirror detection, and polyp segmentation, demonstrate that our SAM2-UNet can simply beat existing specialized state-of-the-art methods without bells and whistles.

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Clone Repository

git clone https://github.com/WZH0120/SAM2-UNet.git
cd SAM2-UNet/

Prepare Datasets

You can refer to the following repositories and their papers for the detailed configurations of the corresponding datasets.

• Camouflaged Object Detection. Please refer to FEDER. [#issue #13, #44]
• Salient Object Detection. Please refer to SALOD.
• Marine Animal Segmentation. Please refer to MASNet.
• Mirror Detection. Please refer to HetNet.
• Polyp Segmentation. Please refer to PraNet.

Requirements

Our project does not depend on installing SAM2. If you have already configured an environment for SAM2, then directly using this environment should also be fine. You may also create a new conda environment:

conda create -n sam2-unet python=3.10
conda activate sam2-unet
pip install -r requirements.txt

Training

If you want to train your own model, please download the pre-trained segment anything 2 (not SAM2.1, [#issue #18, #30]) from the official repository. You can also directly download sam2_hiera_large.pt from here. After the above preparations, you can run train.sh to start your training.

Testing

Our pre-trained models and prediction maps can be found on Google Drive. Also, you can run test.sh to obtain your own predictions.

Evaluation

After obtaining the prediction maps, you can run eval.sh to get most of the quantitative results. For the evaluation of mirror detection, please refer to eval.py in HetNet to obtain the results.

Citation and Star

Please cite the following paper and star this project if you use this repository in your research. Thank you!

@article{xiong2026sam2,
  title={Sam2-unet: Segment anything 2 makes strong encoder for natural and medical image segmentation},
  author={Xiong, Xinyu and Wu, Zihuang and Tan, Shuangyi and Li, Wenxue and Tang, Feilong and Chen, Ying and Li, Siying and Ma, Jie and Li, Guanbin},
  journal={Visual Intelligence},
  volume={4},
  number={1},
  pages={2},
  year={2026},
  publisher={Springer}
}

Acknowledgement

segment anything 2