Hierarchical Transformer
for Efficient Image Super-Resolution

Xiang Zhang¹ · Yulun Zhang² · Fisher Yu¹

¹ETH Zürich     ²MoE Key Lab of Artificial Intelligence, Shanghai Jiao Tong University

ECCV 2024 - Oral

[Paper] | [Supp] | [Visual Results] | [Models]

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Abstract: Transformers have exhibited promising performance in computer vision tasks including image super-resolution (SR). However, popular transformer-based SR methods often employ window self-attention with quadratic computational complexity to window sizes, resulting in fixed small windows with limited receptive fields. In this paper, we present a general strategy to convert transformer-based SR networks to hierarchical transformers (HiT-SR), boosting SR performance with multi-scale features while maintaining an efficient design. Specifically, we first replace the commonly used fixed small windows with expanding hierarchical windows to aggregate features at different scales and establish long-range dependencies. Considering the intensive computation required for large windows, we further design a spatial-channel correlation method with linear complexity to window sizes, efficiently gathering spatial and channel information from hierarchical windows. Extensive experiments verify the effectiveness and efficiency of our HiT-SR, and our improved versions of SwinIR-Light, SwinIR-NG, and SRFormer-Light yield state-of-the-art SR results with fewer parameters, FLOPs, and faster speeds (~7x).

📑 Contents

• 🛠️Setup
• 💿Datasets
• 🚀Models
• 🏋Training
• 🧪Testing
• 📊Results
• 📎Citation
• 🏅Acknowledgements

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🛠️ Setup

• Python 3.8
• PyTorch 1.8.0 + Torchvision 0.9.0
• NVIDIA GPU + CUDA

git clone https://github.com/XiangZ-0/HiT-SR.git
conda create -n HiTSR python=3.8
conda activate HiTSR
pip install -r requirements.txt
python setup.py develop

💿 Datasets

Training and testing sets can be downloaded as follows:

Training Set	Testing Set	Visual Results
DIV2K (800 training images, 100 validation images) [organized training dataset DIV2K: One Drive]	Set5 + Set14 + BSD100 + Urban100 + Manga109 [complete testing dataset: One Drive]	One Drive

Download training and testing datasets and put them into the corresponding folders of datasets/. See datasets for the detail of the directory structure.

🚀 Models

Method	#Param. (K)	FLOPs (G)	Dataset	PSNR (dB)	SSIM	Model Zoo	Visual Results
HiT-SIR	792	53.8	Urban100 (x4)	26.71	0.8045	One Drive	One Drive
HiT-SNG	1032	57.7	Urban100 (x4)	26.75	0.8053	One Drive	One Drive
HiT-SRF	866	58.0	Urban100 (x4)	26.80	0.8069	One Drive	One Drive

The output size is set to 1280x720 to compute FLOPs.

🏋 Training

• Download training (DIV2K, already processed) and testing (Set5, Set14, BSD100, Urban100, Manga109, already processed) datasets, place them in datasets/.

• Run the following scripts. The training configuration is in options/Train/.

  # HiT-SIR, input=64x64, 4 GPUs
  python -m torch.distributed.launch --nproc_per_node=4 --master_port=1234 basicsr/train.py -opt options/Train/train_HiT_SIR_x2.yml --launcher pytorch
  python -m torch.distributed.launch --nproc_per_node=4 --master_port=1234 basicsr/train.py -opt options/Train/train_HiT_SIR_x3.yml --launcher pytorch
  python -m torch.distributed.launch --nproc_per_node=4 --master_port=1234 basicsr/train.py -opt options/Train/train_HiT_SIR_x4.yml --launcher pytorch
  
  # HiT-SNG, input=64x64, 4 GPUs
  python -m torch.distributed.launch --nproc_per_node=4 --master_port=4321 basicsr/train.py -opt options/Train/train_HiT_SNG_x2.yml --launcher pytorch
  python -m torch.distributed.launch --nproc_per_node=4 --master_port=4321 basicsr/train.py -opt options/Train/train_HiT_SNG_x3.yml --launcher pytorch
  python -m torch.distributed.launch --nproc_per_node=4 --master_port=4321 basicsr/train.py -opt options/Train/train_HiT_SNG_x4.yml --launcher pytorch
  
  # HiT-SRF, input=64x64, 4 GPUs
  python -m torch.distributed.launch --nproc_per_node=4 --master_port=1234 basicsr/train.py -opt options/Train/train_HiT_SRF_x2.yml --launcher pytorch
  python -m torch.distributed.launch --nproc_per_node=4 --master_port=1234 basicsr/train.py -opt options/Train/train_HiT_SRF_x3.yml --launcher pytorch
  python -m torch.distributed.launch --nproc_per_node=4 --master_port=1234 basicsr/train.py -opt options/Train/train_HiT_SRF_x4.yml --launcher pytorch

• The training experiments will be stored in experiments/.

🧪 Testing

Test with ground-truth images

• Download the pre-trained models and place them in experiments/pretrained_models/.

  We provide pre-trained models for efficient image SR: HiT-SIR, HiT-SNG, and HiT-SRF (x2, x3, x4).

• Download testing datasets (Set5, Set14, BSD100, Urban100, Manga109), place them in datasets/.

• Run the following scripts. The testing configuration is in options/Test/ (e.g., test_HiT_SIR_x2.yml).

  Note 1: You can set use_chop: True (default: False) in YML to chop the image for testing.

  # No self-ensemble
  # HiT-SIR, reproduces results in Table 2 of the main paper
  python basicsr/test.py -opt options/Test/test_HiT_SIR_x2.yml
  python basicsr/test.py -opt options/Test/test_HiT_SIR_x3.yml
  python basicsr/test.py -opt options/Test/test_HiT_SIR_x4.yml
  
  # HiT-SNG, reproduces results in Table 2 of the main paper
  python basicsr/test.py -opt options/Test/test_HiT_SNG_x2.yml
  python basicsr/test.py -opt options/Test/test_HiT_SNG_x3.yml
  python basicsr/test.py -opt options/Test/test_HiT_SNG_x4.yml
  
  # HiT-SRF, reproduces results in Table 2 of the main paper
  python basicsr/test.py -opt options/Test/test_HiT_SRF_x2.yml
  python basicsr/test.py -opt options/Test/test_HiT_SRF_x3.yml
  python basicsr/test.py -opt options/Test/test_HiT_SRF_x4.yml

• The output is stored in results/. All visual results of our pre-trained models can be accessed via one drive.

Test without ground-truth images

• Download the pre-trained models and place them in experiments/pretrained_models/.

  We provide pre-trained models for efficient image SR: HiT-SIR, HiT-SNG, and HiT-SRF (x2, x3, x4).

• Put your dataset (single LR images) in datasets/single. Some example images are in this folder.

• Run the following scripts. The testing configuration is in options/test/ (e.g., test_single_x2.yml).

  Note 1: The default model is HiT-SRF. You can use other models like HiT-SIR by modifying the YML.

  Note 2: You can set use_chop: True (default: False) in YML to chop the image for testing.

  # Test on your dataset without ground-truth images
  python basicsr/test.py -opt options/Test/test_single_x2.yml
  python basicsr/test.py -opt options/Test/test_single_x3.yml
  python basicsr/test.py -opt options/Test/test_single_x4.yml

• The output is stored in results/.

📊 Results

We apply our HiT-SR approach to improve SwinIR-Light, SwinIR-NG and SRFormer-Light, corresponding to our HiT-SIR, HiT-SNG, and HiT-SRF. Compared with the original structure, our improved models achieve better SR performance while reducing computational burdens.

• Performance improvements of HiT-SR (SIR, SNG, and SRF indicate SwinIR-Light, SwinIR-NG, and SRFormer-Light, respectively).

• Efficiency improvements of HiT-SR (SIR, SNG, and SRF indicate SwinIR-Light, SwinIR-NG, and SRFormer-Light, respectively). The complexity metrics are calculated under x2 upscaling on an A100 GPU, with the output size set to 1280x720.

• Overall improvements of HiT-SR

• Convergence improvements of HiT-SR

More detailed results can be found in the paper. All visual results of can be downloaded here.

More results (click to expan)

• Quantitative comparison

• Local attribution map (LAM) comparison (more marked pixels indicate better information aggragation ability)

• Qualitative comparison on challenging scenes

📎 Citation

If you find the code helpful in your research or work, please consider citing the following paper.

@inproceedings{zhang2024hitsr,
    title={HiT-SR: Hierarchical Transformer for Efficient Image Super-Resolution},
    author={Zhang, Xiang and Zhang, Yulun and Yu, Fisher},
    booktitle={ECCV},
    year={2024}
}

🏅 Acknowledgements

This project is built on DAT, SwinIR, NGramSwin, SRFormer, and BasicSR. Special thanks to their excellent works!