Image BERT Pre-Training with iBOT

Official PyTorch implementation and pre-trained models for paper iBOT: Image BERT Pre-Training with Online Tokenizer.

[arXiv] [Colab] [BibTex]

iBOT is a novel self-supervised pre-training framework that performs masked image modeling with self-distillation. iBOT pre-trained model shows local semantic features, which helps the model transfer well to downstream tasks both at a global scale and a local scale. For example, iBOT achieves strong performance on COCO object detection (51.2 box AP and 44.2 mask AP) and ADE20K semantic segmentation (50.0 mIoU) with vanilla ViT-B/16. iBOT can also extract semantic-meaningful local parts, like dog's ear 🐶.

News 🎉

• January 2022 - The paper is accepted by ICLR 2022.
• Update - ViT-L/16 with ImageNet-1K pre-training achieves 81.0% in linear probing accuracy. ViT-L/16 with ImageNet-22K pre-training achieves 87.8% in 512x fine-tuning accuracy.
• Update - Random masking with a relatively larger prediction ratio performs slighly better than block-wise masking. For example, ViT-B/16 achieves an 84.1% fine-tuning accuracy and a 51.5 box AP in object detection.
• December 2021 - Release the code and pre-trained models.
• November 2021 - Release the pre-print on arXiv.

Installation

See installation structions for details.

One-Line Command by Using run.sh

We provide run.sh with which you can complete the pre-training + fine-tuning experiment cycle in an one-line command.

Arguments

• TYPE is named by the rule of dataset_task. For example, pre-training on ImageNet-1K has a TYPE of imagenet_pretrain and linear probing evalution on ImageNet-1K has a TYPE of imagenet_linear. Different types of task can be appended in one command.
• JOB_NAME is the customized job name to distinguish from different groups of experiments.
• ARCH is the architecture of the pre-trained models.
• KEY chooses which pre-trained model to be evaluated and can be set as either teacher (generally better) or student for one model.
• GPUS is GPUs needed for each node, and will be clamped by MAX_GPUS (default as 8).
• Other additional arguments can directly appended after these required ones. For example, --lr 0.001.

For example, the following command will automatically evaluate the models on K-NN and linear probing benchmark after the pre-training with student and teacher model distributed across 2 nodes:

TOTAL_NODES=2 NODE_ID=0 ./run.sh imagenet_pretrain+imagenet_knn+imagenet_linear vit_small student,teacher 16 // the first node
TOTAL_NODES=2 NODE_ID=1 ./run.sh imagenet_pretrain+imagenet_knn+imagenet_linear vit_small student,teacher 16 // the second node

Training

For a glimpse at the full documentation of iBOT pre-training, please run:

python main_ibot.py --help

iBOT Pre-Training with ViTs

To start the iBOT pre-training with Vision Transformer (ViT), simply run the following commands. JOB_NAME is a customized argument to distinguish different experiments and this will automatically save checkpoints into the seperate folders.

./run.sh imagenet_pretrain $JOB_NAME vit_{small,base,large} teacher {16,24,64}

The exact arguments to reproduce the models presented in our paper can be found in the args column of the pre-trained models. We also provide the logs for pre-training to help reproducibility.

For example, run iBOT with ViT-S/16 network on two nodes with 8 GPUs for 800 epochs with the following command. The resulting checkpoint should reach 75.2% on k-NN accuracy, 77.9% on linear probing accuracy, and 82.3% on fine-tuning accuracy.

./run.sh imagenet_pretrain $JOB_NAME vit_small teacher 16 \
  --teacher_temp 0.07 \
  --warmup_teacher_temp_epochs 30 \
  --norm_last_layer false \
  --epochs 800 \
  --batch_size_per_gpu 64 \
  --shared_head true \
  --out_dim 8192 \
  --local_crops_number 10 \
  --global_crops_scale 0.25 1 \
  --local_crops_scale 0.05 0.25 \
  --pred_ratio 0 0.3 \
  --pred_ratio_var 0 0.2

iBOT Pre-Training with Swins

This code also works for training iBOT on Swin Transformer (Swin). In the paper, we only conduct experiments on Swin-T with different window sizes:

./run.sh imagenet_pretrain $JOB_NAME swin_tiny teacher {16,40} \
  --patch_size 4 \
  --window_size {7,14}

For example, run iBOT with Swin-T/14 network on five nodes with 8 GPUS for 300 epochs with the following command. The resulting checkpoint should reach 76.2% on k-NN accuracy, 79.3% on linear probing accuracy.

./run.sh imagenet_pretrain $JOB_NAME swin_tiny teacher 40 \
  --teacher_temp 0.07 \
  --warmup_teacher_temp_epochs 30 \
  --norm_last_layer false \
  --epochs 300 \
  --batch_size_per_gpu 26 \
  --shared_head true \
  --out_dim 8192 \
  --local_crops_number 10 \
  --global_crops_scale 0.25 1 \
  --local_crops_scale 0.05 0.25 \
  --pred_ratio 0 0.3 \
  --pred_ratio_var 0 0.2 \
  --pred_start_epoch 50 \
  --patch_size 4 \
  --window_size 14 

Pre-Trained Models

You can choose to download only the weights of the pre-trained backbone used for downstream tasks, and the full ckpt which contains backbone and projection head weights for both student and teacher networks. For the backbone, s denotes that the student network is selected while t denotes that the teacher network is selected. PS denotes prediction shape.

We also provide the ViT-{B,L}/16 model pre-trained on ImageNet-22K dataset.

To extract the backbone from the full checkpoint by yourself, please run the following command where KEY being either student or teacher.

WEIGHT_FILE=$OUTPUT_DIR/checkpoint_$KEY.pth

python extract_backbone_weights.py \
  --checkpoint_key $KEY \
  $PRETRAINED \
  $WEIGHT_FILE \

Downstream Evaluation

See Evaluating iBOT on Downstream Tasks for details.

Property Analysis

See Analyzing iBOT's Properties for robustness test and visualizing self-attention map:

or extracting sparse correspondence pairs between two images:

We also provide a Colab page 📑 you can play around with iBOT pre-trained models.

Extracting Semantic Patterns

We extract top-k numbered local classes based on patch tokens with their corresponding patches and contexts by running the following command. We indentify very diverse behaviour like shared low-level textures and high-level semantics.

python3 -m torch.distributed.launch --nproc_per_node=8 \
    --master_port=${MASTER_PORT:-29500} \
    analysis/extract_pattern/extract_topk_cluster.py \
    --pretrained_path $PRETRAINED \
    --checkpoint {student,teacher} \
    --type patch \
    --topk 36 \
    --patch_window 5 \
    --show_pics 20 \
    --arch vit_small \
    --save_path memory_bank_patch.pth \
    --data_path data/imagenet/val

The script also supports to extract the patern layout on the [CLS] token, which is actually doing clustering or unsupervised classification. This property is not induced by MIM objective since we also spot this feature on DINO.

python3 -m torch.distributed.launch --nproc_per_node=8 \
    --master_port=${MASTER_PORT:-29500} \
    analysis/extract_pattern/extract_topk_cluster.py \
    --pretrained_path $PRETRAINED \
    --checkpoint {student,teacher} \
    --type cls \
    --topk 36 \
    --show_pics 20 \
    --arch vit_small \
    --save_path memory_bank_cls.pth \
    --data_path data/imagenet/val

Acknowledgement

This repository is built using the DINO repository and the BEiT repository.

License

This repository is released under the Apache 2.0 license as found in the LICENSE file.

Citing iBOT

If you find this repository useful, please consider giving a star ⭐ and citation:

@article{zhou2021ibot,
  title={iBOT: Image BERT Pre-Training with Online Tokenizer},
  author={Zhou, Jinghao and Wei, Chen and Wang, Huiyu and Shen, Wei and Xie, Cihang and Yuille, Alan and Kong, Tao},
  journal={International Conference on Learning Representations (ICLR)},
  year={2022}
}