dandelin / ViT-pytorch

Pytorch reimplementation of the Vision Transformer (An Image is Worth 16x16 Words: Transformers for Image Recognition at Scale)

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Vision Transformer

Pytorch reimplementation of Google's repository for the ViT model that was released with the paper An Image is Worth 16x16 Words: Transformers for Image Recognition at Scale by Alexey Dosovitskiy, Lucas Beyer, Alexander Kolesnikov, Dirk Weissenborn, Xiaohua Zhai, Thomas Unterthiner, Mostafa Dehghani, Matthias Minderer, Georg Heigold, Sylvain Gelly, Jakob Uszkoreit, Neil Houlsby.

This paper show that Transformers applied directly to image patches and pre-trained on large datasets work really well on image recognition task.

fig1

Vision Transformer achieve State-of-the-Art in image recognition task with standard Transformer encoder and fixed-size patches. In order to perform classification, author use the standard approach of adding an extra learnable "classification token" to the sequence.

fig2

Usage

1. Download Pre-trained model (Google's Official Checkpoint)

  • Available models: ViT-B_16(85.8M), R50+ViT-B_16(97.96M), ViT-B_32(87.5M), ViT-L_16(303.4M), ViT-L_32(305.5M), ViT-H_14(630.8M)
    • imagenet21k pre-train models
      • ViT-B_16, ViT-B_32, ViT-L_16, ViT-L_32, ViT-H_14
    • imagenet21k pre-train + imagenet2012 fine-tuned models
      • ViT-B_16-224, ViT-B_16, ViT-B_32, ViT-L_16-224, ViT-L_16, ViT-L_32
    • Hybrid Model(Resnet50 + Transformer)
      • R50-ViT-B_16
# imagenet21k pre-train
wget https://storage.googleapis.com/vit_models/imagenet21k/{MODEL_NAME}.npz

# imagenet21k pre-train + imagenet2012 fine-tuning
wget https://storage.googleapis.com/vit_models/imagenet21k+imagenet2012/{MODEL_NAME}.npz

2. Train Model

python3 train.py --name cifar10-100_500 --dataset cifar10 --model_type ViT-B_16 --pretrained_dir checkpoint/ViT-B_16.npz

CIFAR-10 and CIFAR-100 are automatically download and train. In order to use a different dataset you need to customize data_utils.py.

The default batch size is 512. When GPU memory is insufficient, you can proceed with training by adjusting the value of --gradient_accumulation_steps.

Also can use Automatic Mixed Precision(Amp) to reduce memory usage and train faster

python3 train.py --name cifar10-100_500 --dataset cifar10 --model_type ViT-B_16 --pretrained_dir checkpoint/ViT-B_16.npz --fp16 --fp16_opt_level O2

Results

To verify that the converted model weight is correct, we simply compare it with the author's experimental results. We trained using mixed precision, and --fp16_opt_level was set to O2.

imagenet-21k

model dataset resolution acc(official) acc(this repo) time
ViT-B_16 CIFAR-10 224x224 - 0.9908 3h 13m
ViT-B_16 CIFAR-10 384x384 0.9903 0.9906 12h 25m
ViT_B_16 CIFAR-100 224x224 - 0.923 3h 9m
ViT_B_16 CIFAR-100 384x384 0.9264 0.9228 12h 31m
R50-ViT-B_16 CIFAR-10 224x224 - 0.9892 4h 23m
R50-ViT-B_16 CIFAR-10 384x384 0.99 0.9904 15h 40m
R50-ViT-B_16 CIFAR-100 224x224 - 0.9231 4h 18m
R50-ViT-B_16 CIFAR-100 384x384 0.9231 0.9197 15h 53m
ViT_L_32 CIFAR-10 224x224 - 0.9903 2h 11m
ViT_L_32 CIFAR-100 224x224 - 0.9276 2h 9m
ViT_H_14 CIFAR-100 224x224 - WIP

imagenet-21k + imagenet2012

model dataset resolution acc
ViT-B_16-224 CIFAR-10 224x224 0.99
ViT_B_16-224 CIFAR-100 224x224 0.9245
ViT-L_32 CIFAR-10 224x224 0.9903
ViT-L_32 CIFAR-100 224x224 0.9285

shorter train

  • In the experiment below, we used a resolution size (224x224).
  • tensorboard
upstream model dataset total_steps /warmup_steps acc(official) acc(this repo)
imagenet21k ViT-B_16 CIFAR-10 500/100 0.9859 0.9859
imagenet21k ViT-B_16 CIFAR-10 1000/100 0.9886 0.9878
imagenet21k ViT-B_16 CIFAR-100 500/100 0.8917 0.9072
imagenet21k ViT-B_16 CIFAR-100 1000/100 0.9115 0.9216

Visualization

The ViT consists of a Standard Transformer Encoder, and the encoder consists of Self-Attention and MLP module. The attention map for the input image can be visualized through the attention score of self-attention.

Visualization code can be found at visualize_attention_map.

fig3

Reference

Citations

@article{dosovitskiy2020,
  title={An Image is Worth 16x16 Words: Transformers for Image Recognition at Scale},
  author={Dosovitskiy, Alexey and Beyer, Lucas and Kolesnikov, Alexander and Weissenborn, Dirk and Zhai, Xiaohua and Unterthiner, Thomas and  Dehghani, Mostafa and Minderer, Matthias and Heigold, Georg and Gelly, Sylvain and Uszkoreit, Jakob and Houlsby, Neil},
  journal={arXiv preprint arXiv:2010.11929},
  year={2020}
}
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Pytorch reimplementation of the Vision Transformer (An Image is Worth 16x16 Words: Transformers for Image Recognition at Scale)

License:MIT License


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