Robust fine-tuning of zero-shot models

This repository contains code for the paper Robust fine-tuning of zero-shot models by Mitchell Wortsman*, Gabriel Ilharco*, Jong Wook Kim, Mike Li, Simon Kornblith, Rebecca Roelofs, Raphael Gontijo-Lopes, Hannaneh Hajishirzi, Ali Farhadi, Hongseok Namkoong, Ludwig Schmidt.

Abstract

Large pre-trained models such as CLIP offer consistent accuracy across a range of data distributions when performing zero-shot inference (i.e., without fine-tuning on a specific dataset). Although existing fine-tuning approaches substantially improve accuracy in-distribution, they also reduce out-of-distribution robustness. We address this tension by introducing a simple and effective method for improving robustness: ensembling the weights of the zero-shot and fine-tuned models. Compared to standard fine-tuning, the resulting weight-space ensembles provide large accuracy improvements out-of-distribution, while matching or improving in-distribution accuracy. On ImageNet and five derived distribution shifts, weight-space ensembles improve out-of-distribution accuracy by 2 to 10 percentage points while increasing in-distribution accuracy by nearly 1 percentage point relative to standard fine-tuning. These improvements come at no additional computational cost during fine-tuning or inference.

Summary figure

Compared to standard fine-tuning, weight-space ensembles for fine-tuning (WiSE-FT) improve out-of-distribution (OOD) accuracy without decreasing in-distribution (ID) performance. Top left: Zero-shot CLIP models exhibit high effective robustness and moderate in-distribution accuracy, while standard fine-tuning (end-to-end or with a linear classifier) attains higher ID accuracy and less effective robustness. Top right: Our method linearly interpolates between the zero-shot and fine-tuned models with a mixing coefficient alpha in [0,1]. Bottom: On five distribution shifts derived from ImageNet (ImageNetV2, ImageNet-R, ImageNet Sketch, ObjectNet, and ImageNet-A), WiSE-FT improves average OOD accuracy by 8.7 percentage points (pp) when fine-tuning end-to-end (+2.1 pp when fine-tuning a linear classifier) while maintaining ID accuracy.

Code

Overview

WiSE-FT can be implemented in a few lines of code in addition to standard fine-tuning, as shown below. See src/wise_ft.py for more details.

# Load models
zeroshot = ImageClassifier.load(zeroshot_checkpoint)
finetuned = ImageClassifier.load(finetuned_checkpoint)
theta_0 = zeroshot.state_dict()
theta_1 = finetuned.state_dict()

# make sure checkpoints are compatible
assert set(theta_0.keys()) == set(theta_1.keys())

# interpolate between checkpoints with mixing coefficient alpha
theta = {
    key: (1-alpha) * theta_0[key] + alpha * theta_1[key]
    for key in theta_0.keys()
}

# update the model acccording to the new weights
finetuned.load_state_dict(theta)

# evaluate
evaluate(finetuned, args)

Install dependencies

conda env create
conda activate wiseft

Add directory to PYTHONPATH:

cd wise-ft
export PYTHONPATH="$PYTHONPATH:$PWD"

Download data

When necessary, please refer to datasets.md for instructions on how to download datasets.

Run WiSE-FT

Sample command when zeroshot and fine-tuned models are available:

python src/wise_ft.py   \
    --eval-datasets=ImageNet,ImageNetV2,ImageNetR,ImageNetA,ImageNetSketch  \
    --load=models/zeroshot.pt,models/finetuned.pt  \
    --results-db=results.jsonl  \
    --save=models/wiseft  \
    --data-location=~/data \
    --alpha 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Sample command for running WiSE-FT from scratch using ViT-B/32:

python src/wise_ft.py   \
    --train-dataset=ImageNet  \
    --epochs=10  \
    --lr=0.00003  \
    --batch-size=512  \
    --cache-dir=cache  \
    --model=ViT-B/32  \
    --eval-datasets=ImageNet,ImageNetV2,ImageNetR,ImageNetA,ImageNetSketch  \
    --template=openai_imagenet_template  \
    --results-db=results.jsonl  \
    --save=models/wiseft/ViTB32  \
    --data-location=~/data \
    --alpha 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Note: the flag --freeze-encoder controls whether only a linear classifier is fine-tuned, or if all weights are fine-tuned (end-to-end).

Plotting results

Sample command for generating a scatter plot:

python src/scatter_plot.py  \
    --eval-datasets=ImageNetV2,ImageNetR,ImageNetA,ImageNetSketch  \
    --results-db=results.jsonl  \
    --save plots

We show samples of expected behavior below when running the commands above using ViT-B/16 (models can be downloaded here):

Citing

If you found this repository useful, please consider citing:

@article{wortsman2021robust,
  title={Robust fine-tuning of zero-shot models},
  author={Wortsman, Mitchell and Ilharco, Gabriel and Kim, Jong Wook and Li, Mike and Kornblith, Simon and Roelofs, Rebecca and Gontijo-Lopes, Raphael and Hajishirzi, Hannaneh and Farhadi, Ali and Namkoong, Hongseok and Schmidt, Ludwig},
  journal={arXiv preprint arXiv:2109.01903},
  note={\url{https://arxiv.org/abs/2109.01903}},
  year={2021}
}