Contrastive Learning Improves Model Robustness Under Label Noise

This is an official repository of the paper Contrastive Learning Improves Model Robustness Under Label Noise to be presented at Learning from Limited or Imperfect Data (L^2ID) Workshop @ CVPR 2021.

In this paper, we show that by initializing supervised robust methods using representations learned through contrastive learning leads to significantly improved performance under label noise. Surprisingly, even the simplest method (training a classifier with the CCE loss) can outperform the state-of-the-art SSL method by more than 50% under high label noise when initialized with contrastive learning.

Here is a snippet of the experimental results on CIFAR datasets under symmetric label noise.

Environment Setup

This repository uses the following packages in Python3.

torch==1.7.1
torchvision==0.8.2
higher==0.2.1

Training

You can download the pre-trained models from Onedrive.

The pretrained.zip file contains three SimCLR pre-trained models for CIFAR-10, CIFAR-100, and Clothing1M dataset. These models are trained using this excellent Pytorch implementation for SimCLR. The pretrained.zip file also contains the configs for training those models. Note, input to the SimCLR model were not normalized

The pretrained.zip file also contains an ImageNet32 pre-trained model on ResNet-50 architecture (with changing the first conv layer of kernel size 7 with a kernel size of 3 and removing the first max-pool operation.) Alternatively, you can run imagenet32.py on ImageNet32 dataset This ImageNet32 pre-trained model was used to initialize for CIFAR datasets. For the clothing1M dataset, directly use PyTorch pre-trained ImageNet model. ImageNet pre-trained initialization expects normalized inputs.

I added configs file for the three datasets in config/ folder. Unzip pretrained.zip in ../ folder. Run,

python train.py\
    --config config/<name of datasets>.yaml\
    --corruption_prob {corruption_prob}\ 
    --corruption_type {corruption_type}\ 
    --encoder_type {encoder_type: imagenet or simclr}\
    --problem {problem: mwnet or finetune}\
    --loss {loss: ce or qloss}\
    --q {q}\
    --seed {seed}\
    --neptune --cuda 

To run with the CCE loss or generalized cross-entropy loss, use --loss ce or --loss qloss and --problem finetune. For meta-weight-net use --loss ce and --problem mwnet. For parameter ranges, check the scheduler.py file.

MetaWeight Network implementation

I simplified the official implementation using higher package. You can use any architecture without needing to write separate custom meta modules.

There are a couple of differences with the official implementation; however, you can simply change these to follow the original code from the author.

• Line 351 in models/noisy_models.py, I am using a constant inner learning rate (instead of the classifier learning rate).
• Line 377 in models/noisy_models.py, I am using the sum of the weighted loss for the meta samples (instead of normalized weighted loss).
• You can try with other loss functions for the meta samples; I added MAE loss in Line 366 in models/noisy_models.py as they are shown to be superior without the need for clean meta samples, in this paper

Generalized Cross-entropy loss implementation

I do not use the truncated version of the generalized cross-entropy loss. Instead, the generalized cross-entropy loss is applied directly; and they perform remarkably well with the right initializer (otherwise, not so much!).

Attribution

Parts of this code are based on the following repositories:

• SimCLR PyTorch, PyTorch Lightning for standard backbones, training loops, and SimCLR model training.
• Meta-Weight-Net: Learning an Explicit Mapping For Sample Weighting (Official Pytorch implementation for noisy labels for the original implementation of MetaWeight Network.
• Higher Package is used to simplify the Metaweight network implementation.

Citation

If you find this code useful in your research then please cite

@InProceedings{Ghosh_2021_CVPR_Workshops,
author    = {Ghosh, Aritra and Lan, Andrew},
title = {Contrastive Learning Improves Model Robustness Under Label Noise},
booktitle = {Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR) Workshops},
year = {2021}
}

Contact: Aritra Ghosh (aritraghosh.iem@gmail.com).