Unsupervised Learning of Visual Features by Contrasting Cluster Assignments

TL;DR

This paper introduces SwAV, an efficient unsupervised learning method that clusters data and enforces consistency between different views of images, achieving high accuracy without pairwise comparisons.

Contribution

SwAV presents a novel online clustering approach for unsupervised visual representation learning that is scalable, memory-efficient, and surpasses previous contrastive methods.

Findings

Achieves 75.3% top-1 accuracy on ImageNet with ResNet-50.

Outperforms supervised pretraining on multiple transfer tasks.

Introduces multi-crop data augmentation strategy.

Abstract

Unsupervised image representations have significantly reduced the gap with supervised pretraining, notably with the recent achievements of contrastive learning methods. These contrastive methods typically work online and rely on a large number of explicit pairwise feature comparisons, which is computationally challenging. In this paper, we propose an online algorithm, SwAV, that takes advantage of contrastive methods without requiring to compute pairwise comparisons. Specifically, our method simultaneously clusters the data while enforcing consistency between cluster assignments produced for different augmentations (or views) of the same image, instead of comparing features directly as in contrastive learning. Simply put, we use a swapped prediction mechanism where we predict the cluster assignment of a view from the representation of another view. Our method can be trained with large and small batches and can scale to unlimited amounts of data. Compared to previous contrastive methods, our method is more memory efficient since it does not require a large memory bank or a special momentum network. In addition, we also propose a new data augmentation strategy, multi-crop, that uses a mix of views with different resolutions in place of two full-resolution views, without increasing the memory or compute requirements much. We validate our findings by achieving 75.3% top-1 accuracy on ImageNet with ResNet-50, as well as surpassing supervised pretraining on all the considered transfer tasks.