  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.
