In supervised learning, smoothing label or prediction distribution in neural network training has been proven useful in preventing the model from being over-confident, and is crucial for learning more robust visual representations. This observation motivates us to explore ways to make predictions flattened in unsupervised learning. Considering that human-annotated labels are not adopted in unsupervised learning, we introduce a straightforward approach to perturb input image space in order to soften the output prediction space indirectly, meanwhile, assigning new label values in the unsupervised frameworks accordingly. Despite its conceptual simplicity, we show empirically that with the simple solution -- Unsupervised image mixtures (Un-Mix), we can learn more robust visual representations from the transformed input. Extensive experiments are conducted on CIFAR-10, CIFAR-100, STL-10, Tiny ImageNet and standard ImageNet with popular unsupervised methods SimCLR, BYOL, MoCo V1&V2, etc. Our proposed image mixture and label assignment strategy can obtain consistent improvement by 1~3% following exactly the same hyperparameters and training procedures of the base methods.
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