  In this paper, we propose the Generalized Parametric Contrastive Learning
(GPaCo/PaCo) which works well on both imbalanced and balanced data. Based on
theoretical analysis, we observe that supervised contrastive loss tends to bias
high-frequency classes and thus increases the difficulty of imbalanced
learning. We introduce a set of parametric class-wise learnable centers to
rebalance from an optimization perspective. Further, we analyze our GPaCo/PaCo
loss under a balanced setting. Our analysis demonstrates that GPaCo/PaCo can
adaptively enhance the intensity of pushing samples of the same class close as
more samples are pulled together with their corresponding centers and benefit
hard example learning. Experiments on long-tailed benchmarks manifest the new
state-of-the-art for long-tailed recognition. On full ImageNet, models from
CNNs to vision transformers trained with GPaCo loss show better generalization
performance and stronger robustness compared with MAE models. Moreover, GPaCo
can be applied to the semantic segmentation task and obvious improvements are
observed on the 4 most popular benchmarks. Our code is available at
https://github.com/dvlab-research/Parametric-Contrastive-Learning.
