Vision Transformer for Contrastive Clustering

Vision Transformer (ViT) has shown its advantages over the convolutional neural network (CNN) with its ability to capture global long-range dependencies for visual representation learning. Besides ViT, contrastive learning is another popular research topic recently. While previous contrastive learning works are mostly based on CNNs, some latest studies have attempted to jointly model the ViT and the contrastive learning for enhanced self-supervised learning. Despite the considerable progress, these combinations of ViT and contrastive learning mostly focus on the instance-level contrastiveness, which often overlook the contrastiveness of the global clustering structures and also lack the ability to directly learn the clustering result (e.g., for images). In view of this, this paper presents an end-to-end deep image clustering approach termed Vision Transformer for Contrastive Clustering (VTCC), which for the first time, to the best of our knowledge, unifies the Transformer and the contrastive learning for the image clustering task. Specifically, with two random augmentations performed on each image in a mini-batch, we utilize a ViT encoder with two weight-sharing views as the backbone to learn the representations for the augmented samples. To remedy the potential instability of the ViT, we incorporate a convolutional stem, which uses multiple stacked small convolutions instead of a big convolution in the patch projection layer, to split each augmented sample into a sequence of patches. With representations learned via the backbone, an instance projector and a cluster projector are further utilized for the instance-level contrastive learning and the global clustering structure learning, respectively. Extensive experiments on eight image datasets demonstrate the stability (during the training-from-scratch) and the superiority (in clustering performance) of VTCC over the state-of-the-art.