Title: Contrastive Hierarchical Clustering. Abstract: Deep clustering has been dominated by flat clustering models, which split a dataset into a predefined number of groups. Although recent methods achieve extremely high similarity with the ground truth on popular benchmarks, the information contained in the flat partition is limited. In this paper, we introduce CoHiClust, a Contrastive Hierarchical Clustering model based on deep neural networks, which can be applied to large-scale image data. By employing a self-supervised learning approach, CoHiClust distills the base network into a binary tree without access to any labeled data. The hierarchical clustering structure can be used to analyze the relationship between clusters as well as to measure the similarity between data points. Experiments performed on typical image benchmarks demonstrate that CoHiClust generates a reasonable structure of clusters, which is consistent with our intuition and image semantics. Moreover, by applying the proposed pruning strategy, we can restrict the hierarchy to the requested number of clusters (leaf nodes) and obtain the clustering accuracy comparable to the state-of-the-art flat clustering baselines.
