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In this paper, a novel algorithm for non-parametric image clustering, is proposed. Nonparametric clustering methods operate by considering the number of clusters unknown as opposed to parametric clustering, where the number of clusters is known a priori. In the present work, a deep neural network is trained, in order to decide whether an arbitrary sized group of elements can be considered as a unique cluster or it consists of more than one clusters. Using this trained neural network as clustering criterion, an iterative algorithm is built, able to cluster any given dataset. Evaluation of the proposed method on several public datasets shows that the proposed method is either on par or outperforms stateof-the-art methods even when compared to parametric image clustering methods. The proposed method is additionally able to correctly cluster input samples from a completely different dataset than the one it has been trained on, as well as data coming from different modalities. Results on cross-dataset clustering show evidence of the generalization potential of the proposed method.

The undeniable computational power of artificial neural networks has granted the scientific community the ability to exploit the available data in ways previously inconceivable. However, deep neural networks require an overwhelming quantity of data in order to interpret the underlying connections between them, and therefore, be able to complete the specific task that they have been assigned to. Feeding a deep neural network with vast amounts of data usually ensures efficiency, but may, however, harm the network’s ability to generalize. To tackle this, numerous regularization techniques have been proposed, with dropout being one of the most dominant. This paper proposes a selective gradient dropout method, which, instead of relying on dropping random weights, learns to freeze the training process of specific connections, thereby increasing the overall network’s sparsity in an adaptive manner, by driving it to utilize more salient weights. The experimental results show that the produced sparse network outperforms the baseline on numerous image classification datasets, and additionally, the yielded results occurred after significantly less training epochs.