Unsupervised learning; Dimensionality reduction; PCA; F-transform; Image classification; Autoencoder

We focus on an image classification task in which only several unlabeled images per class are available for learning and low computational complexity is required. We recall the state-of-the-art methods that are used to solve the task: autoencoder-based approaches and manifold-decomposition-based approaches. Next, we introduce our proposed method, which is based on a combination of the F-transform and (kernel) principal component analysis. F-transform significantly reduces the computation time of PCA and increases the robustness of PCA to translation, while PCA proposes more descriptive features. This combination performs 3D reduction: the F-transform reduces dimensionality over a single 2D image, while PCA reduces dimensionality through the whole set of processed images. Based on the benchmark results, our method may outperform deep-learning-based methods in limited settings. For completeness, we also address other image resampling algorithms that can be used instead of the F-transform, and we find that the F-transform is the most suitable.