Change Point Detection (CPD) refers to the task of identifying abrupt changes in the characteristics or statistics of time series data. Recent advancements have led to a shift away from traditional model-based CPD approaches, which rely on predefined statistical distributions, toward neural network-based and distribution-free methods using autoencoders. However, many state-of-the-art methods in this category often neglect to explicitly leverage spatial information across multiple channels, making them less effective at detecting changes in cross-channel statistics. In this paper, we introduce an unsupervised, distribution-free CPD method that explicitly incorporates both temporal and spatial (cross-channel) information in multi-channel time series data based on the so-called Time-Invariant Representation (TIRE) autoencoder. Our evaluation, conducted on both simulated and real-life datasets, illustrates the significant advantages of our proposed multi-channel TIRE (MC-TIRE) method, which consistently delivers more accurate CPD results.

Change point detection (CPD) refers to the problem of detecting changes in the statistics of pseudo-stationary signals or time series. A recent trend in CPD research is to replace the traditional statistical tests with distribution-free autoencoder-based algorithms, which can automatically learn complex patterns in time series data. In particular, the so-called time-invariant representation (TIRE) models have gained traction, as these separately encode time-variant and time-invariant subfeatures, as opposed to traditional autoencoders. However, optimizing the trade-off between two loss terms, i.e., the reconstruction loss and the time-invariant loss, is challenging. To address this issue, we propose a novel loss function that elegantly combines both losses without the need for manually tuning a trade-off hyperparameter. We demonstrate that this new hyperparameter-free loss, in combination with a relatively simple convolutional neural network (CNN), consistently achieves superior or comparable performance compared to the manually-tuned baseline TIRE models across diverse benchmark datasets, both simulated and real-life. In addition, we present a representation analysis, demonstrating that the distribution of the time-invariant features extracted by our model is more concentrated within the same segment (more so than with previous TIRE models), which implies that these features can potentially be used for other applications, such as classification and clustering.

Typical approaches for video face recognition aggregate faces in a feature space to obtain a single feature representing the entire video. Unlike most previous approaches, we aggregate the faces directly in order to additionally obtain a single representative face as an intermediate output, from which a more discriminative feature vector is extracted. To overcome the limitation of a fixed number of input images of the state of the art in face aggregation, we incorporate a permutation invariant U-Net architecture capable of processing an arbitrary number of frames, which is employed in a generative adversarial network. We demonstrate the effectiveness of our method on three popular benchmark datasets for video face recognition. Our approach outperforms the baselines on the YouTube Faces dataset, obtaining an accuracy of 96.62%. Besides, we show that our method is robust against motion blur.