Title: "Change and Anomaly Detection by Means of Sparse Representations"

Abstract:
Sparse representations are one of the most important models in signal/image processing. Sparse models have been originally introduced for descriptive tasks -- denoising/regression --, while more recently also discriminative tasks -- and in particular classification -- have been addressed in the sparse representation literature. During this talk, I will present our works in the direction of exploiting sparse representation for change/anomaly detection, namely, the identification of data departing from the normal (stationary) conditions. We assume that normal data admits a sparse representation w.r.t. a suitable dictionary, thus that they are well approximated in a union of low-dimensional subspaces. Performing change/anomaly detection then corresponds to identifying data that departs from these subspaces, both because of a permanent shift in the data-generating process (change-detection) or because of a sporadic event (anomaly detection).
I will illustrate the effectiveness of sparse representations for performing change/anomaly detection in two application scenarios. The first one consists in an environmental monitoring application, where nodes of a sensor network deployed over a rock face acquires acoustic emissions (bursts). The stream of bursts is then analyzed to detect structural changes which might be associated with macroscopic variation in the monitored phenomenon, eventually leading to a rock collapse. The second one consists in an industrial monitoring application, where a scanning electron microscope (SEM) is used to supervise the production of nanofibres. Here, we address the problem of detecting anomalous patterns in the acquired images, which might indicate a degradation in the quality of the produced materials.

Reference Works

Cesare Alippi, Giacomo Boracchi, Brendt Wohlberg: "Change Detection in Streams of Signals with Sparse Representations" ICASSP 2014 , IEEE International Conference on Acoustics, Speech and Signal Processing, Florence, Italy, May 4 - 9, pp 5252 - 5256 doi:10.1109/ICASSP.2014.6854605 
Preprint available at http://home.deib.polimi.it/boracchi/docs/2014_03_Sparsity-based_CDT_ICASSP.pdf 

Giacomo Boracchi, Diego Carrera, Brendt Wohlberg: "Anomaly Detection in Images by Sparse Representations", Submitted to Intelligent Embedded System Symposium, IEEE SSCI 2014 
Preprint available at http://home.deib.polimi.it/boracchi/docs/2014_09_NoveltyDetectionSparseRepresentations_IES14.pdf