This paper proposes a comprehensive method for online-event clustering in videos. Adaptive Gaussian mixture of foreground and they were modelled using the time series modelling technique. A cross-substitution based model comparison method was employed to compare the disparity between events. Spectral clustering (SC) was utilised to cluster events, and methods for SC initial parameter selection have been proposed. A method for cluster identity assignment in consecutive clustering iterations is also utilised to handle the evolving nature of the unsupervised learning methodology adopted. The proposed method is capable of producing reliable clustering results online, amidst a number of complications including dynamic backgrounds, object shadows, camera distortions, sudden foreground bursts and inter-object interactions.Event clustering, foreground estimation, trajectory modelling.
INTRODUCTIONHumans are capable of identifying similarities and dissimilarities between the events they perceive. The objective of event clustering is to produce a set of event clusters to follow human heuristics through an automated process. Such systems are widely applied in (Gowsikhaa et al., 2014), bio vision applications (Jiang et al., 2013; Aqel et al., 2016) and abnormal event detection (Archetti et al., 2006 ; Guo et al., 2013;Ranjith et al., 2015). of activities performed by an object (Porikli & Haga, 2004;Utsumi et al., 2013). An event is described using a set of temporal features of the relevant object such as its location, velocity and size. Therefore, obtaining various feature variations of objects under consideration becomes one of the primary exercises in event clustering. In order to construct the necessary feature space, the desired foreground objects need to be segmented and tracked throughout the video. Therefore, any event detection practice comprises a series of sub processes, namely, foreground estimation, construction and clustering. The paper proposes a comprehensive methodology, which addresses each of these sub processes in a sequential manner to arrive at a robust event clustering system. Most of the previously proposed foreground estimation methods utilise the principle of background subtraction (Zang & Klette, 2004;Qin et al., 2013). Employment of a single background has long gone obsolete due to its inability to capture gradual changes in the background. Rahman et al. (2010) and Yang et al. (2005) have proposed remedies to absorb the background illumination change into the background reference model. But both these methods are ineffective when external objects are introduced to the background. The method proposed in Stauffer and Grimson (2000) is capable of tackling the issue of gradual background changes by modelling each pixel as a mixture of Gaussian distributions.