Cultural Event Recognition with Visual ConvNets and Temporal Models

This paper presents our contribution to the ChaLearn Challenge 2015 on Cultural Event Classification. The challenge in this task is to automatically classify images from 50 different cultural events. Our solution is based on the combination of visual features extracted from convolutional neural networks with temporal information using a hierarchical classifier scheme. We extract visual features from the last three fully connected layers of both CaffeNet (pretrained with ImageNet) and our fine tuned version for the ChaLearn challenge. We propose a late fusion strategy that trains a separate low-level SVM on each of the extracted neural codes. The class predictions of the low-level SVMs form the input to a higher level SVM, which gives the final event scores. We achieve our best result by adding a temporal refinement step into our classification scheme, which is applied directly to the output of each low-level SVM. Our approach penalizes high classification scores based on visual features when their time stamp does not match well an event-specific temporal distribution learned from the training and validation data. Our system achieved the second best result in the ChaLearn Challenge 2015 on Cultural Event Classification with a mean average precision of 0.767 on the test set.Comment: Initial version of the paper accepted at the CVPR Workshop ChaLearn Looking at People 201

Detection of Social Events in Streams of Social Multimedia

Combining items from social media streams, such as Flickr photos and Twitter tweets, into meaningful groups can help users contextualise and consume more effectively the torrents of information continuously being made available on the social web. This task is made challenging due to the scale of the streams and the inherently multimodal nature of the information being contextualised.The problem of grouping social media items into meaningful groups can be seen as an ill-posed and application specific unsupervised clustering problem. A fundamental question in multimodal contexts is determining which features best signify that two items should belong to the same grouping.This paper presents a methodology which approaches social event detection as a streaming multi-modal clustering task. The methodology takes advantage of the temporal nature of social events and as a side benefit, allows for scaling to real-world datasets. Specific challenges of the social event detection task are addressed: the engineering and selection of the features used to compare items to one another; a feature fusion strategy that incorporates relative importance of features; the construction of a single sparse affinity matrix; and clustering techniques which produce meaningful item groups whilst scaling to cluster very large numbers of items.The state-of-the-art approach presented here is evaluated using the ReSEED dataset with standardised evaluation measures. With automatically learned feature weights, we achieve an F1 score of 0.94, showing that a good compromise between precision and recall of clusters can be achieved. In a comparison with other state-of-the-art algorithms our approach is shown to give the best results

Social Event Detection at MediaEval: a three-year retrospect of tasks and results

Petkos G, Papadopoulos S, Mezaris V, et al. Social Event Detection at MediaEval: a three-year retrospect of tasks and results. In: Proc. ACM ICMR 2014 Workshop on Social Events in Web Multimedia (SEWM). 2014.This paper presents an overview of the Social Event Detection (SED) task that has been running as part of the MediaEval benchmarking activity for three consecutive years (2011 - 2013). The task has focused on various aspects of social event detection and retrieval and has attracted a significant number of participants. We discuss the evolution of the task and the datasets, we summarize the set of approaches ursued by participants and evaluate the overall collective progress that has been achieved

ADMRG @ MediaEval 2013 Social Event Detection

This paper elaborates the approach used by the Applied Data Mining Research Group (ADMRG) for the Social Event Detection (SED) Tasks of the 2013 MediaEval Benchmark. We extended the constrained clustering algorithm to apply to the first semi-supervised clustering task, and we compared several classifiers with Latent Dirichlet Allocation as feature selector in the second event classification task. The proposed approach focuses on scalability and efficient memory allocation when applied to a high dimensional data with large clusters. Results of the first task show the effectiveness of the proposed method. Results from task 2 indicate that attention on the imbalance categories distributions is needed