2016
Authors
Pereira, EM; Cardoso, JS; Morla, R;
Publication
JOURNAL OF VISUAL COMMUNICATION AND IMAGE REPRESENTATION
Abstract
Motion is a fundamental cue for scene analysis and human activity understanding in videos. It can be encoded in trajectories for tracking objects and for action recognition, or in form of flow to address behavior analysis in crowded scenes. Each approach can only be applied on limited scenarios. We propose a motion-based system that represents the spatial and temporal features of the flow in terms of I ong-range trajectories. The novelty resides on the system formulation, its generic approach to handle scene variability and motion variations, motion integration from local and global representations, and the resulting long-range trajectories that overcome trajectory-based approach problems. We report the results and conclusions that state its pertinence on different scenarios, comparing and correlating the extracted trajectories of individual pedestrians, manually annotated. We also propose an evaluation framework and stress the diverse system characteristics that can be used for human activity tasks, namely on motion segmentation.
2017
Authors
Pereira, EM; Ciobanu, L; Cardoso, JS;
Publication
NEURAL COMPUTING & APPLICATIONS
Abstract
The increasing demand for human activity analysis in surveillance scenarios has been triggered by the emergence of new features and concepts to help in identifying activities of interest. However, the characterisation of individual and group behaviours is a topic not so well studied in the video surveillance community due to not only its intrinsic difficulty and large variety of topics involved, but also because of the lack of valid semantic concepts that relate human activity to social context. In this paper, we address the topic of social semantic meaning in a well-defined surveillance scenario, namely shopping mall, and propose new definitions of individual and group behaviour that consider environment context, a relational descriptor that emphasises position and attention-based characteristics, and a new classification approach based on mini-batches. We also present a wide evaluation process that analyses the sociological meaning of the individual features and outlines the performance impact of automatic features extraction processes into our classification framework. We verify the discriminative value of the selected features, state the descriptor performance and robustness over different stress conditions, confirm the advantage of the proposed mini-batch classification approach which obtains promising results, and outline future research lines to improve our novel social behavioural analysis framework.
2015
Authors
Costa, J; Cardoso, JS;
Publication
ICPRAM 2015 - Proceedings of the International Conference on Pattern Recognition Applications and Methods, Volume 1, Lisbon, Portugal, 10-12 January, 2015.
Abstract
Ordinal data classification (ODC) has a wide range of applications in areas where human evaluation plays an important role, ranging from psychology and medicine to information retrieval. In ODC the output variable has a natural order; however, there is not a precise notion of the distance between classes. The Data Replication Method was proposed as tool for solving the ODC problem using a single binary classifier. Due to its characteristics, the Data Replication Method is straightforwardly mapped into methods that optimize the decision function globally. However, the mapping process is not applicable when the methods construct the decision function locally and iteratively, like decision trees and ADABOOST (with decision stumps). In this paper we adapt the Data Replication Method for ADABOOST, by softening the constraints resulting from the data replication process. Experimental comparison with state-of-the-art ADABOOST variants in synthetic and real data show the advantages of our proposal.
2015
Authors
Xiao, XH; Peng, MF; Cardoso, JS; Tang, RJ; Zhou, YL;
Publication
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING
Abstract
Micro-solder joint (MSJ) lifetime prediction methodology and failure analysis (FA) are to assess reliability by fatigue model with a series of theoretical calculations, numerical simulation and experimental method. Due to shortened time of solder joints on high-temperature, high-frequency sampling error that is not allowed in productions may exist in various models, including round-off error. Combining intermetallic compound (IMC) growth theory and the FA technology for the magnetic head in actual production, this thesis puts forward a new growth model to predict life expectancy for solder joint of the magnetic head. And the impact of IMC, generating from interface reaction between slider (magnetic head, usually be called slider) and bonding pad, on mechanical performance during aging process is analyzed in it. By further researching on FA of solder ball bonding, thesis chooses AuSn4 growth model that affects least to solder joint mechanical property to indicate that the IMC methodology is suitable to forecast the solder lifetime. And the diffusion constant under work condition 60 A degrees C is 0.015354; the solder lifetime t is 14.46 years .
2013
Authors
Sousa, R; Cardoso, JS;
Publication
AI COMMUNICATIONS
Abstract
Classification is one of the most important tasks of machine learning. Although the most well studied model is the two-class problem, in many scenarios there is the opportunity to label critical items for manual revision, instead of trying to automatically classify every item. In this paper we tailor a paradigm initially proposed for the classification of ordinal data to address the classification problem with reject option. The technique reduces the problem of classifying with reject option to the standard two-class problem. The introduced method is then mapped into support vector machines and neural networks. Finally, the framework is extended to multiclass ordinal data with reject option. An experimental study with synthetic and real datasets verifies the usefulness of the proposed approach.
2016
Authors
Sequeira, AF; Thavalengal, S; Ferryman, J; Corcoran, P; Cardoso, JS;
Publication
2016 39TH INTERNATIONAL CONFERENCE ON TELECOMMUNICATIONS AND SIGNAL PROCESSING (TSP)
Abstract
Iris liveness detection methods have been developed to overcome the vulnerability of iris biometric systems to spoofing attacks. In the literature, it is typically assumed that a known attack modality will be perpetrated. Then liveness models are designed using labelled samples from both real/live and fake/spoof distributions, the latter derived from the assumed attack modality. In this work it is argued that a comprehensive modelling of the spoof samples is not possible in a real-world scenario where the attack modality cannot be known with a high degree of certainty. In fact making this assumption will render the liveness detection system more vulnerable to attacks that were not included in the original training. To provide a more realistic evaluation, this work proposes: a) testing the binary models with unknown spoof samples that were not present in the training step; b) the use of a single-class classification designing the classifier by modelling only the distribution of live samples. The results obtained support the assertion that many evaluation methods from the literature are misleading and may lead to optimistic estimates of the robustness of liveness detection in practical use cases.
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