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An important issue in data analysis and pattern classification is the detection of anomalous observations and its influence on the classifier's performance. In this paper, we introduce a novel methodology to systematically compare the performance of neural network (NN) methods applied to novelty detection problems. Initially, we describe the most common NN-based novelty detection techniques. Then we generalize to the supervised case, a recently proposed unsupervised novelty detection method for computing reliable decision thresholds. We illustrate how to use the proposed methodology to evaluate the performances of supervised and unsupervised NN-based novelty detectors on a real-world benchmarking data set, assessing their sensitivity to training parameters, such as data scaling, number of neurons, training epochs and size of the training set. [ABSTRACT FROM AUTHOR]

In this paper potential active contours are presented as a new method of image segmentation. The concept of potential contour is a result of the relationship between active contour techniques and the methods of classifiers' construction. The proposed method can be extended by the adaptation mechanism that allows changing the available class of the shapes dynamically. An original contribution is also the method of evaluation of segmentation results and methodology used for the parameters selection. The described method is illustrated by two examples. [ABSTRACT FROM AUTHOR]

This paper describes in full detail a model of a hierarchical classifier (HC). The original classification problem is broken down into several subproblems and a weak classifier is built for each of them. Subproblems consist of examples from a subset of the whole set of output classes. It is essential for this classification framework that the generated subproblems would overlap, i.e. some individual classes could belong to more than one subproblem. This approach allows to reduce the overall risk. Individual classifiers built for the subproblems are weak, i.e. their accuracy is only a little better than the accuracy of a random classifier. The notion of weakness for a multiclass model is extended in this paper. It is more intuitive than approaches proposed so far. In the HC model described, after a single node is trained, its problem is split into several subproblems using a clustering algorithm. It is responsible for selecting classes similarly classified. The main scope of this paper is focused on finding the most appropriate clustering method. Some algorithms are defined and compared. Finally, we compare a whole HC with other machine learning approaches. [ABSTRACT FROM AUTHOR]

Classifier combination has repeatedly been shown to provide significant improvements in performance for a wide range of classification tasks. In this paper, we focus on the problem of combining probability distributions generated by different classifiers. Specifically, we present a set of new combination rules that generalize the most commonly used combination functions, such as the mean, product, min, and maxoperations. These new rules have continuous and differentiable forms, and can thus not only be used for combination of independently trained classifiers, but also as objective functions in a joint classifier training scheme. We evaluate both of these schemes by applying them to the combination of phone classifiers in a speech recognition system. We find a significant performance improvement over previously used combination schemes when jointly training and combining multiple systems using a generalization of the product rule. [ABSTRACT FROM AUTHOR]

Combination (ensembles) of classifiers is now a well established research line. It has been observed that the predictive accuracy of a combination of independent classifiers excels that of the single best classifier. While ensembles of classifiers have been mostly employed to achieve higher recognition accuracy, this paper focuses on the use of combinations of individual classifiers for handling several problems from the practice in the machine learning, pattern recognition and data mining domains. In particular, the study presented concentrates on managing the imbalanced training sample problem, scaling up some preprocessing algorithms and filtering the training set. Here, all these situations are examined mainly in connection with the nearest neighbour classifier. Experimental results show the potential of multiple classifier systems when applied to those situations. [ABSTRACT FROM AUTHOR]