An EM algorithm to learn sequances in the wavelet domain.

D. H. MILONE; L. E. DI PERSIA

MICAI 2007: Advances in Artificial Intelligence

Springer

Lugar: Berlin; Año: 2007; p. 518 - 528

The wavelet transform has been used for feature extraction in many applications of pattern recognition. However, in general the learning algorithms are not designed taking into account the properties of the features obtained with discrete wavelet transform. In this work we propose a Markovian model to classify sequences of frames in the wavelet domain. The architecture is a composite of an external hidden Markov model in which the observation probabilities are provided by a set of hidden Markov trees. Training algorithms are developed for the composite model using the expectation-maximization framework. We also evaluate a novel delay-invariant representation to improve wavelet featureextraction for classification tasks. The proposed methods can beeasily extended to model sequences of images. Here we present phoneme recognition experiments with TIMIT speech corpus. The robustness of the proposed architecture and learning method was tested by reducing the amount of training data to a few patterns. Recognition rates were better than those of hidden Markov models with observation densities based in Gaussian mixtures.