In this paper, a novel representation for facial expressions in
two-dimensional image sequences is presented. We apply a variation of
two-dimensional heteroscedastic linear discriminant analysis (2DHLDA)
algorithm, as an efficient dimensionality reduction technique, to Gabor
representation of the input sequence. 2DHLDA is an extension of the
two-dimensional linear discriminant analysis (2DLDA) approach and removes the
equal within-class covariance. By applying 2DHLDA in two directions, we
eliminate the correlations between both image columns and image rows.