1. A method to determine a descriptor for a signal representing a multimedia item comprising the step of applying to said signal a first bank of directional filters in order to obtain a first set of coefficients, wherein it comprises the steps of applying to said signal a second bank of filters in order to obtain a second set of coefficients representing the low-pass filtered signal, calculating a descriptor representing said multimedia element by making the difference between said first set of coefficients and said second set of coefficients and calculating associated power of said difference.