1. A method to determine a descriptor for a signal representing a multimedia item input to a computer 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 directional filters in order to obtain a second set of coefficients representing the low-pass filtered signal, calculating a descriptor representing said multimedia element by calculating the difference between said first set of coefficients and said second set of coefficients, calculating associated power of said difference, and outputting the descriptors in response to the calculated associated power.