A face classification system comprises means (3) for extracting a face from a two dimensional representation of a three dimensional scene. The input signal is applied to a homomorphic filter (2) to eliminate the effects of lighting changes in the scene. A rotation, scaling, and translation invariant representation of the face is produced (7) by means of recursive second order sub-division of moments to produce a feature vector representative of the face. The positions of the eyes and mouth are located (6) to enable two sub-divisions, one on a line joining the eyes and the other on a line perpendicular to the first line and passing through the nose. The recursive second order sub-division of moments is constrained to act first to sub-divide on these lines which reduces the effect of noise on the feature vector. The feature vector is then applied to a classifier 8, which may take the form of a multilayer perception, where it is compared with one or more previously stored faces to determine whether there is a match. Such a system may be used in security systems, for example for allowing access to secure areas or for computer workstations. <IMAGE>
Classifying faces