1. A method of processing successive images of a video signal to generate a representative color value indicative of a representative color of an image sub-area, said method comprising the steps of: (i) detecting a color property of said image sub-area in a current image; (ii) generating a filtered color property in respect of said current image by combining a color property for said current image with a filtered color property derived in respect of a corresponding sub-area of a previous image; and (iii) deriving said representative color value in dependence on a difference between said color property of said sub-area of said current image and said filtered color property.