1. A method of determining a relightable texture for use in rendering an image from a rendering viewpoint under arbitrary lighting conditions, wherein at least one view of a scene from a respective at least one camera viewpoint represents the image, the method comprising: separating an initial texture for the image into a lighting estimate and a colour estimate, said initial texture being derived from the at least one view of the scene from the at least one camera viewpoint; generating a shadow-detail estimate by filtering the lighting estimate to attenuate low frequency components thereof, wherein the shadow-detail estimate indicates one or more shadow regions of the relightable texture which are to remain in shadow when the image is rendered; and determining the relightable texture for the image using the lighting estimate, the colour estimate and the shadow-detail estimate.