1. A method of processing image data of a scene to provide depth information of the scene, the method comprising: providing, at each of a plurality of spatial resolution levels, a set of stereo images of the scene corresponding to a passive depth estimation technique and an active depth map corresponding to an active depth estimation technique; obtaining, at a higher spatial resolution level of the stereo images and respective active depth map, a global disparity map according to a cost function, the cost function being based on an estimated stereo disparity between corresponding pixels of the respective set of stereo images at the said higher spatial resolution level and on a determined consistency between the estimated stereo disparity and the respective active depth map of the scene at the said higher spatial resolution level; and wherein the disparity values of the global disparity map at the higher spatial resolution level are each estimated within a restricted disparity range determined based on disparity values of a global disparity map previously estimated for a corresponding set of stereo images and active depth map of the scene at a lower spatial resolution level.