1. A method performed by an image display system, the method comprising: accessing an image frame; and generating first and second sub-frames from the image frame for simultaneous display by first and second display devices respectively, in at least partially overlapping positions on a display surface so that a simulated image formed from the first and the second sub-frames approximates, subject to at least one smoothing constraint, a target image formed from the image frame and at least one property of each of the first and the second display devices.