1. A method of generating a disparity map for an image sequence displayable on a screen defining a screen plane, wherein the image sequence includes a stereoscopically viewable first object perceivable by a viewer on an image plane different to the screen plane, the stereoscopically viewable object comprising a first image frame viewable by a viewer's eye and a second image frame viewable by the viewer's other eye, the method comprising: performing a first edge pixel detection process on the first image frame to identify edges within the first image frame; identifying a feature pixel of the first image from the detected edges; generating a block of pixels including the feature pixel, performing block matching on a search region of the second image using the block of pixels from the first image frame, wherein the block of pixels generated from the first frame is correlated against the search region; and generating a disparity map by identifying a relative displacement of the feature pixel of the first image frame from a corresponding feature pixel in the second image frame, wherein prior to performing the first edge pixel detection process, a sub-harmonic summation process is applied to an auto-correlated version of at least one of the first image frame and the second image frame to determine a magnitude of a fundamental frequency of a repeating pattern present in the at least one frame, and the first edge pixel detection process and the generating the disparity map are performed in dependence on the magnitude of the fundamental frequency of the at least one image frame.