A method of displaying an image on a display device having a plurality of display panels , the display panels together forming a single display screen for displaying at least one complete image, each display panel having a display input connected to a display controller of a plurality of display controllers for receiving display data of a portion of the complete image, wherein each display controller of the plurality of display controllers provides display data for one or more display panels , wherein the complete image is formed of a plurality of tiles of display data and each display panel displays the display data of the tiles forming the portion of the complete image for display on that display panel , the complete image including one or more bounded regions of display data, wherein each bounded region is displayed and may be moved as a whole to at least partly change position laterally from one display panel to another within the complete image or to have a new position within a stacking order of a plurality of bounded regions, wherein the stacking order provides an order whereby only one or more topmost bounded region(s) in the stacking order would be displayed in the complete image, the method comprising, at a display controller : receiving at least the display data destined for a display panel connected to the display controller ; receiving position information relating to a change in lateral position and/or stacking order position of one or more bounded regions that are to be displayed at least partly on a display panel connected to the display controller ; determining whether the display controller already has knowledge of the tiles of display data in the bounded region to be displayed on the display panel for which the position information was received, wherein the knowledge of a tile comprises either the display data for that tile, or an address in memory where the display data for that tile may be accessed; if the display controller determines that it does not have knowledge of one or more of the tiles in the bounded region, obtaining knowledge of the one or more tiles from another display controller that has such knowledge; processing the display data for the portion of the complete image utilising the knowledge of the one or more tiles obtained from another display controller ; and outputting the processed display data for the portion of the complete image to the corresponding display panel . receiving at least the display data destined for a display panel connected to the display controller ; receiving position information relating to a change in lateral position and/or stacking order position of one or more bounded regions that are to be displayed at least partly on a display panel connected to the display controller ; determining whether the display controller already has knowledge of the tiles of display data in the bounded region to be displayed on the display panel for which the position information was received, wherein the knowledge of a tile comprises either the display data for that tile, or an address in memory where the display data for that tile may be accessed; if the display controller determines that it does not have knowledge of one or more of the tiles in the bounded region, obtaining knowledge of the one or more tiles from another display controller that has such knowledge; processing the display data for the portion of the complete image utilising the knowledge of the one or more tiles obtained from another display controller ; and outputting the processed display data for the portion of the complete image to the corresponding display panel . <EOS>