When
            you define a region of interest (ROI), playback performance can
            be improved by loading only the tiles required to display that ROI.
            You can choose to show or hide the areas of the loaded tiles that
            fall outside the ROI. 
         
         You can show or hide
            tiles in a Player view or the fullscreen Player.
         
         NoteYou can show or hide
               tiles in the fullscreen Player only if you entered it through a
               Player view. 
            
         To show or hide the area of the tiles
            that fall outside the region of interest:
         
         
            - In the Player view or fullscreen Player,
               middle-click or press the tilde key (~) to display the Gate UI and
               go through the south gate.
            
- In the Player options, select the Display
               tab.
            
- Under Interaction, select Mask Tiles. 
               NoteShow or hide tiles
                     is only available if you defined a region of interest in the image.