IMAGE DATA EDITING

A computer based image data processing system reads image data from a framestore and processes this data in response to user commands. In order to effect these commands the user is provided with a graphical user interface. In the interface a first region is displayed in which a number of clips representing an output sequence are represented by clip regions on a timeline, along with transitions between the clips which are represented by edit regions. The interface also displays a pointer that is arranged to move over the timeline, and a second region representing input controls. The controls relate to transition operations when the pointer is located over an edit region, and relate to other functions when the pointer is not located over an edit region.