A device 120 for processing three-dimensional [3D] image data 122 for display on a 3D display 160, the 3D display being arranged for adjacently emitting, in a viewing cone 180, a series of views 100 of the 3D image data, the series of views enabling autostereoscopic viewing of the 3D image data at multiple viewing positions 182, 184 in the viewing cone by a viewer perceiving two different ones of the series of views, and the device comprising an indicator generator 140 arranged for establishing a graphical shape in the 3D image data for, when being displayed on the 3D display, providing to the viewer a position indicator graphically representing a relative position of the two different ones of the series of views within the series of views.
