1. An image processor (PLY) for processing an assembly of data (DDS) that defines an elementary image and a graphics object, the assembly of data comprising composition data (CS) that defines a given appearance of the graphics object in an output image (OI) wherein the graphics object overlays a portion of the elementary image, the image processor comprising: an occlusion analyzer (OCA) for establishing an occlusion indication (OCS) on the basis of the composition data (CS), the occlusion indication specifying an area in the elementary image that the graphics object will occlude in the output image (OI), but that may be de-occluded in a stereoscopic rendering of the output image; an occlusion data generator (ODG) for composing an occlusion image on the basis of the occlusion indication (OCS) and the elementary image, the occlusion image representing a portion of the elementary image that corresponds with the area specified by the occlusion indication.