An image processor processes an assembly of data that defines an elementary image and a graphics object. The assembly of data includes composition data that defines a given appearance of the graphics object in an output image, where the graphics object overlays a portion of the elementary image. The image processor includes an occlusion analyzer for establishing an occlusion indication based on the composition data. The occlusion indication specifies an area in the elementary image that the graphics object will occlude in the output image, but which may be de-occluded in a stereoscopic rendering of the output image. An occlusion data generator composes an occlusion image based on the occlusion indication and the elementary image. The occlusion image represents a portion of the elementary image that corresponds with the area specified by the occlusion indication.