A method is described of compositing a plurality of graphical objects to create an image comprising a plurality of parts, where the parts may be a run of pixels along a scanline or a region of the image. For each part of the image to be composited, the method identifies a set of the graphical objects that contribute to the part, and determines one or more required bit depths for compositing the set. The set is composited within the part at the one or more required bit depths. Thus selected parts of the image may be generated using a higher compositing bit depth.
