A plurality of input video signals (including background) are combined in accordance with priority. Each video signal comprises data samples corresponding to respective discrete locations on a viewing plane. The signals are preferably from an ADO transformation system wherein such data samples correspond to elements of an image lying in an image plane displaced from the viewing plane. Input key signals correspnding to respective locations are associated with respective input signals. Priority is shown determined from respective sets of plane defining signals as a sequence of depth signals corresponding to the depth coordinates of the respective image plane at the respective locations. The depth signals are used to produce respective weighting signals. The weighting signals and respective input key signals are used to produce in respect to each input video signal a set of processed key signals corresponding to respective coordinate locations on the viewing plane in the respective sequence, each set of processed key signals indicating the weighted portion of the respective data samples to be included in a combined video signal at each respective coordinate location. Corresponding data samples are cut by respective processed key signals to produce weighted data samples in respect to each input video signal in the respective sequence. The weighted data samples of the plurality of input video signals for each respective coordinate location on the viewing plane are combined in the respective sequence to produce a combined output video signal.