During a video encoding or decoding process, a predicted prediction block is generated for a CU. The CU may have two or more prediction units (PUs). A computing device selects a neighbor region size. After the computing device selects the neighbor region size, samples in a transition zone of the prediction block are identified. Samples associated with a first PU are in the transition zone if neighbor regions that contain the samples also contain samples associated with a second PU. Samples associated with the second PU may be in the transition zone if neighbor regions that contain the samples also contain samples associated with the first PU. The neighbor regions have the selected neighbor region size. A smoothing operation is then performed on the samples in the transition zone.