Figure 8. Octree of the optimized approach
For example, given the same threshold measurement, the original
octree approach constructs an octree as shown in Figure 7. The
motion vectors are all in the leaf nodes. Only the motion vectors
in the shaded nodes needs to be stored to reconstruct the
corresponding frame. In this scenario, the original approach needs
to store 15 * 8 motion vectors. In our proposed optimized
approach, the shape of the octree is exactly the same as the
original approach. But in the optimized approach, the motion
vectors are stored on some internal and leaf nodes. The unshaded
nodes inherit the motion vectors from its parents and it is not
necessary to store motion vectors themselves. In this case, the
optimized approach only needs to store 5 * 8 motion vectors to
restore the original frame in the decoder side. It significantly
reduced the storage space and transmission bandwidth.