motion estimation and compensation for very low bitrate video coding

3.2 Distributed Version of the Local Motion Estimation 91
gated" states because the previous iteration for these neighbors has not
completed yet. One has to wait for \Propagated" blocks to fall into the
\Done" or \Split" state ( gure 3.7). In the latter case, the transition
condition is determined by the appropriate subblock.
Similarly to what has just been presented, the non-linear ltering of a
block (and the decision algorithm) can start as soon as its 8 neighbors are
either in the \Propagated" state, either in the \Done" or \Split" state.
In every case, it is the vector value resulting from the \Propagated" state
that is to be used. Once again, some neighbor blocks can have a larger
size. They can only be neighbors via the diagonal because horizontal
and vertical blocks had to be over the \Propagated" state during the
previous step. One has to wait until such larger blocks fall into the
\Done" or \Split" state.
So as to somehow complete this informal description of the transition
conditions, some additional properties should be described. Figure 3.8
presents an impossible situation where a block has as neighbors bigger
blocks in \Known" or \Unknown" state. This case is impossible because
the block undergoing treatment results from a bigger block that has
been split after the motion certitude treatment and the ltering (what
implies that all its neighbors were at least in the \Propagated" state).
P
P
K
Figure 3.8: Impossible situation
But there can be more than one di erence of size between two neighbor
blocks. If it is the case, the biggest blocks must absolutely be in the
\Done" state as illustrated on gure 3.9.
To achieve the practical implementation, Vermaut has developed all the
necessary structures to manage the block data and to keep in memory
the block position in the image, its size, its present state and related
information, and a list of neighbors. E cient ways of performing the
wakening of a block have also been erected.