Survey of Dirac: A Wavelet Based Video Codec for Multiparty Video Conferencing and Broadcasting - Intelligent Video Event Analysis and Understanding - page 225

Fig. 11 Correspondence of one block at lower level to 4 blocks at immediate higher level
For motion estimation, candidate lists of motion vectors are generated at the
lowest level. A candidate list consists of a number of vectors to be searched,
which are centered at predicted MV and follows a square pattern at each level.
The predicted MV can be zero MV, spatially predicted MV or guide MV.
Spatially predicted MV may be zero MV, motion vector of previous horizontal
block, motion vector of previous vertical block, the median of motion vectors of
blocks 1, 2 and 3 for middle blocks and the mean of motion vectors of blocks 1
and 2 for last column blocks as shown in the Figure 10, depending upon the
location of current block where motion estimation is performed. Guide MV is the
best motion vector of a block at the lower level in the hierarchy and it is not
available for lowest level.
Fig. 12 Spatially Predicted Motion Vector of Dirac
Motion estimation is started at lowest level in the hierarchy. For lowest level,
two candidate lists are generated, one is centered at zero MV and the other is
centered at spatially predicted MV. For all other levels, three candidate lists are
generated, two are same as above and the third list is centered at guide motion
vector, which is the best motion vector of the corresponding block in the