Y. Wang et J. Ostermann, EVALUATION OF MESH-BASED MOTION ESTIMATION IN H.263-LIKE CODERS, IEEE transactions on circuits and systems for video technology, 8(3), 1998, pp. 243-252
In this paper, we present two mesh-based motion estimation algorithms,
and evaluate their performance when incorporated in an H.263-like blo
ck-based video coder. Both algorithms compute nodal motions in a hiera
rchical manner. Within each hierarchy level, the first algorithm (HMMA
) minimizes the prediction error in the four elements surrounding each
node, where the prediction is accomplished by a bilinear mapping. The
optimal solution Is obtained by a full search within a range defined
by the topology of the mesh. The second algorithm (HBMA) minimizes the
error in a block surrounding each node, assuming the motion in the bl
ock is constant. In both cases, bilinear mapping is used for motion-co
mpensated prediction based on nodal displacements. The two algorithms
are compared with an exhaustive block-matching algorithm (EBMA) by eva
luating their performances in temporal prediction and in an H.263/TMN4
coder. For prediction only, the HMMA and HBMA algorithms yield visual
ly more satisfactory results, even though the PSNR's of predicted imag
es are on average lower. The coded images also have lower PSNR's at si
milar bit rates. The coding artifacts are different: while the block-b
ased method leads to more severe block distortions, the mesh-based met
hod experiences some warping artifacts. The HMMA algorithm outperforms
HBMA slightly for certain sequences at the expense of higher computat
ional complexity.