Some proposals use non-rectangular block representation models. Thus the motion estimation and compensation procedures must be adapted to them. For the non-feature points, the motion vectors are obtained by interpolating the feature points motion vectors. Warping prediction of triangular patches . The image is represented by a grid of triangular patches, allowing motion estimation by simply using the grid nodes motion vectors.
Compensation is done using warping prediction.
Warping prediction of sprites . A sprite trajectory, which is composed by the trajectories of several feature points on the sprite, is encoded. The sprite accretion process is composed of triangular tessellation of the visible part of the sprite in each frame, warping of each triangle using feature point correspondence and, accumulation of warped pixel information. A polygon defines the part of the contour of the macroblock which belongs to the VOP to be coded and excludes pixels outside of this area. Thus, pixels not belonging to the VOP are excluded from the motion estimation process.