A method of video motion estimation is described for determining the dominant
motion
in a video image. The dominant motion is defined by a parametric transform, for
example a similarity transform. In the preferred embodiment, selected pairs of
blocks in one frame are traced by a block matching algorithm into a subsequent
frame, and their change in position determined. From that information, an individual
parameter estimate is determined. The process is repeated for many pairs of blocks,
to create a large number of parameter estimates. These estimates are then sorted
into an ordered list, the list is preferably differentiated, and the best global
value for the parameter is determined from the differentiated list. One approach
is to take the minimum value of the differentiated list, selected from the longest
run of values which fall below a threshold value. Alternatively, the ordered list
may be examined for flat areas, without explicit differentiation. The technique
is particularly suited to low complexity, low bit rate multimedia applications,
where reasonable fidelity is required without the computational overhead of full
motion compensation.