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.