Patent ID: 8149916

Claim:
A method of coding video signals including coding groups of frames by motion compensated predictive coding relative to two other frames as reference frames, in accordance with an algorithm in which a region of a frame of the group is coded by a selected one of a plurality of possible methods which includes: a) forming the difference between that region and a portion of a first one of the reference frames, and a motion vector specifying the position of that portion of the first one of the reference frames relative to the region being coded; b) forming the difference between that region and a portion of the second of the reference frames, and a motion vector specifying the position of that portion of the second of the reference frames relative to the region being coded; and c) forming the difference between that region and a combination of a portion of a first one of the reference frames and a portion of the second of the reference frames, a first motion vector specifying the position of that portion of the first one of the reference frames relative to the region being coded and a second motion vector specifying the position of that portion of the second of the reference frames relative to the region being coded; enforcing that, for any region, that region is in one frame of the group coded using method (c) and the same region is, in other frames of the group, coded by one of said plurality of methods selected in dependence on a criterion as to the degree of similarity between the region being coded and, respectively, the said portion of the first reference frame, the said portion of the second reference frame and the said combination, wherein, in the frame(s) of the group other than one particular frame, each region is coded by one of said plurality of methods selected in dependence on said criterion; and in the particular frame of the group, each region is coded: (i) in the event that that region has not, in the frame(s) of the group other than the particular frame, been coded using method (c), using method (c) irrespective of said criterion; and (ii) in the event that that region has, in the frame(s) of the group other than the particular frame, been coded using method (c), using one of said plurality of methods selected in dependence on said criterion.