1. A motion compensation deinterlacer for producing a progressive scan signal from an interlaced signal comprising: (a) a motion compensation unit for deriving missing lines in an interlaced field from at least one other field in the interlaced signal; (b) means for deriving a first confidence measure for the accuracy of the motion compensation unit using known lines of the field for which the missing lines are to be derived; (c) means for deriving a second confidence measure for the accuracy of the motion compensation unit using known lines of at least two other fields; (d) means for combining the first and second confidence measures; and (e) means for selecting outputs for display from at least the motion compensation unit and one other deinterlacing means in dependence on the combined confidence measure.