1. A method of analyzing an input video sequence to associate pixels of synthesized images of an output video sequence with respective directions of regularity belonging to a predefined set of directions, the method comprising: determining, from the predefined set of directions, a first subset of candidate directions for a region of a first image of the output video sequence; determining, from the predefined set of directions, a second subset of candidate directions for a corresponding region of a second synthesized image of the output video sequence following the first image, based on images of the input video sequence and the first subset of candidate directions; wherein determining the second subset of candidate directions includes, evaluating a first margin for a first direction of the first subset, the first margin equal to a contribution of the first direction to a reduction of a cost function associated with the first subset, evaluating a second margin for a second direction of the predefined set of directions, the second margin equal to a decrement of the cost function associated with the first subset resulting from addition of the second direction to the first subset, and substituting the second direction for the first direction responsive to the second margin exceeding the first margin; and detecting the respective directions of regularity for pixels of said region of the second synthesized image from the second subset of candidate directions.