1. A method for processing an image signal, comprising the steps of: (a) subdividing the image signal into a plurality of distinct regions, including an upper region and a lower region, and at least one transition zone between the upper and lower regions; (b) constructing a plurality of separate curves, one for each region; (c) smoothing each curve independently of the other curves; and (d) reconstructing the image signal from the smoothed curves such that the reconstructed image signal has no segment in any transition zone.