Television band compression by contour interpolation

Abstract
Band saving in television transmissions can be achieved by utilizing redundancies in single lines, between lines, between fields and between frames. The method of contour interpolation exploits the last two. It is based on the facts that (a) field and frame frequencies in conventional television transmission had to be chosen with a view to reducing flicker rather than for conveying more information, (b) the eye fixes mainly on contours which are usually the edges of objects, (c) these contours are usually smooth enough to allow interpolation over two line spacings, and (d) changes from one picture to the next come about mostly by the horizontal motion of objects which are sufficiently uniform to allow interpolation over at least two frame intervals. There is almost no loss in information or picture quality if the interlaced frame is suppressed in the transmission and reconstructed in the receiver by interpolation between the lines of the transmitted field, and there is not much loss if only one field in four is transmitted. In the method of contour interpolation the reconstructed edges are as sharp as the originals and appear in their correct positions, i.e. in the positions which they would occupy if the edges were straight in small sections, and if their motion were uniform for short times. The waveband gain can be estimated as 4 : 1 without appreciable deterioration in picture quality, and 8 : 1 if some deterioration is allowed in the case of rapid and vertical motions. In combination with other methods which utilize redundancies in single lines and which by themselves achieve a gain of 3 : 1, total compression ratios of 12 : 1 to 24 : 1 appear feasible.The principle was realized and tested in a photo-mechanical model working at low speeds. Electronic realizations are proposed and discussed.

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