Abstract: A high definition image transmission system comprising a stage for the transmission of encoded data representative of images and, after transmission of these data at a specific field frequency and by a first channel having a limited passband, a stage for receiving the transmitted data. The transmission stage comprises an image encoding device having three processing channels in parallel for the purpose of transmission, at three separate transmission rates, of one or another of these three channels depending on the output signal of a decision circuit. It further comprises a device for decoding the encoded data, comprising three processing branches located in parallel and each receiving the sequence of the encoded data and a circuit for routing the outputs of the said branches according to the output signal of the decision circuit transmitted to the decoding device by a second channel called the digital assistance channel.

Abstract: In this system a transmission of certain high definition picture elements is provided such that at the receiving side it is possible to recover a picture of the normal definition without it being necessary to use additional circuits.

Abstract: Processing arrangement for enhancing signal contours of a signal, having a transition zone between low-amplitude and high-amplitude areas, including a device for multiplexing the samples of the input signal processed during the duration of the transition zone and non-processed samples located outside said zone. This multiplexing device is preceded by a first non-processed input sample transfer path (1) and, parallel thereto, a second path (2) for transferring processed input samples, the second transfer path including:(1) a circuit (10, 20, 30) for calculating the derivative and the sign of the derivative of the input signal;(2) a normalization circuit (50, 60, 70, 80, 90, 100);(3) a transformation circuit (1) for replacing each output value x of the first multiplier by a numerical equivalent of a function f(x) if x is not higher than 1/2, or by a numerical equivalent of a function 1-F(1-x) when x is higher than 1/2; and(4) a denormalization circuit (120, 130, 140, 150).

Abstract: A system for the transmission of high-definition television pictures in narrow-band channels, and a transmitter and a receiver appropriate to the system. The system includes a transmitting section (10) and a receiving section (20). To transmit the picture via a narrow-band channel (30), the picture produced by a camera (35) is subsampled by a circuit (40). One filter out of a plurality of anti-aliasing filters (F1, F2, . . . , Fn) is selected by means of a movement detector (48); the information of this detector is also transmitted to the receiving section (20) to select, in agreement therewith, one filter output of a plurality of filters (I1, I2, . . . , In) to be used for the oversampling operation.