Abstract: A movement detector is included in television signal processing apparatus in order to improve the performance of the apparatus. The detector evaluates an absolute frame difference signal on a sample by sample basis and, after comparison with a threshold level signal in order to remove the effects of noise is fed to an isolated point removal circuit where samples deemed to indicate movement are compared with surrounding samples and if identified as isolated are ignored. Adaptive control is provided if the threshold, the isolated point removal circuit and a quantizer circuit for non-linearly altering the frame difference signal.

Abstract: A multiplexed analogue component (MAC) television signal is encrypted for transmission and reception by authorized recipients only by dividing the signal into blocks and reordering the blocks prior to transmission. The signal within each block remains in its original order. Preferably, the signal representing one line of video is split into blocks which are reordered within the line time to cause translation or rotation of analogue components. Alternatively a group of lines may be processed as a group to cause reordering of the analogue components between lines. The preferred arrangement does not split the blocks of analogue signals already present in the MAC signal. The receiver is arranged to receive information regarding the encryption technique with the television signal and to reorder the blocks constituting the received signal whereby to reconstruct the original signal.