Transmission techniques for picture Prestel

The teletext and videotex systems which are in service in the UK provide a mosaic type of graphics, permitting the display of simple pictures and diagrams. However several uses for an improved graphics facility have been identified which could benefit from still colour television pictures of normal definition and gradation. An experimental system has been developed to investigate the feasibility of such a picture option for future viewdata services. Since the available data rates are rather low for picture transmission, the application of image data compression techniques is imperative for acceptable picture update times at the receiver.