Introduction to the special issue on digital television

Up until recently, all through the history of mankind, the hearth has been the source of heat and of prepared food and as such the centre around which a house was built and the family gathered. In the last three decades television has changed society to an extent that this is no longer true. In the civilized world the hearth has been replaced by a distributed source ofheat, the position ofthe family is no longer unique and heat and prepared food no longer determine the house centre. The television set is more often than not in the dominant position now, it is the window to the outside world and television watching consumes a substantial amount ofthe time one is free to spend. The invention of the art of printing was highly instrumental in the change of society, around half a millennium ago, when the large-scale distribution of written information undermined the authority of traditional institutions and people's attitudes to them. The worldwide introduetion oftelevision and its continuous expansion generated a similar change, with larger impact because of the easier access of the intellectual content due to the visual support. The weaker dependence on the written language contributed to the interconnection of large sections of mankind, up to then unknown to each other, and often therefore made enemies more easily. Whether all of the effects of television are to be judged as positive and desirable, could be subject to discussion and largely represents a personal attitude, but the facts are undeniable. Apart from the social impact the facility oftelevision is important for industrial and economic reasons. The hardware content demands an elaborated infrastructure for signal delivery and both at the transmitter and receiver ends technology is available at a level of complexity of which the most daring forecaster could not have dreamed. At the receiver end this is available for a price allowing it to be within everybody's reach. For a long time the television transmission chain has been considered as a technically underused facility which, to begin with for economic reasons, is in need of further applications. Like all technical products television shows a continuous improvement in lifetime and performance, generally taking advantage of