IF You want to sell off your car, how about advertising on television? If you are thinking about the expenses, don't worry - it will be cheap enough, thanks to the efforts of researchers from Viewcall, a company set to storm Britain's information superhighway. The firm has developed a new technology that makes it possible to transmit high quality still pictures, text and sound over conventional copper telephone lines to standard television sets in an interactive manner.

The technology will enable a subscriber to the Viewcall multimedia service to view what can be described as a cross between classified advertisements in local newspapers and cinema trailers for neighbourhood businesses at the flick of a button on the TV remote. Coloured photographs of the various second-hand cars for sale and other relevant details regarding the vehicles would be accessed as on screen display. More key depressions may enable you to express interest in particular models and also arrange for test drives.

Viewcall differs from other multimedia services in many respects, say company officials. First, it will be cheap - about E2 a week for residential customers. Second, it will offer only home shopping or advertising. Third, it will be local in style and content.

John Bentley and David Boyce, executive chairperson and chief operating officer of Viewcall respectively, argue that the conventional approach to the information superhighway - based on expensive and technically difficult services such as voice on demand - is fundamentally flawed. Its operating costs are high, they say, pointing to studies which indicate the cost of providing interactive shopping services over cable at $5,000. The Viewcall system works out at just $250 a home.

The Viewcalt system comprises a number of servers or database computers. Information is transmitted down conventional telephone lines to a set top box designed by Online Media - division of Acorn Computer,. Viewcall's chief selling point is the quality of graphics that it can transmit - images of almost photographic quality and clarity. This has been made possible by a mathematical method called fractal compression for squeezing down the number of binary digits needed to transmit an image.

Compared to the ordinary television advertising, the Viewcall system works out to be cheap. Viewcall has already demonstrated the latest version of its system at London's Cafe Royal and intends inviting content providers to sign up for trials.