Teletext is a communication system wherein text and graphics are transmitted as digitized signals through air broadcasting or cable channel for display on television set. The television functions like a computer terminal to retrieve textual information and graphics from remote database. The information is stored in centralized databases, sequenced and indexed in the form of pages of text or graphics. The signal can be transmitted over one-way cable or by air. The digitalized text messages or pages of information are continuously broadcasted in cycle. A viewer can access to all these messages on a given channel in cycle or through control unit. Major applications of teletext are:
• Teletext uses the television for information display, which is almost universally present in homes or community centers. Thus it has the potential to become mass media for imparting education to students in general and deaf and hard-of-hearing viewers in particular.
• Teletext provides the educational content in a very concise and effective manner and thus makes learning appealing, interesting and less burdensome. Further, the facility of quick updation keeps it is viewers informed of the recent happenings. It can be a very good media for career counseling along with providing information about courses-in-demand, hot careers, job opportunities, etc.
• Teletext uses in the area of education, agriculture, weather forecasting, farm management, libraries, and industries etc. would provide effective management of services.
First form of Teletext was developed in the early 1970s by engineers at the British Broadcasting Company (BBC) and ITC (then known as IBA), the regulating body of commercial networks in the United Kingdom. General specification regarding teletext was published in United Kingdom in 1974. First teletext service was put into practice for general public use only in 1976.
Parallel to England’s teletext system, France proposed its own system - Antiope. This system introduced and used in 1977. Antiop was designed to transmit data over telephone lines. It failed to make use of many of the characteristics of the television signal. France’s another teletext service, Mintel overcame the limitations. During late seventies Canada developed a teletext service Telidon. It designed to produce high-quality graphics. This facility needed a complex decoder. The decoder was not commonly available to the consumer market at that time.
The teletext system transformed World System Teletext (WST) by 1984. More than 30 countries now use the enhanced version of WST worldwide, utilizing decoders installed in television receivers. The service is available in five levels, with each level showing an increasing array of enhancements and graphics sophistication. The higher levels require more complex decoding devices with progressively larger memories capable of storing great numbers of teletext pages; thus, receivers capable of decoding levels three, four and five may cost somewhat more than their less-sophisticated counterparts. (NCAM, 2002)