In the case of analogue TV transmissions, multiple images are scanned per second, each line-by-line. This results in a transferrable signal. The brightness correlates with the amplitude of the signal. The two additional pieces of colour information necessary can be added through the intensity of an integrated colour frequency and through the phase shifting of a colour subcarrier, which is signalled per line.
The most common standards are PAL and NTSC.
Existing physical networks are satellite television, cable networks and the terrestrial transmission.
In a limited scope, additional data can be transmitted in parallel (e.g. teletext).
In many households the analogue television remains the only method of receiving television. ITV concepts for broad target groups shall take this into account.
In the case of digital TV transmissions, multiple images are scanned and quantised two-dimensionally per second. This results in a matrix with discrete values. The matrix is mathematically transformed and effectively coded. At the end, a sequence of numbers exists which can be signalled by means of telecommunications.
In the majority of countries, the technology follows the international DVB (Digital Video Broadcasting) standard.
Digital television is also transmitted via satellite, cable and antenna.
Digital television facilitates enhanced quality and more efficient use of the bandwidths of the transfer medium. DVB also enables the transmission of any multimedia contents and applications. Furthermore, it is possible to control the synchronisation between television screen and application. The possibilities for interactive television are thus optimum.
Digital coding of the moving image also takes place with IPTV. This is comparable in principle with DVB. IPTV is primarily used in independent telecommunications networks. Technologies which are familiar from the internet are used in the transmission.
In terms of suitability for interactive television, it is at least comparable with DVB. However, standardisation, distribution and trialling are not yet complete.
Multicast TV via internet
The internet is not suitable for broadcasting from a technical perspective. The distribution of the internet does generate appeal with suppliers. Multicast would be an option for sending moving images to multiple registered internet users in a similar way to broadcasting. However, this technology is presently at the research stage.