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Television is now making huge changes. The most obvious change in recent years is the transition from analog to digital broadcasting. This transition means only changing the way television channels are distributed over terrestrial network. The old approach that worked for decades was using one analog transmitter to broadcast one TV channel using analog transmission technology. The new approach uses digital transmitters that broadcast a package of services (including many TV channels) called multiplex. The main reason for this change is efficient use of radio spectrum. This is a limited resource and therefore needs to be used efficiently. The other reason is implementation of new services and technologies that were not possible using analog broadcasting.
The first major difference is the picture resolution. The old analog TV is considered as a standard definition television (SDTV). This means that the picture has 480 lines (USA, Japan) or 625 lines (Europe and many other countries). Unfortunately only about 90% of those lines are visible on the screen. This low number of lines (and consequently low number of columns or pixels in each line) limits the resolution of the television picture. The latest trend is broadcasting high definition television (HDTV) picture which contains more lines and provides better picture with more details. HD television is only possible with digital broadcasting. This new technology together with more TV channels using the same frequency bandwidth is the biggest advantage of digital broadcasting.
HD means that the television picture contains 720 or more lines. The best HD picture contains 1080 lines and each line has 1920 pixels or points. This resolution is called Full HD. There are also other HD standards that have the number of lines between 720 and 1080. There are two variants of the HD picture: interlaced and progressive. Progressive mode means displaying HD images with all lines in each frame (static image that constitutes a moving picture). This way assures the best possible HD picture. The other alternative is interlaced mode which means alternatively displaying images with odd and even lines. This mode reduces needed bandwidth but also slightly reduces HD quality.
Plasma is a technology used to create HD screens. There are two competing technologies for HD screens: plasma and LCD. The old technology for analog SD television was the cathode ray tube (CRT) screen which was developed before the world war II. Both plasma and LCD work well and produce high quality HD images. In general, plasma is used for medium and large screens, while LCD is used for small and medium ones.
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