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Which Color TV norms and transmission standards are there?
Autor: Johannes Post
04/19/2005, 01:24 CET
TVs and LCD TVs often integrate one or two multiple norm TV tuners for antenna/ cable connection.
There are several transmission standards for encoding video information. PAL (Phase Alternating Line) is very common in Central Europe. SECAM (Séquentiel Couleur à Mémoire) in France and Eastern Europe, and NTSC (National Television System Committee) in the USA and Japan.
PAL has 576 visible lines. It transmits 50 interlaced pictures per seconds. Interlaced pictures are also called fields in technical lingo. First all uneven numbered lines and then all even lines of a frame (frame = picture) are transmitted by turns which results in 25 pictures per second. This process is called Interlacing (line spacing).
Right picture: field with uneven numbered lines (odd field/ top field)
Left picture: even numbered lines (even field, bottom field)
Both pictures together as an animation simulating the Interlacing.
PAL includes a phase shift between the chrominance color signal of the separate lines by 180 degrees which compensates transmission errors by using the average values of two lines as the respective color tones.
NTSC uses 480 visible lines. It transmits 60 interlaced pictures per seconds. NTSC suffers from the major disadvantage of phase shifts occurring during the transmission which leads to wrong colors. For instance, skin color tones often easily drift over to a lurid pink color tone.
In contrast to PAL and NTSC, SECAM doesn't use one carrier frequency but two. While PCAL and NTSC make use of quadrature modulation, a more stable carrier frequency is deployed in SECAM whereat respectively only one of the two color components is transmitted at once by turns. In doing so, SECAM - just as PAL - results in more stable color tones and avoids the problems that NTSC is struggling with in regard to color stability.
DVB is short for Digital Video Broadcasting - in other words: digital TV. DVB transmits video information digitally in MPEG2 format. There are several DVB standards:
* DVB-C (Digital Video Broadcasting Cable), standard for digital cable transmission.
* DVB-S (Digital Video Broadcasting Satellite), standard for digital satellite transmission.
* DVB-T (Digital Video Broadcasting Terrestrial), standard for digital terrestrial transmission.
Different modulation processes are being deployed for the various transmission paths of digital channels. Cables uses QAM, satellite uses QPSK and terrestrial antenna uses COFDM. Each of the DVB standards requires the appropriate receiver, since there is no DVB receiver yet which supports all of the three aforementioned modulation processes unifying them in all in a single device.
Only a handful of LCD TVs are equipped with a DVB receiver, but here again, never is there more than one of the three supported.
HDTV (High Definition Television) is a new standard offering multiple high resolution TV formats, for instance HDTV 720p (1280 x 720 Pixel progressive) or HDTV 1080i (1920 x 1080 Pixel interlaced).
At the present time, there is no TV featuring an integrated HDTV Tuner yet. So one will have to obtain an external satellite receiver separately.
Compared to other countries, Germany unfortunately is somewhat behind on the road to HDTV. HDTV is already pretty wide spread in Japan or the USA while Germany hasn't even finished the test stage with occasional test broadcasts of shows in HDTV.