SECAM
SECAM (Sequentiel Couleur avec Mémoire, French for "sequential color with memory") is an analog color television system first used in France.
Technical details
SECAM uses frequency modulation to encode chrominance information. It is so named because it uses memory to store lines of color information, in order to eliminate the color artifacts found on systems using the NTSC standard.
It was developed for the same purpose as PAL, but employs a different mechanism. R-Y and B-Y information is transmitted in alternate lines, and a video line store (a 64 µs delay line) is used to combine the signals. This means that the vertical colour resolution is halved relative to NTSC. It is however not halved compared to PAL, which also combines color information from adjacent lines at the decoding stage, in order to compensate for color subcarrier phase errors occurring during the transmission. This is normally done using a delay line borrowed from SECAM (the result is called PAL DL or PAL Delay-Line, sometimes interpreted as DeLuxe), but can be accomplished "visually" in cheap TV sets (PAL standard). Phase errors do not cause loss of color saturation in SECAM, although they do in PAL.
SECAM is also free of the dot crawl problem commonly encountered with the other analog standards and first widely noticed with the Laserdiscs. Dot crawl can be removed from 'PAL standard'- and NTSC-encoded signals using a comb filter.
The idea of reducing the vertical color resolution comes from Henri de France, the inventor, who first observed that color information is approximately identical for two successive lines. DVD and other digital television formats have perpetuated the implementation of this idea. Hence, paradoxically, VHS NTSC videos can have a greater vertical color resolution than DVD.
Note that all analog color standards reduce the horizontal color resolution, by transmitting the chrominance with a limited bandwidth.
History
Work on SECAM began in 1956. The technology was ready by the end of the fifties, but this was too soon for a wide introduction. Notably, SECAM did not work with the 819-line television standard then used by the then sole French TV network. France had to start the conversion by switching over to a 625-line television standard, which happened at the beginning of the sixties with the introduction of a second network.
SECAM was inaugurated in France on October 1st 1967, on la seconde chaîne (the second network), currently called France 2. At that time a color television set cost 5000 Francs. Color TV was not very popular initially; only about 1500 people watched the inaugural program. A year later, only 200,000 sets had been sold of an expected million.
SECAM was later adopted by former French and Belgian colonies, Eastern European countries, the former Soviet Union and Middle Eastern countries. However, with the fall of communism, and following a period when multi-standard TV sets became a commodity, a lot of Eastern European countries decided to switch to PAL.
Why SECAM in France?
Many have argued that the primary motivation for the development of SECAM in France was to protect French television equipment manufacturers. However, incompatibility had started with the earlier decision to uniquely adopt positive video modulation for French broadcast signals. Also, SECAM development predates PAL; and because of frame rate differences (50 versus 60 Hz) and the requirement for compatibility with monochrome TV receivers, it was not possible for Europeans to adopt NTSC. SECAM and PAL addressed the chroma phase problem with NTSC which required the tint control on U.S. sets.
Nonetheless, SECAM was partly developed for reasons of national pride. Henri de France's personal charisma and ambition may have been a contributing factor.
Unlike some other manufacturers, the company where SECAM was invented, Thomson, still sells TV sets worldwide under different brands; this may be due in part to the legacy of SECAM. Thomson bought the company which developed PAL, Telefunken, and today even co-owns the RCA brand — RCA being the creator of NTSC. Thomson also co-authored the current American high-definition TV standard ATSC.
Why SECAM elsewhere?
The adoption of SECAM in Eastern Europe has been attributed to Cold War political machinations: its use made it impossible for most Eastern Europeans to view television broadcast from outside the Iron Curtain using PAL.
However, remember that PAL and SECAM are just standards for the color subcarrier, used in conjunction with older standards for the base monochrome signals. The names for these monochrome standards are letters, such as M, B/G, D/K, and L. See CCIR, OIRT and FCC (the standardization bodies).
These signals are much more important to compatibility than the color subcarriers. They differ by AM or FM modulation, signal polarisation, relative frequencies within the channel, bandwidth, etc. For example, a PAL D/K TV set will be able to receive a SECAM D/K signal (although in black and white), while it will not be able to receive a PAL B/G signal at all. So even before SECAM came to Eastern European countries, most viewers could not have received Western programs.
Another, speculative political reason is that PAL was originally German, while SECAM came from a country which had better political relations with Eastern Europe after the war.
SECAM varieties
There are three varieties of SECAM:
- French SECAM, used in France and its former colonies
- MESECAM, used in the Middle East
- SECAM D/K, used in the Commonwealth of Independent States and Eastern Europe. (This is simply SECAM used with the D and K monochrome TV transmission standards.)
Problems with the standard
Unlike PAL or NTSC, analog SECAM television cannot easily be edited in its native form. This is related to the limited supply of affordable equipment. Hence, post-production is often done in PAL, with the result transcoded into SECAM at the point of transmission. Reducing the costs of running television stations is one reason for some countries' recent switchovers to PAL.
TVs currently sold in SECAM countries support both SECAM and PAL, and more recently NTSC as well. Although the older analogue camcorders (VHS, VHS-C and 8mm) were produced in SECAM versions, none of the Hi-band models were (S-VHS, S-VHS-C and Hi-8). There are no SECAM Digital camcorders or DVD players. However, this is of dwindling importance: since 1980 most European equipment uses SCART connectors, allowing the transmission of RGB signals between devices. This eliminates the legacy of PAL, SECAM and NTSC color subcarrier standards. Digital equipment does not use these subcarrier standards.
Facetious interpretations of the SECAM acronym
American engineers have been known to claim that SECAM stands for "System Essentially Contrary to the American Method". European non-SECAM countries know that it really means "Shows Every Colour All Murky" – a reference to the reduction in vertical colour resolution. Although the first facetious expansion may have reflected the intentions of the SECAM designers, the second one is (as a contrast with PAL) probably a mistake.
Countries which use or have used SECAM
Afghanistan, Andorra, Armenia, Azerbaijan, Belarus, Benin, Bulgaria, Burkina Faso, Burundi, Cambodia (Kampuchea), Central African Republic, Chad, Congo (Peoples Republic), Corsica, Czech Republic, Djibouti, Egypt, Equatorial Guinea, Estonia, France, French Guiana, French Polynesia, Gabon, Georgia, Greece, Guadeloupe, Hungary, Iran, Iraq, Ivory Coast, Kazakhstan, North Korea, Kyrgyzstan, Latvia, Libya, Lithuania, Luxembourg, Madagascar, Mali, Martinique, Mauritania, Mauritius, Monaco, Mongolia, Morocco, New Caledonia, Niger, Réunion, Romania, Rwanda, Saint-Pierre and Miquelon, Saudi Arabia, Senegal, Serbia, Slovakia, Syria, Tahiti, Tajikistan, Togo, Tunisia, Turkmenistan, Ukraine, Uzbekistan, Vietnam, Wallis Island, Zaire.
Some SECAM countries are in the process of switching to PAL and are broadcasting in both SECAM and PAL formats. The list does not contain certain countries known to have totally switched to PAL.