SECAM


SECAM, also written SÉCAM, is an analog color television system first used in France. It was one of three major color television standards, the others being PAL and NTSC.
All the countries using SECAM are currently in the process of conversion, or have already converted to DVB, the new pan-European standard for digital television. SECAM remained a major standard into the 2000s.
This page primarily discusses the SECAM colour encoding system. The articles on broadcast television systems, and analogue television further describe frame rates, image resolution and audio modulation.
, SECAM, and PAL.

Geographic reach

The standard spread from France to its former African colonies. The system was also selected as the standard for color in the Soviet Union, which began broadcasts shortly after the French, and remained in use in most of those countries that were once part of the Soviet Union. Other countries that selected this standard are Zaire, Tunisia, Surinam, Morocco, Mauricio, Monaco, Lebanon, Republic of Côte d'Ivoire, Hungary, Haiti, Greece, France and Egypt.

History

Development of SECAM began in 1956 by a team led by Henri de France working at Compagnie Française de Télévision. The technology was ready by the end of the 1950s, but this was too soon for a wide introduction. A version of SECAM for the French 819-line television standard was devised and tested, but not introduced. Following a pan-European agreement to introduce color TV only in 625 lines, France had to start the conversion by switching over to a 625-line television standard, which happened at the beginning of the 1960s with the introduction of a second network.
The first proposed system was called SECAM I in 1961, followed by other studies to improve compatibility and image quality.
These improvements were called SECAM II and SECAM III, with the latter being presented at the 1965 CCIR General Assembly in Vienna.
Further improvements were SECAM III A followed by SECAM III B, the adopted system for general use in 1967, and first SECAM broadcast was made in France that year.
Soviet technicians were involved in the development of the standard, and created their own incompatible variant called NIIR or SECAM IV, which was not deployed. The team was working in Moscow's Telecentrum under the direction of :ru:Шмаков, Павел Васильевич|Professor Shmakov. The NIIR designation comes from the name of the Nautchno-Issledovatelskiy Institut Radio, a Soviet research institute involved in the studies. Two standards were developed: Non-linear NIIR, in which a process analogous to gamma correction is used, and Linear NIIR or SECAM IV that omits this process.
SECAM was inaugurated in France on 1 October 1967, on la deuxième chaîne, now called France 2. A group of four suited men—a presenter and three contributors to the system's development—were shown standing in a studio. Following a count from 10, at 2:15 pm the black-and-white image switched to color; the presenter then declared "Et voici la couleur !" In 1967, CLT of Lebanon became the third television station in the world, after the Soviet Union and France, to broadcast in color utilizing the French SECAM technology.
The first color television sets cost 5000 Francs. Color TV was not very popular initially; only about 1500 people watched the inaugural program in color. A year later, only 200,000 sets had been sold of an expected million. This pattern was similar to the earlier slow build-up of color television popularity in the US.
SECAM was later adopted by former French and Belgian colonies, Greece, Cyprus, the Soviet Union and Eastern bloc countries, and Middle Eastern countries. However, with the fall of communism, and following a period when multi-standard TV sets became a commodity, many Eastern European countries decided to switch to the West German-developed PAL system.
Other countries, notably the United Kingdom and Italy, briefly experimented with SECAM before opting for PAL.
Since late 2000s, SECAM is in the process of being phased out and replaced by DVB.

Development

Some 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 unusual decision to adopt positive video modulation for French broadcast signals. The earlier systems System A & the 819-line systems were the only other systems to use positive video modulation. In addition, SECAM development predates PAL. NTSC was considered undesirable in Europe because of its tint problem requiring an additional control, which SECAM and PAL solved. Nonetheless, SECAM was partly developed for reasons of national pride. Henri de France's personal charisma and ambition may have been a contributing factor. PAL was developed by Telefunken, a German company, and in the post-war De Gaulle era there would have been much political resistance to dropping a French-developed system and adopting a German-developed one instead.
Unlike some other manufacturers, the company where SECAM was invented, Technicolor, still sells TV sets worldwide under different brands; this may be due in part to the legacy of SECAM. Thomson bought the company that developed PAL, Telefunken, and today even co-owns the RCA brand —RCA being the creator of NTSC. Thomson also co-authored the ATSC standards which are used for American high-definition television.

The spread of SECAM

The adoption of SECAM in Eastern Europe has been attributed to Cold War political machinations. According to this explanation, East German political authorities were well aware of West German television's popularity and adopted SECAM rather than the PAL encoding used in West Germany. This did not hinder mutual reception in black & white, because the underlying TV standards remained essentially the same in both parts of Germany. However, East Germans responded by buying PAL decoders for their SECAM sets. Eventually, the government in East Berlin stopped paying attention to so-called "Republikflucht via Fernsehen", or "defection via television". Later East German–produced TV sets even included a dual standard PAL/SECAM decoder.
Another explanation for the Eastern European adoption of SECAM, led by the Soviet Union, is that the Russians had extremely long distribution lines between broadcasting stations and transmitters. Long co-axial cables or microwave links can cause amplitude and phase variations, which do not affect SECAM signals.
However, PAL and SECAM are just standards for the color sub carrier, used in conjunction with ITU television broadcast systems for the base monochrome signals, identified with letters such as M, B/G, D/K, and L.
These signals are much more important to compatibility than the color sub carriers are. They differ by AM or FM sound modulation, signal polarization, 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, while it will not be able to decode the sound of a PAL B/G signal. So even before SECAM came to Eastern European countries, most viewers could not have received Western programs. This, along with language issues, meant that in most countries monochrome-only reception did not pose a significant problem for the authorities.

Technical details

Just as with the other color standards adopted for broadcast usage over the world, SECAM is a standard which permits existing monochrome television receivers predating its introduction to continue to be operated as monochrome televisions. Because of this compatibility requirement, color standards added a second signal to the basic monochrome signal, which carries the color information. The color information is called chrominance or C for short, while the black-and-white information is called the luminance or Y for short. Monochrome television receivers only display the luminance, while color receivers process both signals.
Additionally, for compatibility, it is required to use no more bandwidth than the monochrome signal alone; the color signal has to be somehow inserted into the monochrome signal, without disturbing it. This insertion is possible because the spectrum of the monochrome TV signal is not continuous, hence empty space exists which can be utilized. This typical lack of continuity results from the discrete nature of the signal, which is divided into frames and lines. Analog color systems differ by the way in which infrequently used space in the frequency band of the signal is used. In all cases, the color signal is inserted at the end of the spectrum of the monochrome signal, where it causes less visual distortion in the uncommon case that the monochrome signal had significant frequency components overlapping the color signal.
In order to be able to separate the color signal from the monochrome one in the receiver, a fixed frequency sub carrier is used, this sub carrier being modulated by the color signal.
The color space is three-dimensional by the nature of the human vision, so after subtracting the luminance, which is carried by the base signal, the color sub carrier still has to carry a two-dimensional signal. Typically the red and the blue information are carried because their signal difference with luminance is stronger than that of green.
SECAM differs from the other color systems by the way the R-Y and B-Y signals are carried.
First, SECAM uses frequency modulation to encode chrominance information on the sub carrier.
Second, instead of transmitting the red and blue information together, it only sends one of them at a time, and uses the information about the other color from the preceding line. It uses an analog delay line, a memory device, for storing one line of color information. This justifies the "Sequential, With Memory" name.
Because SECAM transmits only one chrominance component at a time, it is free of the color artifacts present in NTSC and PAL resulting from the combined transmission of both signals.
This means that the vertical color resolution is halved relative to NTSC. The later PAL system also displays half the vertical resolution of NTSC. Although PAL does not eliminate half of vertical color information during encoding, it combines color information from adjacent lines at the decoding stage, in order to compensate for "color sub carrier phase errors" occurring during the transmission of the Amplitude/Phase-Modulated color sub carrier. This is normally done using a delay line like in SECAM, but can be accomplished "visually" in cheap TV sets using PAL-S decoders. Because the FM modulation of SECAM's color sub carrier is insensitive to phase errors, phase errors do not cause loss of color saturation in SECAM, although they do in PAL. In NTSC, such errors cause color shifts.
The color difference signals in SECAM are actually calculated in the YDbDr color space, which is a scaled version of the YUV color space. This encoding is better suited to the transmission of only one signal at a time.
FM modulation of the color information allows SECAM to be completely free of the dot crawl problem commonly encountered with the other analog standards. SECAM transmissions are more robust over longer distances than NTSC or PAL. However, owing to their FM nature, the color signal remains present, although at reduced amplitude, even in monochrome portions of the image, thus being subject to stronger cross color even though color crawl of the PAL type doesn't exist.
Though most of the pattern is removed from PAL and NTSC-encoded signals with a comb filter by modern displays, some can still be left in certain parts of the picture. Such parts are usually sharp edges on the picture, sudden color or brightness changes along the picture or certain repeating patterns, such as a checker board on clothing. Dot crawl patterns can be completely removed by connecting the display to the signal source through a cable or signal format different from composite video or a coaxial cable, such as S-Video, which carries the chroma signal in a separate band all its own, leaving the luma to use its entire band, including the usually empty parts when they are needed. FM SECAM is a continuous spectrum, so unlike PAL and NTSC even a perfect digital comb filter could not entirely separate SECAM Colour and Luminance.
The idea of reducing the vertical color resolution comes from Henri de France, who observed that color information is approximately identical for two successive lines. Because the color information was designed to be a cheap, backwards compatible addition to the monochrome signal, the color signal has a lower bandwidth than the luminance signal, and hence lower horizontal resolution. Fortunately, the human visual system is similar in design: it perceives changes in luminance at a higher resolution than changes in chrominance, so this asymmetry has minimal visual impact. It was therefore also logical to reduce the vertical color resolution.
A similar paradox applies to the vertical resolution in television in general: reducing the bandwidth of the video signal will preserve the vertical resolution, even if the image loses sharpness and is smudged in the horizontal direction. Hence, video could be sharper vertically than horizontally. Additionally, transmitting an image with too much vertical detail will cause annoying flicker on television screens, as small details will only appear on a single line, and hence be refreshed at half the frequency. Computer-generated text and inserts have to be carefully low-pass filtered to prevent this.
The latest European efforts towards an analog standard, resulting in MAC systems, still used the sequential color transmission idea of SECAM, with only one of time-compressed U and V components being transmitted on a given line. The D2-MAC standard enjoyed some short real market deployment, particularly in northern European countries. To some extent, this idea is still present in 4:2:0 digital sampling format, which is used by most digital video medias available to the public. In this case, however, color resolution is halved in both horizontal and vertical directions thus yielding a more symmetrical behavior.

SECAM varieties

L, B/G, D/K, H, K, M (broadcast)

There are six varieties of SECAM:
  1. French SECAM
  2. : French SECAM is used only in France, Luxembourg and Tele Monte-Carlo Transmitters in the south of France.
  3. SECAM-B/G
  4. :SECAM-B/G is/was used in parts of the Middle East, former East Germany, Greece and Cyprus
  5. SECAM-D/K
  6. : SECAM-D/K is used in the Commonwealth of Independent States and parts of Eastern Europe although most Eastern European countries have now migrated to other systems.
  7. SECAM-H
  8. : Around 1983–1984 a new color identification standard was introduced in order to make more space available inside the signal for adding teletext information. Identification bursts were made per-line rather than per-picture. Very old SECAM TV sets might not be able to display color for today's broadcasts, although sets manufactured after the mid-1970s should be able to receive either variant.
  9. SECAM-K
  10. : France also introduced the SECAM standard to its dependencies. However, the SECAM standard used in France's overseas possessions was slightly different from the SECAM used in Metropolitan France. The SECAM standard used in Metropolitan France used the SECAM-L and a variant of the channel information for VHF channels 2-10. French overseas possessions and many French-speaking African countries use the SECAM-K1 standard and a mutually incompatible variant of the channel information for VHF channels 4-9.
  11. SECAM-M
  12. : Around 1970–1991, SECAM-M was used in Cambodia and Vietnam.

    MESECAM (home recording)

MESECAM is a method of recording SECAM color signals onto VHS or Betamax video tape. It should not be mistaken for a broadcast standard.
"Native" SECAM recording was originally devised for machines sold for the French market. At a later stage, countries where both PAL and SECAM signals were available, such as the USSR, developed a cheap method of converting PAL video machines to record SECAM signals also using the PAL circuitry. A tape produced by this method is not compatible with "native" SECAM tapes as produced by VCRs in the French market. It will play in black and white only, the color is lost. So the world is left with two different incompatible standards for recording SECAM on video cassette.
Although being a workaround, MESECAM is much more widespread than "native" SECAM. It has been the only method of recording SECAM signals to VHS in almost all countries that ever used SECAM, including as mentioned the Middle East and all countries in Eastern Europe. "Native" SECAM recording is only used in France and adjacent countries. Most VHS machines advertised as "SECAM capable" outside France can be expected to be of the MESECAM variety only.

Technical details

On VHS tapes, the luminance signal is recorded FM-encoded but the PAL or NTSC chrominance signal is too sensitive to small changes in frequency caused by inevitable small variations in tape speed to be recorded directly. Instead, it is first shifted down to the lower frequency of 630 kHz, and the complex nature of the PAL or NTSC sub carrier means that the down conversion must be done via heterodyning to ensure that information is not lost.
The SECAM sub carriers on the other hand, consisting of two simple FM signals at 4.41 MHz and 4.25 MHz, do not need this processing. The VHS specification for "native" SECAM recording specifies that they be divided by 4 on recording to give sub carriers of approximately 1.1 MHz and 1.06 MHz, and multiplied by 4 on playback. A true dual-standard PAL and SECAM video recorder therefore requires two color processing circuits, adding to complexity and expense. Since some countries in the Middle East use PAL and others use SECAM, the region has adopted a shortcut, and uses the PAL mixer-down converter approach for both PAL and SECAM. This works well and simplifies VCR design.
Many PAL VHS recorders, with MESECAM, have had their analog tuner modified in French-speaking western Switzerland. The original tuner in those PAL recorders allows only PAL-B/G reception. The Swiss importers added a little circuit, with a specific IC, for the French SECAM-L standard; the tuner thus became multistandard, but the VCR recorded French broadcasts, in MESECAM. Such tapes are played in black and white on "native" SECAM VCRs, and native SECAM tapes are also played in B/W in these modified tuner VCRs. A specific stamp was added on the machines saying "PAL+SECAM".
However some special VHS video recorders are available which can allow viewers the flexibility of enjoying PAL-M recordings using a standard PAL color TV, or even through multi-system TV sets. Video recorders like Panasonic NV-W1E, AG-W2, AG-W3, NV-J700AM, Aiwa HV-MX100, HV-MX1U, Samsung SV-4000W and SV-7000W feature a digital TV system conversion circuitry.

Disadvantages

Unlike PAL or NTSC, analog SECAM programming cannot easily be edited in its native analog form. Because it uses frequency modulation, SECAM is not linear with respect to the input image, so electrically mixing two SECAM signals does not yield a valid SECAM signal, unlike with analog PAL or NTSC. For this reason, to mix two SECAM signals, they must be demodulated, the demodulated signals mixed, and are remodulated again. Hence, post-production is often done in PAL, or in component formats, with the result encoded or 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.
Most TVs currently sold in SECAM countries support both SECAM and PAL, and more recently composite video NTSC as well. Although the older analog camcorders were produced in SECAM versions, none of the 8 mm or Hi-band models recorded it directly. Camcorders and VCRs of these standards sold in SECAM countries are internally PAL. The result could be converted back to SECAM in some models; most people buying such expensive equipment would have a multistandard TV set and as such would not need a conversion. Digital camcorders or DVD players do not accept or output a SECAM analog signal. However, this is of dwindling importance: since 1980 most European domestic video equipment uses French-originated SCART connectors, allowing the transmission of RGB signals between devices. This eliminates the legacy of PAL, SECAM, and NTSC color sub carrier standards.
In general, modern professional equipment is now all-digital, and uses component-based digital interconnects such as CCIR 601 to eliminate the need for any analog processing prior to the final modulation of the analog signal for broadcast. However, large installed bases of analog professional equipment still exist, particularly in third world countries.

Countries and territories that use SECAM

This is a list of nations that currently authorize the use of the SECAM standard for television broadcasting. Nations that have moved to PAL or DVB-T are listed separately.
SECAM users

Migration from SECAM to PAL

Europe

The Slovakia, Hungary and the Baltic countries also changed their underlying sound carrier standard from D/K to B/G which is used in most of Western Europe, to facilitate use of imported broadcast equipment. This required viewers to purchase multistandard receivers though. The other countries mentioned kept their existing standards.

Migration from SECAM to DVB-T