sign in sign up
<<
Home , Analog television, Colorburst, Color television, Composite video, Dot crawl, Flicker fusion threshold

ANALOG ENCODING FORMATS

NTSC

NTSC is the analog system in use in the and many other countries, including most of the and some parts of East . It is named for the National Television System(s) Committee, the industry-wide standardization body that created it. encodes picture by varying the and/or of the signal. ... The Americas refers collectively to North and , as a relatively recent and less ambiguous alternative to the name America, which may refer to either the Americas (typically in languages other than English, where it is often considered a single continent) or to the United States (in English and...East Asia can be defined in either cultural or geographic terms. ...

History

The National Television Systems Committee was established in 1940 by the Federal Communications Commission (FCC) to resolve the conflicts which had arisen between companies over the introduction of a nationwide analog television system in the U.S. The committee in March 1941 issued a technical standard for and television. This built upon a 1936 recommendation made by the Manufacturers Association (RMA) that used 441 lines. With the advancement of the vestigial technique for that increased available , there was an opportunity to increase the . The NTSC compromised between RCA's desire to keep a 441-line standard (their NBC TV network was already using it) and 's desire to increase it to between 600 and 800, settling on a 525-line transmission. 1940 was a leap year starting on Monday (link will take you to calendar). ... The Federal Communications Commission (FCC) is an independent United States government agency, created, directed, and empowered by Congressional statute. ...1941 was a common year starting on Wednesday (link will take you to calendar). ...This article is about the term as used in media and computing; for more specific uses, see . ...1936 was a leap year starting on Wednesday (link will take you to calendar). ...Single-sideband (SSB) is a refinement of the technique of modulation designed to be more efficient in its use of electrical power and bandwidth. ...Analog Bandwidth is the width, usually measured in , of a frequency band f2 - f1. ...RCA, formerly an initialism for the Radio Corporation of America, is a trademark used by two companies for products descended from that common ancestor: Thomson Consumer Electronics, which manufactures RCA-branded , DVD players, video cassette recorders, direct broadcast satellite decoders, , audio equipment, , and related accessories; and...The 1986 Peacock logo, designed by Chermayeff & Geismar. ...

In January 1950 the Committee was reconstituted, this time to decide about television. In March 1953 it unanimously approved what is now called simply the NTSC standard. The updated standard retained full backwards compatibility with older black and white television sets. 1950 was a common year starting on Sunday (link will take you to calendar). ... 1953 is a common year starting on Thursday. ...

The FCC had briefly approved a different color television system starting in 1950. It was developed by CBS and was incompatible with black and white broadcasts. That system used a rotating color wheel, reduced the number of scanlines from 525 to 405, and increased the rate from 60 to 144 (but had an effective of 24 frames per second). Delay tactics by rival RCA kept the system off the air until mid-1951, and regular broadcasts only lasted a few months before manufacture of CBS-compatible systems was banned by the National Production Authority (NPA). Most of the existing devices were soon destroyed and only two receivers are known to exist today. The CBS system was rescinded by the FCC in 1953 and was replaced later that year by the NTSC color standard, which had been developed with the cooperation of several companies including RCA and Philco. A variant of the CBS system was later used by NASA to broadcast pictures of astronauts from space. first color logo, which debuted in the fall of 1965. ... In the arts of painting, and photography, color theory is a set of basic rules for mixing color to achieve a desired result. ...A scanline is a line on a CRT tube, made up of dots. ...Frame rate, or frame frequency, is the measurement of how quickly an imaging device can produce several consecutive images, called frames.

A third "line sequential" system from Color Television, Incorporated (CTI) was also considered. The CBS and final NTSC systems were called "field sequential" and "dot sequential" systems, respectively.

The first commercially available color NTSC television camera was the RCA TK- 40A, introduced in March 1954. It was replaced later that year by an improved version, the TK-41, which became the standard camera used through much of the . A professional video camera (often called a television camera even though the use has spread) is a high-end device for recording electronic moving images (as opposed to a , that records the images on ). ... The RCA TK-40 is considered to be the first color television camera, initially used for special broadcasts in late 1953, and with the follow-on TK-40A actually becoming the first to be produced in quantity in March 1954. ...1954 was a common year starting on Friday of the Gregorian calendar. ...Events and trends The 1960s was a turbulent decade of change around the world. ...

The NTSC standard has since been adopted by many other countries, for example most of the Americas and . The Americas (sometimes referred to as America) is the area including the land mass located between the Pacific Ocean and the Atlantic Ocean, generally divided into and South America. ...

Technical details

The NTSC format—or more correctly the format; see broadcast television systems—consists of 29.97 interlaced frames of video per second. Each frame consists of 480 lines out of a total of 525 (the rest are used for sync, vertical retrace, and other data such as captioning). The NTSC system interlaces its scanlines, drawing odd-numbered scanlines in odd-numbered fields and even- numbered scanlines in even-numbered fields, yielding a nearly -free image at its approximately 59.94 hertz (nominally 60 Hz / 1.001) refresh frequency. This compares favorably to the 50 Hz of the 625-line PAL and SECAM video formats used in , where 50 Hz is the standard; flicker is more likely to be noticed when using these standards. Interlacing the picture does complicate editing video, but this is true of all formats, including PAL and SECAM. There are several broadcast television systems in use in the world today. ... Interlacing is a method of displaying images on a raster-scanned display device, such as a ray tube (CRT). ...Video is the technology of processing electronic signals representing moving pictures. ...This article is about the unit of time. ...The (or flicker fusion rate) is a concept in the psychophysics of vision. ...The hertz (symbol Hz) is the SI unit of frequency. ...Sine of various ; the lower waves have higher frequencies than those above. ...The refresh rate (or vertical refresh rate, vertical scan rate) is the maximum number of frames that can be displayed on a monitor in a second, expressed in Hertz. ...For other meanings of PAL see PAL (disambiguation). ...SÉCAM (Séquentiel couleur à mémoire, French for sequential colour with memory) is an analog color television system first used in . ...World map showing location of Europe A satellite composite image of Europe Europe is geologically and geographically a peninsula, forming the westernmost part of Eurasia. ...An alternating current (AC) is an electrical current where the magnitude and direction of the current varies cyclically, as opposed to , where the direction of the current stays constant. ...

The NTSC refresh frequency was originally exactly 60 Hz in the black and white system, chosen because it matched the nominal 60 Hz frequency of alternating current power used in the United States. It was preferable to match the screen refresh rate to the power source to avoid interference that would produce rolling bars on the screen. Synchronization of the refresh rate to the power cycle also helped cameras record early broadcasts, as it was very simple to synchronize a film camera to capture one frame of video on each film cell by using the alternating current frequency as a shutter trigger. In the color system the refresh frequency was shifted slightly downward to 59.94 Hz. Synchronization is coordination with respect to time. ... The term kinescope originally referred to a type of early television picture tube. ...Film refers to the celluloid media on which movies are printed Film is a term that encompasses motion pictures as individual projects, as well as the field in general. ...

The mismatch in frame rate between NTSC and the other two video formats, PAL and SECAM, is the most difficult part of video format conversion. Because the NTSC frame rate is higher, it is necessary for video conversion equipment converting to NTSC to interpolate the contents of adjacent frames in order to produce new intermediate frames; this introduces artifacts, and a trained eye can quickly spot video that has been converted between formats. (See also stutter frame.) Frame rate, or frame frequency, is the measurement of how quickly an imaging device can produce several consecutive images, called frames. ... A video format describes how one device sends a video pictures to another device, such as the way that a DVD player sends pictures to a television, or a to a monitor. ...This article is about interpolation in mathematics. ...In film, video production, animation, and related fields, a frame is one of the many still images which compose the complete moving picture. ...This page is about artifacts in science. ...

Color encoding

For backward compatibility with black and white television, NTSC—in this area the terminology NTSC is technically correct—uses a luminance- encoding system invented in 1938 by . Luminance is essentially the original signal, while chrominance carries color information. This allows black and white receivers to display NTSC signals simply by ignoring the chrominance information. In NTSC, chrominance is encoded as two quadrature signals: I (in-phase) and Q (quadrature). The word luminance, a synonym for luminosity, means emitting or reflecting light. ... Chrominance (chroma for short) comprises the two components of a television signal that encode color information. ...Georges Valensi was a French engineer who, in 1938, invented and patented a method of transmitting color images so that they could be received on both color and black & white television sets. ...

To implement this system, NTSC modulates the chrominance signal with a at a frequency of 3.579545 (exactly 315/88) MHz. The subcarrier itself is suppressed in transmission, but is made known by transmitting a sinusoidal reference signal known as , located on the front porch of each scanline, an otherwise unused period between the horizontal synchronization pulse and the actual start of each video line. The colorburst consists of eight to ten cycles of the unmodulated subcarrier at 180° phase. The modulated chrominance is then added to the video signal in any portion of the scanline displaying color. Once properly decoded, the subcarrier's amplitude and its phase in relation to the colorburst's phase determine color, using a system called YIQ. A subcarrier is separate analog or carried on a main radio transmission, which carries extra information such as voice or data. ... Reduced-carrier transmission is an (AM) transmission in which the level is reduced to reduce wasted electrical power. ...Colorburst is a signal used to keep the chrominance subcarrier synchronized in a color television signal. ...In , the front porch is a brief (about 1. ...YIQ is the used in the NTSC television standard. ...

The addition of this subcarrier made necessary the slight downward adjustment in the refresh rate. When NTSC is broadcast over VHF or UHF, it amplitude modulates the VHF or UHF carrier while an is transmitted by frequency modulating a carrier 4.5 MHz higher. If the signal is affected by non- linear , which can happen in many receivers, the 3.58 MHz color carrier may with the sound carrier to produce a dot pattern on the screen. The frame rate was adjusted in such a way that any possibly occurring pattern wouldn't be noticeable. Very (VHF) is the range from 30 MHz ( 10 m) to 300 MHz (wavelength 1 m). ... This article is about the radio frequency. ...Beating is striking more than once, in violence, beating a drum, etc. ...

Another important factor in choosing the new exact frame rate was to make sure that the color signal phase would be shifted exactly 180 degrees for each scanline. There are two reasons why this is important. First, the chroma signal does cause some distortion to older TV sets, especially those that were used at the time of the introduction of color TV and which didn't have notch filters to filter out the chroma information. In addition, early color TV sets (and newer cheap ones) suffer from imperfect luminance and chrominance separation, causing dots to appear near strong-colored edges. These dots are called creepy crawlies or, more commonly, . They are particularly visible along vertical lines in the transmitted video, especially when SMPTE color bars are transmitted. The phase shift makes these dots non-stationary and thus reduces their visibility. The second reason to the phase shift is that it makes it possible to use a comb filter, which allows separating chrominance and luminance information with much better fidelity. While an exact 180 degree phase shift per scanline is not an absolute necessity for a comb filter to work, it makes implementation easier and also gives the best potential quality. This is a lesson that was later forgotten when developing the PAL color coding scheme. This probably didn't seem like a big omission at the time, since comb filters didn't become widely available in NTSC television sets before the 1980's (and, because of huge implementation difficulties, high-end PAL 100 Hz TV sets didn't get comb filters before the late 1990s). Nevertheless, the theoretical groundwork that made comb filters possible was there from the beginning. The dot crawl is the popular name for a visual defect of color analog video standards when signals are transmitted as . ... The SMPTE color bars SMPTE color bars is a type of television test pattern, and is most commonly used in countries where the NTSC video standard is dominant, such as in North America. ...In , a comb filter adds a slightly delayed version of a signal to itself, causing phase cancellations. ...For other meanings of PAL see PAL (disambiguation). ...Events and trends The 1990s are generally classified as having moved slightly away from the more conservative 1980s, but keeping the same mind-set. ...

Transmission modulation scheme

An NTSC as transmitted occupies a total bandwidth of 6 MHz. A guard band, which does not carry any signals, occupies the lowest 250 kHz of the channel to avoid interference between the video signal of one channel and the audio signals of the next channel down. The actual video signal, which is amplitude-modulated, is transmitted between 500 kHz and 5.45 MHz above the lower bound of the channel. The video carrier is 1.25 MHz above the lower bound of the channel. Like any modulated signal, the video carrier generates two , one above the carrier and one below. The sidebands are each 4.2 MHz wide. The entire upper sideband is transmitted, but only 750 kHz of the lower sideband, known as a vestigial sideband, is transmitted. The color subcarrier, as noted above, is 3.579545 MHz above the video carrier, and is quadrature-amplitude-modulated. The highest 250 kHz of each channel contains the audio signal, which is frequency-modulated, making it compatible with the audio signals broadcast by FM radio stations in the 88-108 MHz band. The main audio carrier is 4.5 MHz above the video carrier. Sometimes a channel may contain an MTS signal, which is simply more than one audio signal. This is normally the case when stereo audio and/or signals are used. A is a type of radio station that broadcasts both audio and video to television receivers in a particular area. ... Interference of two circular waves - Wavelength (decreasing bottom to top) and Wave centers distance (increasing to the right). ...Amplitude modulation (AM) is a form of modulation in which the amplitude of a carrier wave is varied in direct proportion to that of a modulating signal. ...Carrier frequency is the fundamental frequency used in both amplitude modulation and i. ...In radio communications, a sideband is of frequencies higher than or lower than the carrier frequency, containing energy as a result of the modulation process. ...Single- sideband modulation (SSB) is a refinement of the technique of amplitude modulation designed to be more efficient in its use of electrical power and bandwidth. ...QAM redirects here; for other uses of that abbreviation, see QAM (disambiguation). ...Frequency modulation (FM) is a form of modulation which represents information as variations in the instantaneous frequency of a carrier wave. ... sound, better known as MTS (often still as BTSC, for the Broadcast Television Systems Committee that created it), is the method of encoding three additional channels of audio into an NTSC-format audio carrier. ...Stereo or stereophony generally refers to dual-channel sound recording and sound reproduction – sound that contains data for more than one speaker simultaneously. ...Second[ary] audio program[ming] (SAP) is an auxiliary audio channel for television that can be broadcast or transmitted both over the air and by cable TV. It is often used for an alternate language (hence giving the facetious Spanish audio program expansion to the acronym), or for the Descriptive...

Countries and territories which use NTSC

North America: , , United States

Central America: , , Bahamas, , , , , , Rica, , , , , , , , , Leeward Islands, , Netherlands Antilles, , , St. Kitts and Nevis, St. Lucia, St. Vincent and the Grenadines, and Tobago, U.S. Virgin Islands

South America: , , , , , , , , (PAL-M system, based on NTSC-M standard but using PAL color encoding)

Asia: Japan, , , , , (Propaganda station aimed at South Korea; domestic broadcasts use PAL), South (Historic; all of Vietnam now uses PAL)

The Pacific: , Diego Garcia, Fiji, , , Micronesia, , , , Samoa

Middle East: South Yemen (Historic; all of Yemen now uses PAL)

PAL

PAL, short for phase-alternating line, phase alternation by line or for phase alternation line, is a colour encoding used in broadcast television systems, used throughout the world except in most of the Americas, some East Asian countries (which use NTSC), parts of the and Eastern Europe, and France (which use SECAM, though most of them are in the process of adopting PAL). PAL was developed in by , working at , and first introduced in 1967. For alternative meanings, see color (disambiguation). ... There are several broadcast television systems in use in the world today. ...The Americas is an alternative name in the English language for the continent of America, to distinguish it from the United States of America, which is often just called America. ...East Asia can be defined in either cultural or geographic terms. ...NTSC is the analog television system in use in the United States and many other countries, including most of the Americas and some parts of East Asia. ...A map showing countries commonly considered to be part of the Middle East The Middle East is a region comprising the lands around the southern and eastern parts of the Mediterranean Sea, a territory that extends from the eastern Mediterranean Sea to the Persian Gulf. ...Eastern Europe is, by convention, that part of Europe from the Ural and Caucasus mountains in the East to an arbitrarily chosen boundary in the West. ...SÉCAM (Séquentiel couleur à mémoire, French for sequential colour with memory) is an analog color television system first used in France. ...Walter Bruch (1908-1990) was a German engineer, famous for inventing the PAL color television system at Telefunken in the early 1960s. ...Telefunken is a German radio- and television company, founded in 1903. ...1967 was a common year starting on Sunday of the Gregorian calendar. ...

Note that French electronics manufacturer Thomson, where Henri de France developed SECAM, later bought Telefunken. Thomson is also behind the RCA brand for consumer electronics products, and RCA created the NTSC color TV standard (before Thomson became involved). Thomson SA (NYSE: TMS)(Euronext: TMM) , formerly known as Thomson Multimedia is a multinational electronics manufacturer and media services provider headquartered in Boulogne, France. ... Henri de France was an influential French television engineer. ...SÉCAM (Séquentiel couleur à mémoire, French for sequential colour with memory) is an analog color television system first used in France. ...Telefunken is a German radio- and television company, founded in 1903. ...Thomson SA (NYSE: TMS)(Euronext: TMM) , formerly known as Thomson Multimedia is a multinational electronics manufacturer and media services provider headquartered in Boulogne, France. ...RCA, formerly an initialism for the Radio Corporation of America, is now a trademark used by two companies for products descended from that common ancestor: Thomson Consumer Electronics, which manufactures RCA-branded televisions, DVD players, video cassette recorders, direct broadcast satellite decoders, camcorders, audio equipment, telephones, and related accessories; and...RCA, formerly an initialism for the Radio Corporation of America, is now a trademark used by two companies for products descended from that common ancestor: Thomson Consumer Electronics, which manufactures RCA-branded televisions, DVD players, video cassette recorders, direct broadcast satellite decoders, camcorders, audio equipment, telephones, and related accessories; and...NTSC is the analog television system in use in the United States and many other countries, including most of the Americas and some parts of East Asia. ...

Technical details

The basics of PAL are quite similar to the NTSC system; the SECAM system, on the other hand, is quite different from both of the others. The name "Phase Alternating Line" describes the way that part of the colour information on the video signal is reversed in phase with each line, which automatically corrects phase errors in the transmission of the signal by canceling them out. (Lines where the color phase is reversed compared to NTSC are often called PAL or phase-alternation lines, which justifies one of the expansions of the acronym, while the other lines are called NTSC lines.) Early PAL receivers relied on the imperfections of the human eye to do that canceling, however this resulted in a comb-like effect on stronger phase errors. Thus, most receivers use a delay line which stores the received color information on each line of display; an average of the color information of the current line and that of the previous line is then used to drive the picture tube. This reduces vertical color resolution compared to the NTSC system, however since the human retina also has a color resolution that is much lower than its brightness resolution, this effect is not visible. NTSC is the analog television system in use in the United States and many other countries, including most of the Americas and some parts of East Asia. ... SÉCAM (Séquentiel couleur à mémoire, French for sequential colour with memory) is an analog color television system first used in France. ...Color is an important part of the visual arts. ...The term delay line has multiple meanings: In : A delay line is a , or equivalent device, used to delay a signal. ...Human eye cross-sectional view. ...

NTSC receivers have a tint control to perform that correction manually. Some engineers jokingly expand NTSC to "Never Twice the Same Colour" while referring to PAL as "Perfect At Last" or "Peace At Last"! However, the alternation of colour information - bars - can lead to picture grain on pictures with extreme phase errors even in PAL systems, causing some engineers to alternately expand PAL to "Picture Always Lousy". NTSC is the analog television system in use in the United States and many other countries, including most of the Americas and some parts of East Asia. ... Since the NTSC color television standard is susceptible to color errors, there is a tint control on NTSC television sets, which allows the image to be corrected. ...NTSC is the analog television system in use in the United States and many other countries, including most of the Americas and some parts of East Asia. ..., in the simplest PAL television video format, is an undesirable artefact in the reception of a television image. ...

The PAL colour system is usually used with a video format that has 625 lines per frame (576 visible lines, the rest being used for other information such as sync data and captioning) and a refresh rate of 25 frames per second, interlaced, such as systems B, G, H, I, and N (see broadcast television systems for the technical details of each format). Some countries in Eastern Europe which formerly used SECAM with systems D and K have switched to PAL while leaving other aspects of their video system the same. (However, some other countries changed completely from SECAM-D/K to PAL-B/G.) In Brazil, PAL is used in conjunction with the 525 line, 29.97 frame/s system M, using (very nearly) the NTSC color subcarrier frequency. Almost all other countries using system M use NTSC. In , and , PAL is used with the standard 625 line system, but again with (very nearly) the NTSC color subcarrier frequency; these variants are called PAL-N and PAL-CN. Recently-manufactured PAL television receivers can typically decode all of these systems, except in some cases PAL-M and PAL-N. Many of them can also receive Eastern European and Middle Eastern SECAM, though usually not French SECAM, unless they are made in France. Many of them can also accept NTSC-M, such as from a VCR or game console, though not usually broadcast NTSC. There are several broadcast television systems in use in the world today. ... Eastern Europe is, by convention, that part of Europe from the Ural and Caucasus mountains in the East to an arbitrarily chosen boundary in the West. ...SÉCAM (Séquentiel couleur à mémoire, French for sequential colour with memory) is an analog color television system first used in France. ...In non-technical use baseband is a description of signals on a transmission medium. ...

When video is transmitted baseband, most of the differences between the "one- letter" systems are no longer significant, other than vertical resolution and frame rate, and in that context, unqualified PAL invariably means 576 lines at 25 frames per second, interlaced, with PAL color. In applications, such as and , even the color encoding is no longer significant; in that context, PAL means only 576 lines at 25 frames per second interlaced, and there is no longer any difference to SECAM.

Cinema are typically recorded at 24 frames per second; when played back at PAL's standard of 25 frames per second, films therefore typically run 4% faster[1] (http://www.michaeldvd.com.au/Articles/PALSpeedUp/PALSpeedUp.asp ). Unlike NTSC's system, this is usually un-noticeable in practice, although as a consequence films shown on video equipment in PAL countries run for 4% less time than their NTSC brothers, despite being otherwise identical. Telecine is the process of transferring motion picture film to a video format, such as television, or a machine used to complete this process. ...

Countries and territories which use PAL B/G or PAL D/K

Europe: , Ascension Island, Austria, Azores, , Bosnia and Herzegovina, Canary Islands, Croatia, , Denmark, , Faroe Islands, Finland, Germany, Gibraltar, , Greenland, , , , Liechtenstein, , , Macedonia, Madeira, Malta, Netherlands, Norway, , , Republic of Ireland, , Serbia and Montenegro, Slovenia, , , Sweden, Switzerland, Tristan da Cunha, , Vatican City

Asia: , Bahrain, , Brunei, (mainland), , Dubai, Gaza & West Bank, , , Israel, Jordan, Kuwait, , , Maldives, Nepal, North Korea, Oman, , Qatar, , Sri Lanka, , , Turkey, United Arab Emirates, Vietnam, Yemen

The Americas: Falkland Islands

Africa: Algeria, Angola, Botswana, Cameroon, Cape Verde, Eritrea, Ethiopia, Gambia, , , Guinea-Bissau, Kenya, Lesotho, , Malawi, Mozambique, Namibia, , Seychelles, Sierra Leone, Somalia, , Sudan, Swaziland, , Uganda, Zambia, ,

Australia and Oceania: , Christmas Island, Cook Island, Easter Island, , Norfolk Island, Papua New Guinea, Solomon Islands, Tonga, Vanuatu

Countries and territories which use PAL-I

Europe: and Ireland Asia: and Macao,

Countries and territories which use PAL-M

Latin America: Brazil (NTSC & PAL-M) Asia: Laos (SECAM & PAL-M).

Countries which use PAL-N or PAL-CN

Latin America: Argentina, Paraguay and Uruguay.

SECAM

SECAM (Sequentiel couleur e memoire, French for "sequential colour with memory") is an analog color television system first used in France. SECAM has been invented by a team lead by Henri de France and working at Thomson. It is historically the first European color television standard.

Technical details

Just as the other color standards adopted for broadcast usage over the world, SECAM is a compatible standard, which means that monochrome television receivers predating its introduction are still able to correctly show the programs, although only in black and white. Because of this compatibility requirement, color standards add a second signal to the basic monochrome signal, and this signal carries the color information, called chrominance or C in short, while the black and white information is called the luminance (Y in short). Old TV receivers only see the luminance, while color receivers process both signals.

Another aspect of the compatibility being not using 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 recycled. This lack of continuity results from the discrete nature of the signal, which is divided into frames and lines. Analog colour systems differ by the way in which empty space is used. In all cases, the colour signal is inserted at the end of the spectrum of the monochrome signal.

In order to be able to separate the color signal from the monochrome one in the receiver, a fixed frequency subcarrier has to be used, this subcarrier 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 colour subcarrier still has to carry a two dimensional signal. Typically the (R) and the (B) information are carried because their signal difference with luminance (R-Y and B-Y) is stronger than that of (G-Y).

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 subcarrier.

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 colour from the preceding line. It uses a delay line, an analog memory device, for the purpose of storing one line of colour information. This justifies the "Sequential, With Memory" name.

Because SECAM transmits only one color at a time, it is free of the color artifacts present in NTSC and PAL and resulting from the combined transmission of both signals.

This means that the vertical color resolution is halved relative to NTSC. It is however not halved compared to PAL. Although PAL does not eliminate half of vertical color information during encoding, it combines colour information from adjacent lines at the decoding stage, in order to compensate for color subcarrier phase errors occurring during the transmission of the Amplitude-Modulated color subcarrier. 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). Since the FM modulation of SECAM's color subcarrier is insensitive to phase (or amplitude) 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 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 suitable to the transmission of only one signal at a time.

Because of the FM modulation, SECAM is free of the dot crawl problem commonly encountered with the other analog standards and first widely noticed with the . Dot crawl can be removed from PAL and NTSC-encoded signals using a comb filter. Such filters are usually only included in high-end displays. Dot crawl patterns (animated checkerboard) are easily visible along vertical lines in DVD menus displayed even by expensive (eg. ) displays if these displays are connected to a signal source (DVD player) using a composite PAL or NTSC connection rather than for example RGB.

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 color information was always supposed to be a cheap and backwards-compatible addition to the monochrome signal, it never had the same horizontal resolution as the monochrome information: the colour subcarrier has always a more limited bandwidth than the luminance signal. Therefore, it was not logical to keep the full color resolution vertically either.

DVD and other formats have perpetuated the implementation of this idea, subsampling colour both horizontally and vertically. Hence, paradoxically, VHS NTSC can have a greater vertical colour resolution than DVD.

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. However, because of the interlacing, vertical resolution is effectively not as great as the number of scan lines. 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. Therefore computer generated text and inserts have to be carefully down-pass filtered to prevent this.

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 chanel (the second network), currently called . A group of four men, all dressed in suits, presumably presenters and network officials, were shown standing in a studio. The image was originally black and white and suddenly switched to colour; one of the people said something along the lines of "now you can see us as we really are".

The first colour 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 USA.

SECAM was later adopted by former French and Belgian colonies, Eastern European countries, the former 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 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, whereas NTSC 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 political machinations: it has been claimed that 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.

These signals are much more important to compatibility than the color . They differ by AM or FM modulation, signal , 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 —and color TV sets were not exactly widespread in the Communist bloc anyway, so the B/W-only reception wasn't actually much of a problem.

Another, speculative political theory 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:

1. French SECAM, used in France and its former colonies 2. MESECAM, used in the Middle East 3. 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).

Around 1983-1984 a new color identification standard has been introduced in order to make more space available inside the signal for adding information (originally according to the standard). Identification bursts have been made per-line (like in PAL) rather than per-picture. Older SECAM TV sets might not be able to display color for today's broadcasts.

Problems with the standard

Unlike PAL or NTSC, analog SECAM television cannot easily be edited in its native analog form. This is because of the FM modulation SECAM is not linear with respect to the input image, so that 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, have the mix applied to the demodulated signals, and be remodulated again. Hence, post- production is often done in PAL, or in component formats, 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 baseband NTSC as well (though not usually broadcast NTSC). Although the older analog camcorders (VHS, VHS-C and 8 mm) 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 domestic video equipment uses SCART connectors, allowing the transmission of RGB signals between devices. This eliminates the legacy of PAL, SECAM and NTSC color subcarrier 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 for broadcast. However, large installed bases of analog professional equipment still exist, particularly in third world countries.

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 Color All Murky" —a reference to the reduction in vertical color 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. Given that the French often take a stance against what they call American cultural imperialism, in favor of French culture, SEAM is jokingly said to also stand for "Systeme elegant Contre les AMericains" (Elegant system against the Americans).

Countries which use or have used SECAM

Afghanistan, , , , , , , , , (Kampuchea), , , Congo (People's Republic), C?te d'Ivoire, Czech Republic, , , , , Estonia, France, , , , , Greece, , , , , , North Korea, , Latvia, Libya, Lithuania, Luxembourg, , , , , , , , , , , North Korea, Poland, Reunion, Romania, , , Saint-Pierre and Miquelon, , , Serbia, Slovakia, Syria, Tahiti, , , , , , , 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.