Editing Analog television (section)

==Development==
{{Main|History of television}}

The earliest systems of analog television were [[mechanical television]] systems that used spinning disks with patterns of holes punched into the disc to scan an image. A similar disk reconstructed the image at the receiver. Synchronization of the receiver disc rotation was handled through sync pulses broadcast with the image information. Camera systems used similar spinning discs and required intensely bright illumination of the subject for the light detector to work. The reproduced images from these mechanical systems were dim, very low resolution and flickered severely.

Analog television did not begin in earnest as an industry until the development of the [[cathode-ray tube]] (CRT), which uses a focused electron beam to trace lines across a [[phosphor]] coated surface. The electron beam could be swept across the screen much faster than any mechanical disc system, allowing for more closely spaced scan lines and much higher image resolution. Also, far less maintenance was required of an all-electronic system compared to a mechanical spinning disc system.  All-electronic systems became popular with households after [[World War II]].

===Standards===
{{Further|Broadcast television systems}}
[[Image:Analog-TV-Systems.jpg|thumb|upright=1.5| Analog television system by nation]]
Broadcasters of analog television encode their signal using different systems. The official systems of transmission were defined by the [[ITU]] in 1961 as: A, B, C, D, E, F, G, H, I, K, K1, L, M and N.<ref>[http://www.itu.int/dms_pub/itu-r/opb/act/R-ACT-RRC.1-1961-PDF-E.pdf Final acts of the European Broadcasting Conference in the VHF and UHF bands. Stockholm, 1961.] {{webarchive |url=https://web.archive.org/web/20130729181525/http://www.itu.int/dms_pub/itu-r/opb/act/R-ACT-RRC.1-1961-PDF-E.pdf |date=29 July 2013 }}</ref> These systems determine the number of scan lines, frame rate, channel width, video bandwidth, video-audio separation, and so on. A color encoding scheme ([[NTSC]], [[PAL]], or [[SECAM]]) could be added to the base monochrome signal.<ref>{{cite web|url=http://www.thinkbox.tv/server/show/conGlossary.252|title=TV Technology PAL|work=Publication date unknown|publisher=Thinkbox|access-date=24 November 2010|archive-url=https://web.archive.org/web/20101205214352/http://thinkbox.tv/server/show/conGlossary.252|archive-date=5 December 2010|url-status=dead}}</ref> Using [[RF modulation]] the signal is then modulated onto a [[very high frequency]] (VHF) or [[ultra high frequency]] (UHF) [[carrier wave]]. Each frame of a television image is composed of [[scan line]]s drawn on the screen. The lines are of varying brightness; the whole set of lines is drawn quickly enough that the human eye perceives it as one image. The process repeats and the next sequential frame is displayed, allowing the depiction of motion.  The analog television signal contains timing and synchronization information so that the receiver can reconstruct a two-dimensional moving image from a one-dimensional time-varying signal.

The first [[commercial television]] systems were [[black-and-white]]; the beginning of [[color television]] was in the 1950s.<ref>{{cite web|url=http://inventors.about.com/library/inventors/blcolortelevision.htm|archive-url=https://archive.today/20120720210830/http://inventors.about.com/library/inventors/blcolortelevision.htm|url-status=dead|archive-date=20 July 2012|title=Color Television History|work=Publication date unknown|publisher=About.com|access-date=24 November 2010}}</ref>

A practical television system needs to take [[luma (video)|luminance]], [[chrominance]] (in a color system), synchronization (horizontal and vertical), and [[audio signal]]s, and broadcast them over a radio transmission. The transmission system must include a means of [[television channel]] selection.

Analog [[broadcast television systems]] come in a variety of frame rates and resolutions. Further differences exist in the frequency and modulation of the audio carrier. The monochrome combinations still existing in the 1950s were standardized by the [[International Telecommunication Union]] (ITU) as capital letters A through N. When color television was introduced, the chrominance information was added to the monochrome signals in a way that black and white televisions ignore. In this way [[backward compatibility]] was achieved.

There are three standards for the way the additional color information can be encoded and transmitted. The first was the American [[NTSC]] system. The European and Australian [[PAL]] and the French and former Soviet Union [[SECAM]] standards were developed later and attempt to cure certain defects of the NTSC system. PAL's color encoding is similar to the NTSC systems. SECAM, though, uses a different modulation approach than PAL or NTSC. PAL had a late evolution called [[PALplus]], allowing widescreen broadcasts while remaining fully compatible with existing PAL equipment.

In principle, all three color encoding systems can be used with any scan line/frame rate combination. Therefore, in order to describe a given signal completely, it is necessary to quote the color system plus the broadcast standard as a capital letter. For example, the United States, Canada, Mexico and South Korea used (or use) [[CCIR System M|NTSC-M]],{{efn|Many of these countries have transitioned or are transitioning to digital}} Japan used [[NTSC-J]],{{efn|Discontinued in 2012, when Japan transitioned to digital (ISDB)}} the UK used [[CCIR System I|PAL-I]],{{efn|Discontinued in 2012, when UK transitioned to digital (DVB-T)}} France used [[CCIR System L|SECAM-L]],{{efn|Discontinued in 2011, when France transitioned to digital (DVB-T)}} much of Western Europe and Australia used (or use) [[CCIR System B|PAL-B]]/[[CCIR System G|G]],{{efn|Many of these transitioned or transitioning to DVB-T as digital television standards}} most of Eastern Europe uses [[CCIR System D|SECAM-D]]/[[CCIR System K|K]] or PAL-D/K and so on. <!-- "used" means for broadcast, (taped TV on) VHS still retains analog PAL or NTSC, and thus they are still hypothetically still in use" indefinetly, and DVDs still support and output possibly analog.  Most though output and input digital only. -->

Not all of the possible combinations exist. NTSC is only used with system M, even though there were experiments with [[CCIR System A|NTSC-A]] ([[405 line]]) in the UK and [[CCIR System N|NTSC-N]] (625 line) in part of South America. PAL is used with a variety of 625-line standards (B, G, D, K, I, N) but also with the North American 525-line standard, accordingly named [[PAL-M]].  Likewise, SECAM is used with a variety of 625-line standards.

For this reason, many people refer to any 625/25 type signal as ''PAL'' and to any 525/30 signal as ''NTSC'', even when referring to digital signals; for example, on [[DVD-Video]], which does not contain any analog color encoding, and thus no PAL or NTSC signals at all.

Although a number of different broadcast television systems are in use worldwide, the same principles of operation apply.<ref>{{cite web| url=http://www.paradiso-design.net/TVsystems_worldwide.html|title=Color subcarrier frequency and TV Standards/TV Systems|work=Publication dates 2002, 2003, 2004, 2005 last updated 2005/12/15|publisher=Paradiso Design|access-date=24 November 2010}}</ref>