625 lines

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This article is about the analog standard-definition resolution. For the equivalent digital SD resolution, see 576i.
Analog TV standard by nation: countries using 625-line are in blue.

625-line (or CCIR 625/50) is a late 1940s European analog standard-definition television resolution standard.[1][2] It consists of a 625-line raster, with 576 lines carrying the visible image at 25 interlaced frames per second. It was eventually adopted by countries using 50 Hz utility frequency as regular TV broadcasts resumed after World War II.[3] With the introduction of color television in the 1960s,[4] it became associated with the PAL and SECAM analog color systems.

A similar 525-line system was adopted by countries using 60 Hz utility frequency (like the US). Other systems, like 375-line, 405-line, 441-line, 455-line, and 819-line existed, but became outdated or had limited adoption.

The modern standard-definition digital video resolution 576i is equivalent and can be used to digitize an analogue 625-line TV signal, or to generate a 625-line compatible analog signal.[5]

History

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At the CCIR Stockholm Conference in July 1948 a first 625-line system with an 8 MHz channel bandwidth was proposed by the Soviet Union, based on 1946-48 studies[3] by Mark Krivosheev.[6][7][8][9][10][11][12][13] This was initially known as the I.B.T.O. 625-line system.

At a CCIR Geneva meeting in July 1950, Dr. Gerber (a Swiss engineer), proposed a modified 625-line system using a 7 MHz channel bandwidth - informally known as the "Gerber Standard". The system was based on work by Telefunken and Walter Bruch, and was supported by Belgium, Denmark, Italy, Netherlands, Sweden, and Switzerland.[3]

At a CCIR Geneva meeting in May 1951, the existing VHF broadcast standards were standardized.[3] The older 405-line system was designated CCIR System A, the Gerber Standard was designated System B, the Belgian variant System C, and the I.B.T.O. standard System D.

In the 1960s, with the introduction of UHF broadcasts, new 625-line standards were adopted, again with slightly different broadcast parameters, leading to the creation of Systems G, H, I, K, and L.

Analog broadcast 625-line television standards

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The following International Telecommunication Union standards use 625-lines:

World analog 625-line television systems[14]
ITU System Letter Designation B
[15][16][17][18] 		C
[19][20][21] 		D
[22][21][23][24] 		G
[25] 		H
[25] 		I
[26] 		K
[22][27] 		K1 L
[28][21] 		N
[29][30]
Previous designation Gerber Standard
[15][16][17][18] 		Belgian 625-line system
[19][20][21] 		I.B.T.O. 625-line system
[22][21][23][24] 		TAC System
[31]
Band VHF UHF VHF/UHF UHF VHF/UHF
Introduced 1950 1953 1948 1961 1961 1962 1961 1964 1961 1951
Channel bandwidth (MHz) 7 8 6
Video bandwidth (MHz) 5 6 5 5.5 6 4.2
Vision sound carrier separation (MHz) +5.5 +6.5 +5.5 +5.9996 +6.5 -6.5 +4.5
Vestigial sideband (MHz) 0.75 1.25 0.75 1.25 0.75
Vision modulation (+, -) - + - + -
Sound modulation (AM, FM) FM AM FM AM FM
Frequency of chrominance subcarrier (MHz) 4.43 none 4.43 3.58
Vision/sound power ratio 5:1 8:1
Usual color PAL/SECAM none SECAM/PAL PAL/SECAM PAL SECAM/PAL SECAM PAL
Assumed display device gamma[32][14] 2.8 2.0 2.8

Analog color 625-line television systems

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The following analog television color systems were used in conjunction with the previous standards (identified by a letter after the colour system indication):

  • PAL analog color television system (ex: PAL-B, PAL-D, etc.)
  • SECAM analog color television system (ex: SECAM-D, SECAM-L, etc.)

Digital video

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625-lines is sometimes mentioned when digitizing analog video, or when outputting digital video in a standard-definition analog compatible format.

See also

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References

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  8. ^ On the beginning of broadcast in 625-lines 60 year s ago, 625 magazine (in Russian). Archived 2016-03-04 at the Wayback Machine
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  25. ^ a b Reference Data for Radio Engineers, ITT Howard W.Sams Co., New York, 1977, section 30
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