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PAL
PAL, short for phase alternation by line is a color encoding used in broadcast television systems in large parts of the world. Other common analogue television systems are SECAM (which is very similar to PAL, and so most countries which currently use SECAM are in the process of adopting PAL) and NTSC. PAL was developed by Walter Bruch at Telefunken in Germany, and the format was first introduced in 1967.
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Technical details
Refresh rate
The basics of PAL and the NTSC system are quite similar; a quadrature amplitude modulated subcarrier (typically at approximately 4.43MHz for PAL, and 3.58MHz for NTSC) carrying the chrominance information is added to the lumuminance video signal to form a composite video baseband signal (CVBS). The SECAM system, on the other hand, uses a frequency modulation scheme on its color subcarrier. The name "Phase Alternating Line" describes the way that the phase of part of the color information on the video signal is reversed with each line, which automatically corrects phase errors in the transmission of the signal by cancelling 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, PAL, and SECAM all have chrominance bandwidth (horizontal color detail) reduced greatly compared to the luminance signal anyway.
Color Encoding
NTSC receivers have a tint control to perform that correction manually. Some engineers jokingly expand NTSC to "Never The Same Color" while referring to PAL as "Perfect At Last"! However, the alternation of color information - Hanover 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". Another expansion is "Pay Another Licence" in reference to the British TV Licence fee.
The PAL color 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 50 interlaced fields per second (or 25 full frames per second), 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 Argentina, Paraguay and Uruguay, 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 for the French market. Many of them can also accept baseband NTSC-M, such as from a VCR or game console, though not usually broadcast NTSC.
The PAL color system (either baseband or with any RF system, with the normal 4.43MHz subcarrier unlike PAL-M) can also be applied to an NTSC-like 525-line (480i) picture to form what is often known as "PAL-60" (sometimes "PAL-60/525"). This is often used in applications such as playing NTSC video tapes on compatible PAL VCRs, playing NTSC DVD Video, and video games, as most modern PAL television sets can handle this kind of signal without too many issues - standard NTSC-3.58 support is less common (though more newer sets support it) and often results in a black-and-white picture when viewed on a PAL TV set. However, this issue (the lack of color, or having to convert the video to PAL-60) is easily solved by using RGB connections through SCART cables, which are very common in Europe.
Transmission modulation scheme
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 digital video applications, such as DVDs and digital broadcasting, 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 films 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]. Unlike NTSC's telecine system, this is usually un-noticeable in practice (except that the soundtrack is slightly higher in pitch), 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.
Countries and territories which use PAL
Europe
United Kingdom, Ireland, Albania, Ascension Island, Austria, Azores, Belgium, Bosnia & Herzegovina, Canary Islands, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Faroe Islands, Finland, Germany, Gibraltar, Greece, Greenland, Hungary, Iceland, Italy, Latvia, Liechtenstein, Lithuania, Luxembourg, Macedonia, Madeira, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia & Montenegro, Slovenia, Slovakia, Spain, Sweden, Switzerland, Tristan da Cunha, Turkey, Vatican City
Asia
Afghanistan, Bahrain, Bangladesh, Brunei, China, Cyprus, Dubai, Gaza & West Bank, Hong Kong, India, Indonesia, Israel, Jordan, Kuwait, Laos[1], Lebanon, Macau, Malaysia, Maldives, Nepal, North Korea, Oman, Pakistan, Qatar, Singapore, Sri Lanka, Syria, Thailand, Turkey, United Arab Emirates, Vietnam, Yemen
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Central and South America
Argentina, Brazil[2], Falkland Islands, Paraguay, Uruguay
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Africa
Algeria, Angola, Botswana, Cameroon, Cape Verde, Eritrea, Ethiopia, Gambia, Ghana, Guinea, Guinea-Bissau, Kenya, Lesotho, Liberia, Malawi, Mozambique, Namibia, Nigeria, Seychelles, Sierra Leone, Somalia, South Africa, Sudan, Swaziland, Tanzania, Tunisia, Uganda, Zambia, Zanzibar, Zimbabwe
Australia and Oceania
Australia, Christmas Island, Cook Island, Easter Island, New Zealand, Norfolk Island, Papua New Guinea, Solomon Islands, Tonga, Vanuatu
References
- The standard that defines the PAL system was published by the International Telecommunications Union in 1998 and has the title Recommendation ITU-R BT.470-6, Conventional Television Systems.
