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PAL
- For other meanings of "PAL" see PAL (disambiguation).
PAL, short for phase-alternating line, phase alternation by line or phase alternation line, is a colour encoding system used in broadcast television systems in large parts of the world. Other common analogue television systems are SECAM and NTSC. PAL was developed by Walter Bruch at Telefunken in Germany, and the format was first introduced in 1967. [1]
Telefunken was later bought by the French electronics manufacturer Thomson. Thomson also bought the Compagnie Generale de Télévision where Henri de France developed SECAM, historically the first European colour television standard. Thomson nowadays also co-owns the RCA brand for consumer electronics products, which created the NTSC colour TV standard before Thomson became involved.
The term "PAL" is often used informally to refer to a 625-line/50 Hz (principally European) television system, and to differentiate from a 525-line/60 Hz (principally North American/Central American/Japanese) "NTSC" system. Accordingly, DVDs are labelled as either "PAL" or "NTSC" (referring informally to the line count and frame rate) even though technically neither of them have encoded PAL or NTSC composite colour.
Technical details
The basics of PAL and the NTSC system are very similar; a quadrature amplitude modulated subcarrier (typically at approximately 4.43 MHz for PAL, and 3.58 MHz for NTSC) carrying the chrominance information is added to the luminance video signal to form a composite video baseband signal (CVBS). The SECAM system, on the other hand, uses a frequency modulation scheme on its colour subcarrier. The name "Phase Alternating Line" describes the way that the phase of part of the colour 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 colour 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 colour information on each line of display; an average of the colour information of the current line and that of the previous line is then used to drive the picture tube. This reduces vertical colour resolution compared to the NTSC system, however since the human retina also has a colour resolution that is much lower than its brightness resolution, this effect is not visible. NTSC, PAL, and SECAM all have chrominance bandwidth (horizontal colour detail) reduced greatly compared to the luminance signal anyway.
NTSC receivers have a tint control to perform that correction manually. Some engineers jokingly expand NTSC to "Never Twice the Same Colour" or "Not the Same Colour" while referring to PAL as "Perfect At Last", "Peace At Last", or "Pay for Additional Luxury"! However, the alternation of colour 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" or "Pretty Awful Looking". Another expansion is "Pay Another Licence" in reference to the British television licence fee which is higher for colour sets.
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 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 colour 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 colour subcarrier frequency (3.58 MHz); these variants are called PAL-N and PAL-NC. 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 colour system (either baseband or with any RF system, with the normal 4.43 MHz 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" or "Pseudo PAL"). 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 recent 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 colour, 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.
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 colour. In digital video applications, such as DVDs and digital broadcasting, even the colour 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 SÉCAM.
PAL speed-up
Motion pictures are typically shot on film at 24 frames per second. When telecined and played back at PAL's standard of 25 frames per second, films run 4.2% faster. [1] Unlike NTSC's telecine system, which uses 3:2 pulldown to convert the 24 frames per second to the NTSC frame rate, PAL results in the telecined video running 4.2% shorter than the original film as well as the equivalent NTSC telecined video. It also increases the pitch of the soundtrack by 70.67 cent — ⅔ of a semitone, which people with absolute pitch will notice immediately.
However, some movie enthusiasts prefer PAL speed-up over NTSC's 3:2 pulldown, because the latter results in telecine judder, a visual distortion not present in PAL sped-up video. [2]
Software which corrects the speed-up is available for those viewing PAL DVD films on their computers, WinDVD's "PAL TruSpeed" being the most ubiquitous. This method results in a slight decrease in audio quality.
Hardware is also available to correct this effect. Tenlab is the manufacturer of Video Standard Converters, equipment that is used to convert PAL and other formats to NTSC. This is connected between the video source and display using standard video cables.
Countries and territories that use PAL B, G, D or K
Europe
Asia
Africa
Oceania
Countries and territories that use PAL-I
Europe
Asia
The Americas
Africa (all both VHF and UHF)
Countries and territories that use PAL-M
Latin America
Asia
Countries that use PAL-N or PAL-NC
Latin America
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
- ^ DVDLard states "the majority of authorities on the subject favour PAL over NTSC for DVD playback quality". Also DVD reviewers often make mention of this cause. For example, in his PAL vs. NTSC article, the founder of MichaelDVD says "Personally, I find {3:2 pulldown} all but intolerable and find it very hard to watch a movie on an NTSC DVD because of it." In the review of Frequency, one of his reviewers mentions "because of the 3:2 pull-down artefacts that are associated with the NTSC format (...) I prefer PAL pretty much any day of the week".
See also
External links
Digital video resolutions
| Designation |
Usage examples |
Definition (lines) |
Rate (Hz) |
| Interlaced (fields) |
Progressive (frames) |
| Low; MP@LL |
LDTV, VCD |
240; 288 (SIF) |
|
24, 30; 25 |
| Standard; MP@ML |
SDTV, SVCD, DVD, DV |
480 (NTSC, PAL-M); |
60; |
24, 30; |
| 576 (PAL, SECAM) |
50 |
25 |
| Enhanced |
EDTV |
480; 576 |
|
60; 50 |
| High; MP@HL |
HDTV, HD DVD, BD, HDV |
720 |
|
24, 25, 30, 50, 60 |
| 1080 |
50, 60 |
24, 25, 30 |
 |
| This table illustrates total horizontal and vertical detail via box size. It does not accurately reflect the screen shape (aspect ratio) of these formats, which is always stretched or squeezed to 4:3 or 16:9. The table assumes an average vertical detail loss of .75x due to interlace. The actual loss is variable due to content, motion, opinion on acceptable levels of flicker, and possible success of deinterlacing. 1920 × 1080i is not included because all common use of 1080i is filtered to 1440 or less. |
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