PAL
PAL, short for Phase Alternating 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.
History of the PAL standard
In the 1950s, when the Western European countries were planning to establish colour television, they were faced with the problem that the already existing American NTSC standard wouldn't fit the 50 Hz AC frequency of the European power grids. In addition to that NTSC demonstrated several weaknesses, including colour tone shifting under less-than-ideal transmission conditions, for these reasons the development of the SECAM and PAL standards began. The goal was to provide a colour TV standard with a picture frequency of 50 fields per second (50 Hertz), and sporting a better colour picture than NTSC.
PAL was developed by Walter Bruch at Telefunken in Germany. The format was first unveiled in 1963, with the first broadcasts beginning in the United Kingdom and Germany in 1967.[1]
Telefunken was later bought by the French electronics manufacturer Thomson. Thomson also bought the Compagnie Générale 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 (576i, principally European) television system, and to differentiate from a 525-line/60 Hz (480i, 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 the European disks do not have PAL composite colour. NTSC, by contrast does define the video line and frame format.
Technical details
The basics of PAL and the NTSC system are very similar; a quadrature amplitude modulated subcarrier carrying the chrominance information is added to the luminance video signal to form a composite video baseband signal (CVBS*). The frequency of this subcarrier is typically 4433618.75 Hz (approximately 4.43 MHz) for PAL, compared to approximately 3.58 MHz for NTSC. 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 larger phase errors. Thus, most receivers now use a chrominance delay line, which stores the received colour information on each line of display; an average of the colour information from the previous line and the current line is then used to drive the picture tube. The effect is that phase errors result in saturation changes, which are less objectionable than the equivalent hue changes of NTSC. A minor drawback is that the vertical colour resolution is poorer than the NTSC system's, but since the human eye also has a colour resolution that is much lower than its brightness resolution, this effect is not visible. In any case, NTSC, PAL and SECAM all have chrominance bandwidth (horizontal colour detail) reduced greatly compared to the luminance signal.
For a 1:1 pixel aspect (square pixels) on a 50 Hz interlaced PAL signal the pixel rate should be 14.75 MHz.
The 4.43361875 MHz frequency of the colour carrier is a result of 283.75 colour clock cycles per line plus a 25 Hz offset to avoid interferences. Since the line frequency is 15625 Hz, the colour carrier frequency calculates as follows: 4.43361875 MHz = 283.75 * 15625 Hz + 25 Hz.
- CVBS is an acronym, but it doesn't stand for "composite video baseband signal", CVBS actually stands for (C)hroma, (V)ideo, (B)urst, and (S)ync; which are the four basic components of a composite video signal. That's why it's called "composite".
PAL vs. NTSC
Because the PAL format has greater resolution than NTSC, it is generally accepted as being of higher quality.[2] NTSC receivers have a tint control to perform colour correction manually. If this isn't adjusted correctly, the colours will be faulty. The PAL standard automatically removes hue errors by utilizing phase alternation of the colour signal (see technical details), so a tint control is unnecessary.
However, the alternation of colour information — Hanover bars — can lead to picture grain on pictures with extreme phase errors even in PAL systems. Usually such extreme phase shifts do not occur; this effect will usually be observed when the transmission path is poor, typically in built up areas or where the terrain is unfavourable. The effect is more noticeable on UHF signals than VHF as VHF signals tend to be more robust.
A PAL decoder can be seen as a pair of NTSC decoders:
- PAL can be decoded with two "NTSC" decoders.
- By switching between the two NTSC decoders every other line it is possible to decode PAL without a phase delay line or two phase-locked loop (PLL) circuits.
- This works because one decoder receives a colour sub carrier with negated phase in relation to the other decoder. It then negates the phase of that sub carrier when decoding. This leads to smaller phase errors being cancelled out. However a delay line PAL decoder gives superior performance. Some Japanese TVs originally used the dual NTSC method to avoid paying royalty to Telefunken.
- PAL and NTSC have slightly divergent colour spaces, but the colour decoder differences here are ignored.;
- PAL supports SMPTE 498.3 while NTSC is compliant with EBU Recommendation 14.
- The issue of frame rates and colour sub carriers is ignored in this technical explanation. These technical details play no direct role (except as subsystems and physical parameters) to the decoding of the signal.
Multisystem PAL support and "PAL 60"
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 rarely French broadcast SECAM (because France uses the unique positive video modulation), unless they are made for the French market. They will correctly display plain CVBS or S-video SECAM signals. Many can also accept baseband NTSC-M, such as from a VCR or game console, though not usually broadcast NTSC.
Many newer Video Cassette recorders (and Region 2 DVD players) sold in Europe can play back NTSC tapes/discs. When operating in this mode most of them don't output a true (625/25) PAL signal but rather a hybrid of PAL and NTSC known as "PAL 60" (or "pseudo PAL") with "60" standing for 60Hz, instead of 50Hz. Some video game consoles also output a signal in this mode. Most newer television sets can display such a signal correctly but some will only do so (if at all) in black and white and/or with flickering/foldover at the bottom of the picture, or picture rolling (it can be noted, however, that many analog-era TV sets can receive the picture by means of adjusting the V-Hold and V-Height knobs — assuming they have them). Very few TV tuner cards or video capture cards will support this mode (a small number can, although software/driver modification is usually required and the manufacturers specs are usually unclear). A "PAL 60" signal is similar to an NTSC (525/30) signal but with a PAL chrominance subcarrier at 4.43 MHz (instead of 3.58) and with the PAL-specific phase alternation of the red colour difference signal between the lines.
PAL-M standard (Brazil)
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. Exact colour subcarrier frequency of PAL-M is 3.575611 MHz
- Almost all other countries using system M use 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"). PAL-M (a broadcast standard) however should not be confused with "PAL-60" (a video playback system — see above).
PAL-Nc
In Argentina, the PAL-Nc (combination N) variant is used. The same 625-line system / 50 fields per second as PAL-G,D,G,H, and I is used.
PAL-N
In Paraguay and Uruguay, PAL is used with the standard 625 line/50 fields per second system, but again with (very nearly) the NTSC colour subcarrier frequency (3.582056 MHz); this variation is called PAL-N.
- PAL-N should not be viewed as wildly incompatible versions of the PAL system, only the choice of colour subcarrier is different.
- A VHS recorded off TV (or released) in Europe will play in colour on any PAL-N VCR and PAL-N TV in Argentina, Paraguay, and Uruguay. Likewise, any tape recorded in Argentina or Uruguay off a PAL-N TV broadcast, can be sent to anyone in European countries that use PAL (and Australia/New Zealand, etc) and it will display in colour. This has been very convenient for video collectors in the past.
- In all of South America, DVDs are released in NTSC, Region 4.
People in Uruguay, Argentina and Paraguay usually own TV sets that also display NTSC-M, in addition to PAL-N of course. Direct TV broadcasts in NTSC-M for North, Central and South America so this is very convenient too. Most DVD players sold in Argentina, Uruguay And Paraguay also play PAL discs. However this is usually output in the European variant (colour subcarrier frequency 4.433618 MHz) so people who own a TV set that only works in PAL-N (plus NTSC-M in most cases) will have to watch those PAL DVD imports in black and white, as the colour subcarrier frequency in the TV set is the PAL-N variation, 3.582056 MHz. Some DVD players (usually lesser known brands) include an internal transcoder and the signal can be output in NTSC-M, with some video quality loss because of the systems conversion from a 625/50 PAL DVD disc to the output in NTSC-M 525/60. A few DVD players sold in Argentina and Uruguay allow to output the signal in NTSC-M, PAL, or PAL-N. In that case, a PAL disc (imported from Europe) can be played back on a PAL-N TV. Because there is no fields/lines conversion, quality is excellent.
Extended features of the PAL specification such as teletext are implemented quite differently in PAL-N. PAL-N supports a modified 608 closed captioning format that is designed to ease compatibility with NTSC originated content carried on line 18, and a modified teletext format that can occur several lines.
PAL L
The PAL L standard uses the System L video standard, which is the same as PAL B/G/H (625 lines, 50 Hz field rate, 15.625 kHz line rate) except that it uses 6 MHz video bandwidth rather than 5.5 MHz, lifting the audio subcarrier to 6.5 MHz. When System L is used with SECAM, the audio carrier is amplitude modulated, but when used with PAL, the more usual FM sound system is usually used. The sound offset in B and G is +5.5 whereas in L its +6.5. In layman's language, PAL-L is PAL-BG with positive and AM sound modulation. An 8 MHz channel spacing is used with PAL L,rather than the 7.5 MHz channels usually used with PAL B/G/H.
PAL L is used on some hotel internal distribution systems, as well as other public display and plant television systems. It is not used by any national TV networks. One example of a Tv with PAL-L support is Thomson 24WK25.
All PAL systems interoperable except PAL-M (525/60)
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 (i.e. 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 European countries have changed completely from SECAM-D/K to PAL-B/G.[citation needed]
On RF (i.e. via a Modulator or TV Aerial) the difference between I, D/H and B/G is audio. These use different audio subcarriers, so with mismatch on Modulator Settings or an imported TV there will be perfectly normal Colour Video, but possibly no audio. Some TVs and VHS tuners have multiple filters in parallel or switched for the 6 MHz, 5.5 MHz, 6.5 MHz or 4.5 MHz sound carriers. Nicam is an additional 6.5 MHz offset carrier carrying stereo digitally, on 6.0 MHz PAL I systems. Germany particularly uses two separate FM sound carriers on PAL B/G. (Stereo FM Radio uses a mono signal with a DSBSC L-R audio centered on 38 kHz with a 19 kHz pilot to aid decoding. Hence the German Zweiton and Nicam both give better performance than FM Radio).
Baseband interoperability (analog)
When PAL video is transmitted via baseband (via consumer device cables, not RF), most of the differences between the "one-letter" systems are no longer significant, other than vertical resolution and frame rate.
In this context, unqualified PAL invariably means
- 576 lines
- 25 frames per second
- interlaced video
- with PAL colour (4.43 MHz or 3.58 MHz (PAL-N & PAL-NC))
- FM audio (mono) as only French SECAM uses AM modulation for audio
- mono or stereo audio if sent via connector cables between devices
Modulation for TVRO transmission
PAL when it is transmitted for TVRO viewing is transmitted substantially differently from terrestrial transmission.
Full transponder mode (e.g. 72 MHz)
- Luma signal is FM modulated, but with a 50Hz dithering signal to spread out energy over the transponder.
- Chroma is phase modulated.
- An FM subcarrier of 6.50 or 6.65 MHz is added for mono sound.
- Other FM subcarriers (usually 7.02, 7.20, 7.38, 7.56, 7.74 and 7.92 MHz) are added for a true stereo service and can also carry multi-lingual sound and radio services. These additional subcarriers are normally narrower bandwidth than the main mono subcarrier and are companded using Panda 1 or similar to preserve the signal to noise ratio.
- Data subcarrers may also be added.
Half transponder mode (e.g. 36 MHz)
- all of the above is done, but signal is bandwidth limited to 18 MHz
- the bandwidth limiting does not affect audio subcarriers
Baseband interoperability (digital)
In digital video applications, such as DVDs and digital broadcasting, colour encoding is no longer significant; in that context, PAL means only
- 576 lines
- 25 frames/50 fields {second}
- interlaced video
- PCM audio (baseband)
There is no longer any difference (in the digital domain) between PAL and SECAM. Digital video uses its own separate colour space, so even the minor colour space differences between PAL and SECAM become moot in the digital domain.
Use with progressive sources
When PAL is used to transmit content which was originally composed of 25 progressive full frames per second, the odd field of the frame is transmitted first. This is opposite to NTSC. Systems which recover progressive frames, or transcode video should ensure that this 'Field Order' is obeyed, otherwise the recovered frame will consist of a field from one frame and a field from an adjacent frame, resulting in 'comb' interlacing artifacts.
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% faster. This also applies to most TV series that are shot on film or digital NTSC 24p.[3] 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% shorter than the original film as well as the equivalent NTSC telecined video. Depending on the sound system in use, it also slightly increases the pitch of the soundtrack by 70.67 cent, which is about .66 of a semitone. More recently, digital conversion methods have used algorithms which preserve the original pitch of the soundtrack, although the frame rate conversion still results in faster playback.
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.[4] This is not an issue on modern upconverting DVD players and PCs, as they play back 23.97fps-encoded video at its true frame rate, without 3:2 pulldown.
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. However, this method involves resampling the soundtrack(s), which results in a slight decrease in audio quality.
Countries and territories using PAL
Over 120 countries and territories use or once used the PAL system. Most of these are currently converting to DVB-T.
PAL B, G, D, H or I
PAL-M
PAL-N and PAL-NC
Countries and territories that once used PAL
Finland (switched to DVB-T)
Netherlands (switched to DVB-T)
See also
- PALplus
- Broadcast television systems
- Moving image formats
- Oldest television station
- Digital television
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
- ^ PAL vs NTSC
- ^ PAL speedup
- ^ 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".
External links
- More information about TV standards
- Review of the different refresh rates of PAL, NTSC and motion picture films
- Australian VHF/UHF PAL B/G Television System Datasheet
| Digital Video Resolutions | ||||||||
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| Designation |
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| Low; MP@LL |
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| Standard; MP@ML |
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| Enhanced |
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| High; MP@HL |
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| This table illustrates total horizontal and vertical pixel resolution via box size. It does not accurately reflect the screen shape (aspect ratio) of these formats, which is either 4:3 or 16:9. | ||||||||
| Broadcast Video Formats | |
|---|---|
| Analog broadcast | 525 lines: NTSC •
NTSC-J • PAL-M
625 lines: PAL • PAL-N • PALplus • SECAM Defunct systems: Pre-1940 • 405 lines • 819 lines • Baird-Nipkow • MAC • MUSE Multichannel audio: BTSC (MTS) • NICAM-728 • Zweiton (A2, IGR) • EIAJ Hidden signals: Captioning • Teletext • CGMS-A • GCR • PDC • VBI • VEIL • VITC • WSS • XDS |
| Digital broadcast | Interlaced: SDTV (480i, 576i) •
HDTV (1080i)
Progressive: LDTV (240p, 288p, 1seg) • EDTV (480p, 576p) • HDTV (720p, 1080p) Digital TV standards (MPEG-2):ATSC, DVB, ISDB, DMB-T/H Digital TV standards (MPEG-4 AVC):DMB-T/H,DVB,SBTVD,ISDB (1seg) Multichannel audio: AAC ( |
| Technical issues | 14:9 • MPEG transport • Standards conversion • Video processing • VOD • HDTV blur |
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