(Responses from: Steve McKinty: (email@example.com))
NTSC: National Television Standards Committee PAL: Phase Alternate Line SECAM: SEquential Couleur Avec Memoire (Sequential colour with memory) There are other differences though. Strictly they are just different colour systems, but most countries which use PAL have 625 lines in a picture and send 25 full pictures/second, most NTSC countries have 525 lines and send 30 full pictures/second (mostly for historical rather than technical reasons). That complicates things.
The first serious TV experimenting was done in several countries around the period 1900-1930, mostly black & white. The BBC started a regular service in 1936, other countries followed soon after, but since the technology was developing very rapidly there were always improvements being made. The BBC started with 405 lines, the US started a service a couple of years later with 525, by the time other European countries started the technology allowed 625 lines. France even tried 819 lines. All those system were black & white, but people wanted to have colour. During the 1940's much of Europe was at war, and technological development for entertainment slowed down, but in the US they were able to continue and devised a colour system which was compatible with the existing black & white one. By compatible I mean that a black & white TV got a black & white picture, a colo(u)r one got a colour picture. No need to make people throw away their B&W TVs. This system was endorsed by the American National Television Standards Committee, and was named after it => NTSC. After the war other countries started to look at colour. NTSC was a very clever system, but it had some flaws. Engineers in various countries tried to improve on it, and Telefunken in Germany came up with a simple modification which improved colour stability. It was named PAL because they reversed the Phase of the colour signal on Alternate Lines. At the same time Henri de France, in France, fixed the same flaw in a different way. His design (SECAM) needed a memory inside the set which made it more expensive. PAL gave as good a result, so most countries opted for that. France stayed with SECAM, possibly because in the De Gaulle era of the 50's memories of German occupation were still fresh, and dropping a French system in favour of a German one would have been unpopular. Rumour has it that the French government subsidized Thompson to make memory affordable. Since Britain went PAL, France went SECAM, and the US went NTSC, any colonies or dependencies of those countries tended to get the same system. India/Pakistan got PAL, Algeria got SECAM, and since the US helped rebuild Japan after WW2 it got NTSC, etc.
To squeeze a colour signal into the same space as a black & white one, and stay compatible, the NTSC designers separated the colour and brightness information. The human eye is less sensitive to colour, so they were able to reduce the bandwidth of that signal (make it take up less space in each channel), 'hiding' it at the high-frequency end of the video. That meant they didn't need to make the channels bigger, and incompatible. To do that, they used the fact that you can represent most colours with a combination of Red, Green and Blue. If you film a scene with three cameras, one for each colour, then add all the outputs together you get a black & white image. This signal is called luminance, usually represented by 'Y'. Mathematically Y = R + G + B. (Actually, not all the contributions are equal). They then transmitted the Y signal just as for a black & white TV, and also transmitted the R and B in the extra colour signal. B&W TV's only saw Y, and colour TV's got Y, R and B. Since Y = R + B + G, G can be obtained as Y - (R+B), so they didn't need to transmit all three. To get both R and B into one signal, they use a combination of Phase and Amplitude modulation (think of it as AM and FM at the same time). Its called quadrature modulation, and works very well, but is susceptible to phase changes as it passes along cables, etc. If the signal gets +10 degrees phase change the colour will visibly change, which is why NTSC TV's have a tint control. PAL overcomes that by sending R and +B on one line, then R and -B on the next. That way a +10 phase shift on one line becomes -10 on the next, and small differences will cancel out. PAL TV's don't need tint controls. (Some old PAL sets may have a one, however). SECAM doesn't send both R & B together, it sends R on one line, B on the next. No fancy modulation, so no phase problems, but you need a 'memory' in the set to save up the signal from the previous line, since both R & B are required together for processing.
Mostly because of the different numbers of lines. Its quite easy to make one colour decoder which can cope with all the systems, but making a TV which can do 625 and 525 lines, 25 and 30 pictures/second, gets expensive. Consumers shop on price, no-one will buy a SECAM TV in the USA even if it only costs $20 more, since there aren't any SECAM channels.
Some can, but like TVs it costs more to make them adjust. The motor speed varies with the number of pictures transmitted per second, for example. (This is covered in more detail in the document: "Notes on the Diagnosis and Repair of Video Cassette Recorders".)
When originally developed, expense was considered based on contemporary technology. As noted, politics may have been equally important. As to which has better quality, its all rather subjective. The 625-line system adopted in Europe has better vertical resolution than the 525-line US system, but some people find the 50Hz field rate still produces some flicker. NTSC/PAL/SECAM are all equally capable of excellent colour reproduction, but under poor signal conditions NTSC can degrade more quickly.
Some others, like MAC where the colour and luminance are completely separated. That gets rid of interference (ever see the strange colours which appear on very fine check patterns?) but is more expensive and really only possible due to modern electronics.
That is THE question! There are certainly going to be different systems, more lines, better sound, etc.
Yes. If the PAL tape has 625 line pictures and the NTSC one has 525 line then you normally need a computer which can read in one format and re-adjust things. Not cheap, but becoming cheaper, several companies offer that sort of service. Some PAL VCRs can do a half-conversion, enough to fool most PAL TVs into thinking its got a PAL signal.
Sometimes. Some of it, depends a lot on the course and school.
(The following is from: Robert Rolf). SECAM: Used by France and the former Soviet union. No tint control. No color control. Full socialism. The state knows exactly what color you should see, and how strong that color should be. PAL: Used by Germany & UK, Australia etc. No tint control. A color control. Partial socialism. The state knows exactly what color you should see, but you get a choice as to how strong it can be. NTSC: Used in USA and Canada, Japan etc. A tint control, A color control. Uncontrolled socialism. The state lets you chose what color you see and how strong it can be. They then tax you regardless. Just another way of looking at it....
In the U.S., when PAL is mentioned, it is usually assumed to be 625 line/50 Hz as used in the UK and man other places. However, there are several variations on the PAL system. (The following from: Ed Ellers
31.5) What about PAL sets WITH a tint/hue control?Here is one for the record books - a Sony PAL TV that really wants to be NTSC! (From: Tony Duell (firstname.lastname@example.org)). Although this very old Sony set (KV1300) receives PAL signals, it's much closer to an NTSC set inside. In fact it's one of the strangest PAL decoders that I have ever seen. As you know, in the PAL system, the phase of one of the colour signals is inverted on each line, and in the receiver there's a bistable which switches at half the line rate to re-invert the colour signal on alternate lines. Well, to avoid a patent, the Sony set only uses (say) the in-phase colour signal that's received on alternate lines. For the lines in between it uses the previous line's colour signal (ignoring the incoming inverted one), which has been stored in a delay line. This approach avoids the main patent on the PAL system. It also means that this set doesn't automatically correct for phase errors in the colour signals - it's almost an NTSC decoder. Hence the hue control (which is also on my KV1320UB schematic). It's just about the only set like that.
31.6) TV, shortwave, power worldwide(From: Mark Zenier (email@example.com)). A book, "The World Radio TV Handbook" published by Billboard that covers TV, along with where all the world's shortwave radio transmitters are, and what sort of power comes out of the wall plug all around the world. It has a new edition each year and costs around $25 to $30.
31.7) Color television standards worldwide(The following is from EDMUNDO, Design Engineer Ten-Lab. This and additional information are available at: http://www.tenlab.com/format.htm). We at Ten-Lab have put together the following chart listing countries and their corresponding color TV standards. We are trying to be as accurate as possible, but we need your feedback to refine and correct the information. We are doing the best we can in spite of inherent problems such as: 1) Some of the literature and charts are contradictory; even some books and manuals contradict each other more than they agree. 2) Many countries have changed their names during the last few years. 3) Some countries have one broadcast TV system, but also receive programs in a different system from beyond their borders. This creates some confusion about the format(s) used locally. INTERNATIONAL TV STANDARDS CHART by TEN-LAB (UPDATED Jan 19, 1996) COUNTRY VHF STANDARD UHF STANDARD AFGANISTAN PAL/SECAM B ALBANIA PAL B PAL G ALGERIA PAL B PAL G ANGOLA PAL I ARGENTINA PAL N PAL N AUSTRALIA PAL B PAL G AUSTRIA PAL B PAL G AZORES PAL B BAHAMAS NTSC M BAHRAIN PAL B PAL G BANGLADESH PAL B BARBADOS NTSC M BELGIUM PAL B PAL H BERMUDA NTSC M BOLIVIA NTSC M BOTSWANA PAL I BOURKINA FASO SECAM K1 BRAZIL PAL M PAL M BRUNEI PAL B BULGARIA SECAM D SECAM K BURMA NTSC M BURUNDI SECAM K1 CAMBODIA NTSC M CAMEROON PAL B PAL G CANADA NTSC M NTSC M CANARY ISLANDS PAL B CHAD SECAM K1 CHILE NTSC M NTSC M CHINA PAL D COLOMBIA NTSC M NTSC M COSTA RICA NTSC M NTSC M CUBA NTSC M NTSC M CYPRUS PAL G PAL G CZECHOSLOVAKIA: now CZECH REPUBLIC PAL PAL SLOVAK REPUBLIC PAL PAL DAHOMEY SECAM K1 DENMARK PAL B PAL G DJIBHOUTI SECAM B SECAM G DOMINICAN REP NTSC M NTSC M ECUADOR NTSC M NTSC M EGYPT SECAM B SECAM G EL SALVADOR NTSC M NTSC M EQUATORIAL GUINEA PAL B ETHIOPIA PAL B PAL G FIJI PAL B FINLAND PAL B PAL G FRANCE SECAM L SECAM L FRENCH POLYNESIA K1 GABON SECAM K1 GAMBIA PAL I GERMANY PAL B PAL G GHANA PAL B PAL G GIBRALTAR PAL B PAL H GREECE SECAM/PAL B SECAM/PAL G GREENLAND NTSC M/PAL B GUADELOUPE SECAM K1 GUAM NTSC M GUATEMALA NTSC M NTSC M GUANA (FRENCH) SECAM K1 GUINEA PAL K HONDURAS NTSC M NTSC M HONG KONG PAL I HUNGARY SECAM D/PAL SECAM K/PAL ICELAND PAL B PAL G INDIA PAL B INDONESIA PAL B PAL G IRAN SECAM B SECAM G IRAQ SECAM B IRELAND PAL I PAL I ISRAEL PAL B PAL G ITALY PAL B PAL G IVORY COAST SECAM K1 JAMAICA NTSC M JAPAN NTSC M NTSC M JORDAN PAL B PAL G KENYA PAL B PAL G KOREA NORTH SECAM D KOREA SOUTH NTSC M NTSC M KUWAIT PAL B LEBANON SECAM B SECAM G LIBERIA PAL B PAL H LIBYA SECAM B SECAM G LUXEMBOURG PAL B PAL G/SECAM L MADAGASCAR SECAM K1 MADEIRA PAL B MALAGASY SECAM K1 MALAWI PAL B PAL G MALAYSIA PAL B MALI SECAM K1 MALTA PAL B PAL H MARTINIQUE SECAM K1 MAURITANIA SECAM B MAURITIUS SECAM B MEXICO NTSC M NTSC M MONACO SECAM L MONGOLIA SECAM D MOROCCO SECAM B MOZAMBIQUE PAL B NAMIBIA PAL I NEPAL PAL B NETHERLANDS PAL B PAL G NETH. ANTILLES NTSC M NTSC M NEW CALEDONIA SECAM K1 NEW GUINEA PAL B PAL G NEW ZEALAND PAL B PAL G NICARAGUA NTSC M NTSC M NIGER SECAM K1 NIGERIA PAL B PAL G NORWAY PAL B PAL G OMAN PAL B PAL G PAKISTAN PAL B PANAMA NTSC M NTSC M PARAGUAY PAL N PERU NTSC M NTSC M PHILIPPINES NTSC M NTSC M POLAND SECAM D/PAL SECAM K/PAL PORTUGAL PAL B PAL G PUERTO RICO NTSC M NTSC M QATAR PAL B REUNION SECAM K1 RUMANIA PAL D PAL K RUSSIA SECAM D SECAM K RWANDA SECAM K1 SABAH/SARAWAK PAL B ST. KITTS NTSC M NTSC M SAMOA NTSC M SAUDI ARABIA SECAM B/PAL B SECAM G SENEGAL SECAM K1 SEYCHELLES PAL B PAL G SIERRA LEONE PAL B PAL G SINGAPORE PAL B PAL G SOMALIA PAL B PAL G SOUTH AFRICA PAL I PAL I SPAIN PAL B PAL G SRI LANKA PAL B SUDAN PAL B PAL G SURINAM NTSC M NTSC M SWAZILAND PAL B PAL G SWEDEN PAL B PAL G SWITZERLAND PAL B PAL G SYRIA SECAM B TAHITI SECAM K1 TAIWAN NTSC M NTSC M TANZANIA PAL B PAL B THAILAND PAL B TOGO SECAM K TRINIDAD Y TOBAGO NTSC M NTSC M TUNISIA SECAM B TURKEY PAL B PAL G UGANDA PAL B PAL G UNITED ARAB EMIRATES PAL B PAL G UNITED KINGDOM PAL I UPPER VOLTA SECAM K1 URUGUAY PAL N PAL N USA NTSC M NTSC M VENEZUELA NTSC M NTSC M VIETNAM PAL B PAL G YEMEN PAL B YUGOSLAVIA PAL B PAL G ZAIRE SECAM K1 ZAMBIA PAL B PAL G ZIMBABWE PAL B PAL G
31.8) Cable channel allocation(The following is from: (firstname.lastname@example.org (Vincent Kruskal)). The following table gives the definitions of the numeric cable channels defined in the EIA (Electronic Industries Association) Interim Standards, IS-6 (CP), May 1983 and associated information that has been gathered. Definitions appear at the end. HRC Picture Channel Carrier Cable Band Other Names -------- ------- ----------- -------------------------- 1 72 MHz Low (VAR) A-8, C54, J54, G64, 4+, 5A 2 54 Low 3 60 Low 4 66 Low 5 78 Low A-7, C55, J55, G65 6 84 Low A-6, C56, J56, G66 7 174 High 8 180 High 9 186 High 10 192 High 11 198 High 12 204 High 13 210 High 14 120 Mid A 15 126 Mid (ATC) B 16 132 Mid (ATC) C 17 138 Mid (VAR) D 18 144 Mid (VAR) E 19 150 Mid (VAR) F 20 156 Mid (VAR) G 21 162 Mid (VAR) H 22 168 Mid (VAR) I 23 216 Super (VAR) J 24 222 Super (VAR) K 25 228 Super L 26 234 Super M 27 240 Super N 28 246 Super O 29 252 Super P 30 258 Super Q 31 264 Super R 32 270 Super S 33 276 Super T 34 282 Super U 35 288 Super V 36 294 Super W 37 300 Hyper AA, W+1 38 306 Hyper BB, W+2 39 312 Hyper CC, W+3 40 318 Hyper DD, W+4 41 324 Hyper EE, W+5 42 330 Hyper FF, W+6 43 336 Hyper GG, W+7 44 342 Hyper HH, W+8 45 348 Hyper II, W+9 46 354 Hyper JJ, W+10 47 360 Hyper KK, W+11 48 366 Hyper LL, W+12 49 372 Hyper MM, W+13 50 378 Hyper NN, W+14 51 384 Hyper OO, W+15 52 390 Hyper PP, W+16 53 396 Hyper QQ, W+17 54 402 Hyper RR, W+18, C62 55 408 Hyper SS, W+19, C63 56 414 Hyper TT, W+20, C64 57 420 Hyper (HAM) UU, W+21, C65 58 426 Hyper (HAM) VV, W+22, C66 59 432 Hyper (HAM) WW, W+23, C67 60 438 Hyper (HAM) AAA, W+24, C68 61 444 Hyper (HAM) BBB, W+25, C69 62 450 Hyper (HAM) CCC, W+26, C70 63 456 Hyper DDD, W+27, C71 64 462 Hyper EEE, W+28 65 468 Ultra U14, FFF, W+29 66 474 Ultra U15, GGG, W+30 67 480 Ultra U16, HHH, W+31 68 486 Ultra U17, III, W+32 69 492 Ultra U18, JJJ, W+33 70 498 Ultra U19, KKK, W+34 71 504 Ultra U20, LLL, W+35 72 510 Ultra U21, MMM, W+36 73 516 Ultra U22, NNN, W+37 74 522 Ultra U23, OOO, W+38 75 528 Ultra U24, PPP, W+39 76 534 Ultra U25, QQQ, W+40 77 540 Ultra U26, RRR, W+41 78 546 Ultra U27, SSS, W+42 79 552 Ultra U28, TTT, W+43 80 558 Ultra U29, UUU, W+44 81 564 Ultra U30, VVV, W+45 82 570 Ultra U31, WWW, W+46 83 576 Ultra U32, AAAA, W+47 84 582 Ultra U33, BBBB, W+48 85 588 Ultra U34, CCCC, W+49 86 594 Ultra U35, DDDD, W+50 87 600 Ultra U36, EEEE, W+51 88 606 Ultra (RA) U37, FFFF, W+52 89 612 Ultra U38, GGGG, W+53 90 618 Ultra U39, HHHH, W+54 91 624 Ultra U40, IIII, W+55 92 630 Ultra U41, JJJJ, W+56 93 636 Ultra U42, KKKK, W+57 94 642 Ultra U43, LLLL, W+58 95 90 Low (FM) A-5, C57, J57 96 96 Low (FM) A-4, C58, J58 97 102 Low (FM) A-3, C59, J59 98 108 Low A-2, C60, J60, G60 99 114 Low A-1, C61, J61, G61 100 648 Ultra U44, MMMM, W+59 101 654 Ultra U45, NNNN, W+60 102 660 Ultra U46, OOOO, W+61 103 666 Ultra U47, PPPP, W+62 104 672 Ultra U48, QQQQ, W+63 105 678 Ultra U49, RRRR, W+64 106 684 Ultra U50, SSSS, W+65 107 690 Ultra U51, TTTT, W+66 108 696 Ultra U52, UUUU, W+67 109 702 Ultra U53, VVVV, W+68 110 708 Ultra U54, WWWW, W+69 111 714 Ultra U55, AAAAA, W+70 112 720 Ultra U56, BBBBB, W+71 113 726 Ultra U57, CCCCC, W+72 114 732 Ultra U58, DDDDD, W+73 115 738 Ultra U59, EEEEE, W+74 116 744 Ultra U60, FFFFF, W+75 117 750 Ultra U61, GGGGG, W+76 118 756 Ultra U62, HHHHH, W+77 119 762 Ultra U63, IIIII, W+78 120 768 Ultra U64, JJJJJ, W+79 121 774 Ultra U65, KKKKK, W+80 122 780 Ultra U66, LLLLL, W+81 123 786 Ultra U67, MMMMM, W+82 124 792 Ultra U68, NNNNN, W+83 125 798 Ultra U69, OOOOO, W+84
31.9) Notes on cable and broadcast frequencies(The following is from: (email@example.com (Vincent Kruskal)). RF band: To get the band, subtract 1.25 from picture carrier (low end) and add 4.75 (high end). Color subcarrier: Add 3.58... to picture carrier. Sound carrier: Add 4.5 to picture carrier. HRC: Harmonically Related Carrier. Makes both second- and third-order beats invisible by making them fall directly on the picture carrier of other channels. That is, multiplying the picture carrier by two or three will yield exactly another picture carrier. IRC: Incrementally Related Carrier, add 1.25 to HRC frequency. A General Instruments (Jerrold) catalog said that IRC makes third-order (more important than second-order) beats invisible by making them fall directly on the picture carrier of other channels. But it is not true that multiplying an IRC picture carrier by two or three yields another IRC picture carrier. This contradiction has not been resolved. The reason third-order harmonics are more important is that oscillators and amplifiers tend to generate odd-order harmonics far more than even-order ones. Broadcast frequency: Add 1.25 to HRC frequency except for channels 5 and 6. For them, subtract 0.75. But these are just nominal frequencies. The FCC actually has three channel designations for each number as in 5, 5- and 5+. The minus channels are 10 kHz below the nominal value and the plus channels are 10 kHz above. For example:
31.10) How did the (vertical) frame rate get chosenSome people think that TVs are synchronized to the local power line since the vertical scan rate is around 60 Hz (or 50 Hz). This is not correct. No TV (at least once the broadcast standards were defined - some experimental schemes did) ever used the power line for synchronization. However, older TVs had line frequency power transformers (no SMPSs) whose stray magnetic fields could affect the CRT deflection slightly. So it made sense (well, this is one justification at least) to make the vertical scan rate (field rate) equal to the power line frequency. Otherwise, there would be a jiggle or wiggle in the picture due to the stray magnetic field affecting the deflection of the beam inside the CRT. Since it was thought at the time (and for other reasons as well like cost) that 60 Hz was adequate to produce an acceptable amount of flicker, this all fit together nicely. In the good old days before color TV, the frame/field rate was exactly 30/60 Hz (or 25/50) Hz. With color, it had to be changed slightly (see the section: "Why is the NTSC color subcarrier such a weird frequency?") but since TVs no longer use line power transformers, there would not even be a slow position shift (period of several seconds) due to this so it didn't matter.
31.11) Why is the NTSC color subcarrier such a weird frequency?(The following is from Bob Myers (firstname.lastname@example.org)). Actually, if we wanted to define the rates to the Nth degree, the important starting point is the field rate. The NTSC color frame rate was defined as (60 * 1000/1001) Hz, which is a bit more than 59.94 Hz. From this rate, all the others in the system are defined. The line rate is 262.5 times this, and the color subcarrier is defined as 455/2 times the line rate. This is often given as simply 3.579545 MHz, but the the color subcarrier was actually derived from the line/field rates rather than the other way around. The whole thing was done so as to avoid (or at least minimize) interaction between the luminance, chrominance, and audio subcomponents in the standard color signal. This could have been achieved by moving either the audio subcarrier or adjusting the line and frame rates as described above. Unfortunately, the latter route was chosen, leaving us with this very strange looking set of rates. The precise color burst frequency winds up being 3.579545.4545... under this definition, but giving it to the nearest Hz is within the tolerances of the system.
31.12) What is the maximal allowed deviation of the horizontal frequency?(The following is from: Peter Bennett VE7CEI (email@example.com)) In Canada and the US (525 line, 60 HZ, NTSC), the horizontal frequency is 15,734.264 Hz. The colour subcarrier is 455/2 times the horizontal frequency which should come to 3.579545 MHz. I believe the tolerance on the subcarrier frequency is +/- 10 Hz.
31.13) Informal comparison of TV standardsQ: I heard that TV in certain part of Europe has more quality in Europe then here in North America. I'd like to know the differences between the two systems. Is that why we cant use video tapes from there? (Responses from: Mark Zenier (firstname.lastname@example.org or email@example.com)) The first difference is that a lot of the world runs on 50 Hz power as opposed to North America's 60 Hz power. In the olden days, before active power supply regulators got cheap, it was decided that the vertical scan rate match the power supply frequency, so that ripple in the power supply wouldn't produce obnoxious visual effects. So the PAL/SECAM signals have 50 vertical scans per second. I don't know the exact reasoning, but the horizontal scan rate is close to the same. 15750 (now 15734) for 60 Hz, and 15625 for 50 Hz systems. My guess is the tradeoff between cost (50 years or so ago) and audibility for a large portion of the population. So 50 Hz systems have more lines - 625 vs. 525 lines for 60 Hz systems. The second difference is that European TV channels are wider. 7 or 8 MHz compared to the North American 6 MHz. Video bandwidth is limited to 4.2 MHz in a 6 MHz channel, but can be as much as 6 MHz in some of the 50 Hz systems. (Note: Systems is plural. There are many different European systems with incompatible color and sound transmission methods.) As for the quality, if you move a little farther away, so that a pixel on each system subtends the same angle, NTSC doesn't have a poorer picture, just a smaller one.
31.14) PAL-plus"I wonder if you could tell me about PAL-Plus. The last time I was in Germany was in '84 so I've been out of touch with them." (From: Jeroen H. Stessen (Jeroen.Stessen@ehv.ce.philips.com)). Oh boy, here goes another long story: PAL-plus is an attempt to extend the life-cycle of terrestrial PAL transmissions by including compatible wide-screen (16:9) transmissions. It is an advanced variant of the letterbox format, this means that when you receive a PAL-plus widescreen program on an older 4:3 receiver you will see black bars top and bottom. It was originally developed in Germany (university of Dortmund in cooperation with German terrestrial broadcasters and some setmakers). Later a large consortium of European and Japanese setmakers took over and finished the job. Strangely, the German broadcasters seem to use PAL-plus only very rarely. The PAL-plus standard comprises three extensions to the PAL-standard: 1. Vertical helper. In order to compensate for the fact that 1/4 of the video lines are not used, which would deteriorate vertical resolution for the widescreen viewer, the missing vertical information has been coded into the black lines in a manner as to be nearly invisible on a 4:3 receiver (you see some dark blue). The 16:9 PAL-plus receiver combines 432 visible lines plus 144 helper lines into 576 new visible lines. 2. Colour-plus. The PAL colour carrier is modulated in a slightly different way (making use of correlation between 2 fields) in order to give a cleaner Y/C separation in the PAL-plus receiver. 3. Signaling bits from which the receiver can conclude whether the transmission is 4:3/16:9/PAL-plus and adapt the display format accordingly. The bandwidth of these bits is low enough to survive recording on a VHS recorder. In order to enable a poor-man's PAL-plus receiver, the standard permits using the mark "PAL-plus" if at least the vertical helper reconstruction is included. Colour-plus is optional, so you will find sets on the market with only half of the PAL-plus extension. PAL-plus may also be combined with teletext, ghost cancellation reference, digital Nicam stereo, VPS, PDC and what-you-have more. Theoretically it can be broadcast over a satellite channel too, but it was not designed for that and some aspects of a satellite channel do indeed give interesting technical problems. There are also sets marketed as "PAL-plus compatible". These are mostly widescreen sets without any PAL-plus processing at all, but they allow switching of the display format between 4:3 and 16:9. They may well do that automatically, based on the signaling bits. There are 2 methods for displaying a 4:3 letterboxed signal on a 16:9 display, without using the PAL-plus helper lines: 1. Increase of the vertical deflection amplitude to display only the centre 432 lines. 2. Vertical interpolation without using the helper, to convert 432 lines into 576 lines and display on a 576 lines display. Both modes may be called "movie expand". Only when you really convert to full-resolution widescreen will it be called "widescreen". And there are 4 methods for displaying a regular 4:3 signal on a 16:9 display (regular PAL, has nothing to do with PAL-plus): 1. Decrease of the horizontal deflection amplitude, this gives black bars left and right. 2. Horizontal interpolation, to convert N pixels to 3/4*N pixels. Both modes may be called "4:3" or "normal". 3. Non-linear horizontal deflection waveform, called "Panorama mode" by JVC, works by increasing the S-capacitor value. 4. Non-linear horizontal interpolation, called "Superwide" by Philips, works with an advanced sample-rate converter. With both modes, the left and right edges of the picture will be stretched to fill the left and right bars, but the aspect ratio of the centre part of the picture will hardly be affected. Interesting, huh?Go to [Next] segment
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