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mpressive but not yet perfect During November 1989, both the Japanese and European systems of high definition television (HDTV) were displayed in Sydney, coinciding with a conference hosted by the Australian Broadcasting Tribunal entitled "Television 2000: Choices & Challenges". By LEO SIMPSON The Japanese were first into the HDTV arena and had prototype systems on display as long as 10 years ago. Their system is 1125 lines at a field rate of 60Hz - many people would have seen it at Brisbane during Expo 88. But in the last three years or so, the Europeans have put in an enormous effort and have now produced a full line of HDTV equipment from cameras and recorders to large screen CRT and rear projection TV sets, all in the new wide format. The European HDTV standard is 1250 lines and 50Hz - much closer in compatibility to our present PAL system of 625 lines and 50Hz. Considering that the Europeans have had to go from a standing start, they have made a prodigious effort. Unfortunately, it was not possible to make side-by-side comparisons between the Japanese and European systems since they were on display at different venues - the Japanese at the Hilton International Hotel and the European system at the Sydney Opera House. And as it happened, we saw the two systems on different days in the same week. 10 SILICON CHIP In spite of this, we can report on the similarities and differences between the systems and though you might not expect it, they are considerable. In fact, when you come right down to it, the two HDTV systems are exactly the same in only one respect - the new wide aspect ratio screens. These wide screens used to be referred to as having an aspect ratio of 5:3.33 (as opposed to the 4:3 aspect of conventional TV screens). HDTV wide scr.e en format is now referred to as 16:9 which is somewhat easier to say and think about. Either way, the wide screen format is the same as used in cinema theatres. Fine line structure When you look at a large conventional TV screen from a distance of one metre or so, you are conscious of the horizontal scanning lines and of the vertical dot structure. In HDTV screens of much the same size and at the same viewing distance, the line structure is no longer apparent - you have to look closely to see it. The picture tubes also have a much finer pitch. So these two factors are the main differences between HDTV and current PAL TV as we know it. The wide format screen is more attractive than the current format but this in itself is not enough to make you long to see HDTV introduced. TV sets using the wide screens are extremely bulky by the standards we have become used to. For example, a 16:9 aspect TV with a screen 60cm wide will have a cabinet which is very deep at around 60cm or so. Some of the current widescreen sets using picture tubes would be difficult to get through the doors in many homes. This is because the widescreen HDTV tubes are using 90° deflection yokes rather than the 117 ° of current TV picture tubes. At least, we assume that the tubes are 90° deflection, to obtain better convergence. There is no other reason to explain the great depth of the sets. This is a factor which would probably make most people decide against a HDTV set in their home. They are far too bulky. Wide projection screens Ah, but what about HDTV rear projection sets? The Japanese and Europeans had 50-inch (127cm) rear projection HDTV sets on display and these are truly impressive. It is these sets that most people were drawn to. While not quite as bright or as sharp as the picture tube sets, their very size is the attraction. And they are nowhere near as deep as the sets with picture tubes. •◄ ,, "..- . h ,:: . , -: , In Europe, they are getting ready for D2-MAC broadcasts via satellite . The Europeans see D2-MAC as the first step along the road to high definition TV. Our reaction was that when HDTV is introduced into Australia (and we have no doubt that it ultimately will be), most sales will be of the really large rear projection sets. As far as we are concerned, if you are going to go for HDTV, you may as well go the whole hog. The day of the "theatre in your home" will be at hand. However, it was the large screens which brought to light a disadvantage of the European HDTV system - flicker. Because their screens are so much wider you have a much wider field of view and therefore more visual information coming into the corners of your eyes. And so you are more sensitive to flicker. By contrast, the Japanese system, operating at 60Hz, has no flicker at all. If the European system is to succeed, it will have to increase the field rate, by means of a field store in the receiver, to 100Hz. 100Hz sets based on the DZ-MAC system were also on display during November, 1989. Paradoxically, the HDTV system displayed by the Japanese did not appear to have enough "high definition". Actually, the Japanese had two HDTV exhibits. One, using a 120-inch screen, was using the full 30MHz bandwidth video and was truly spectacular - as good as, if Philips showed this impressive 50-inch rear projection HDTV set during the Eureka demonstrations in Sydney. HDTV sets use screens with a 16:9 aspect ratio as opposed to the 4:3 aspect ratio of conventional sets. not better, than 35mm film. The second HDTV display, which had one 50-inch rear projection screen and a variety of wide format picture tube sets, was using video signals processed by MUSE (MUltiple Sub-nyquist Sampling Encoding). This is a complex video encoding bandwidth compression system which gets the necessary signal bandwidth down to 8.1MHz to make it suitable for satellite transmission. Bandwidth reduction One of the tricks used by the MUSE system is to reduce the video bandwidth more for moving picture information than for stationary pictures. Maximum reproducible luminance bandwith for stationary pictures is 22MHz while chrominance bandwidth is 14MHz. By contrast, effective luminance bandwidth for moving picture information is 14MHz and the chrominance bandwidth is even less, at just 3.5MHz. The reduction in bandwidth for moving picture information is justified by the MUSE system inventors, NHK Science and Technical JANUARY 1990 11 The Japanese also showed a 50-inch.:rear projecti?n set at t_heir Sydney demonstration. Large screen size will be the mam attraction of HDTV. Research Laboratories, on the basis that the human eye is more tolerant of image blurring when objects are moving. Be that as it may, our impressions of the MUSE images, displayed on both rear projection sets and wide format picture tube sets, were that there was just not enough bandwidth. All the pictures were via tape and there was a general lack of really finely focussed, bright and sharp images. On the few closeups of faces that were seen there was none of the sharpness that can be seen from first class PAL TV images - individual hair strands, wrinkles, skin pores and so on. Why weren't these present? We have to assume lack of sufficient bandwidth. Europeans came from two sources. The first was direct video from a camera aimed at Sydney's Circular Quay. The images were bright and very sharp - no apparent lack of bandwidth here, even though a similar degree of bandwidth compression is employed. There was also a variety of taped video including scenes from the French Bicentennial. While the latter could only be summed up as tedious television, the images were bright and sharp, even on the rear projection sets. The footage from the French Bicentennial also included some night scenes which demonstrated that the new HDTV Plumbicon camera tubes have quite good lowlight sensitivity. The European experience Eureka is the name given to a cooperative venture backed by European governments and by ma- On the other hand, the HDTV picture information displayed by the Eureka and HDMAC Developed by Philips, this S-VHS video recorder features a built-in D2-MAC decoder and can also be linked to a Eurocrypt pay TV card reader. 12 SILICON CHIP jor companies such as ThomsonCSF (France), Bosch (Germany), Philips (Netherlands) and some 30 odd others. Over 600 engineers are working on every aspect of HDTV - from cameras to recorders and receivers. The system will embrace satellite and cable TV systems and has encryption for pay TV systems. It also has large data transmission capability and up to eight sound channels. The basis of the new European TV standard is DZ-MAC which is similar to but not compatible with the B-MAC system used by Aussat and the ABC for outback TV services via satellite. MAC stands for Multiplexed Analog Components and is a time division system which transmits the sound, luminance and chrominance information in a sequence for each line rather than frequency multiplexed together as in the PAL and NTSC systems. B-MAC and DZ-MAC are said to give 50% more picture bandwidth than PAL and indeed they give a brighter, sharper picture. HDMAC is the HDTV version of DZ-MAC and the Europeans are heavily plugging it since it is compatible with DZ-MAC which, in turn, is said to be more readily compatible with the existing PAL system (via decoders) than the Japanese HDTV system. HDMAC also involves substantial bandwidth compression to make it compatible with DZ-MAC but the ultimate picture quality appears to be better than Japanese HDTV pictures processed via MUSE. One point is clear. The Europeans have come far enough in three years to make sure that the Japanese will no longer have all the running in HDTV, at least not in countries which presently have thePAL system. In fact, it is clear that the Japanese are going to be shut right out of Europe with HDTV. As far as Australia is concerned, we will probably get HDTV via a cable pay-TV system and that will possibly be in the late 90s. What system will we use? Who knows but no decisions should be made by the government at this early stage. As far as we were concerned, after seeing both versions, HDTV is good but NYP - "not yet perfect". ~