Tema: 10 Mitos sobre la HDTV.

PC World Describes 10 HDTV Myths

The world of high-definition television can be as confusing as it is alluring

By Yardena Arar From the December 2005 issue of PC World magazine

Plasma TV sets start out bright and beautiful, but burn out to an early death. Every single high-definition television program looks equally crisp and gorgeous. The higher resolution of a 1080p high-def set means that your shows and DVDs will always look better than on a more ordinary 720p set. Are these gospel truths about HDTV? Nope. Just a sampling of the many popular factoids, half-truths, and myths that can make choosing and enjoying a high-def television set complicated and confusing--and in some cases, needlessly expensive.

To help dispel these myths, we consulted an A-team of HDTV experts. The challenge: Identify and debunk troublesome, costly, and all-too-prevalent misconceptions about high-definition TV--from the basics of broadcasting to the arcane secrets of hardware. We lay out the facts you'll need to have at your disposal in order to make the right decisions. Armed with this information, you'll know just what to expect when you take the HDTV plunge.

1.- "An HD set is all you need to get high-def programs."

In our dreams! To experience the vibrant images and the Dolby 5.1 sound of true high-definition TV, you need several things--and an HD-ready set (a display that can accept HD-format input and display it at a minimum of 720 lines of progressive-scan or noninterlaced video) is just one of them.

First, a show needs to be shot in high definition, and that may not be the case, even when a show claims that it is. Bjorn Dybdahl, owner of Bjorn's, a high-end audio-video store in San Antonio, Texas, says that he's seen many high-def sports broadcasts shown partly in standard definition because the producer is using some non-HD cameras in its coverage. And although TNT's digital channel presents Law & Order reruns in high definition, early episodes weren't shot in HD; as a result, in those episodes, you see a 4:3 standard-def show that is stretched and scaled up to high-def size. It doesn't look great.

Second, the program must be transmitted in high def by a station that you can receive either over the air or from your cable or satellite provider. ("Shown in high definition where available" doesn't mean it's available to you.)

Third, you need an HD receiver to process the signal. A set that has a built-in ATSC digital tuner can display over-the-air HD broadcasts with nothing more than a good antenna. ATSC, which stands for Advanced Television Standards Committee, is the group that defined the 18 formats of the coming digital TV system, only 6 of which are considered high definition. (And by the way, there is no such thing as an HD antenna--there are just antennas.) If your HDTV set comes with picture-in-picture, you won't get high-def-picture-in-high-def-picture unless your set comes with two ATSC tuners.

An HD-ready set lacks such a tuner, so you'll need either a set-top box with a tuner, or an HD box from your cable or satellite service. Regardless of the box you get, you need to make sure that you're feeding its digital output into your HD-ready set. "A lot of people will get an HD-ready set [and] an HD cable box, but they will use the analog feed from the HD box," says Jeff Cove, Panasonic's vice president for technology and alliances.

Finally, you must tune your HDTV set to a high-definition channel showing actual HD content. Picking up the analog transmission from your local affiliate on your high-def cable box won't result in delivery of a show in HD.

2.- "The bigger your HDTV set, the better it will look."

Bigger isn't better if you are seated so close to the set that you can see every pixel or line of resolution. Generally, you don't want to sit closer to a 720p HDTV than twice the length of the screen diagonal.

On the other hand, if you sit too far away from a high-resolution TV, its special benefits may disappear. "For an awful lot of viewing, what limits the resolution is the human eye," says Larry Web-er, president-elect of the Society for Information Display, a group of display industry pros. At a distance of 10 feet from the screen, the eye can't detect pixels smaller than 1 millimeter; so if you look at a 37-inch set from that far away, you won't notice significant difference between a high-definition image and a standard-def image.

Content also affects perceived image quality. Digital TVs are fixed-pixel displays--the screen resolution is hard-wired, so content has to be scaled, or adjusted, to fit the screen resolution. Not surprisingly, most television content is most attractive when displayed at its native resolution. That's why today's DVD movies, which reproduce the original film at 480 lines of progressive-scan video, may look better on an Enhanced Definition TV than on an HDTV: EDTV has the same screen resolution (480p) that DVDs have, while HDTV must scale the number of lines to 720p or 1080p (depending on the set), usually via software interpolation.

Conversely, to display HD programming, an EDTV has to eliminate lines of content (once again, usually by software interpolation), and on larger sets the resulting quality loss may be quite obvious.

3.- "The higher the screen resolution, the better the image quality of an HDTV."

Most HDTV sets today are 720p displays, but a few vendors are beginning to offer 1080p sets--either LCDs or rear-projection micro-display (LCD, LCoS, DLP) models. As yet, no 1080p plasmas are available (though some have been announced in very large sizes). These sets will clearly do the best job of handling 1080p content--when it arrives. But today's HDTV shows are shown in either 720p or 1080i format: nobody broadcasts in 1080p because of bandwidth issues. Movies may someday be available in 1080p on optical media, but Hollywood hasn't settled on the next-generation hardware standard (Blu-ray or HD-DVD), much less chosen a content format.

Lack of 1080p content is one reason some vendors are holding off on introducing 1080p sets. But those that are selling 1080p sets point out that some HDTV is broadcast in 1080i, and that such content arguably looks better on a 1080p set because less scaling is involved. (On the other hand, 720p content has to be scaled up for a 1080p set.) Here again, though, the capabilities of the human eye come into play: You'll probably notice the superior resolution of 1080p only if you sit very close to the set--or have an extremely large set.

4.- "You have to relinquish the fluid motion of a CRT screen when you move up to HDTV."

Not at all. You can purchase a high-definition CRT set--and you'll save a lot of money if you do, because they cost less than LCD and plasma-screen televisions of similar size. But in doing so you'll lose the sleek flat-panel chic of a plasma or LCD set. If you want that slim profile, however, be aware that LCDs have trouble rendering fluid motion, as a result of their somewhat pedestrian response times. Plasma and DLP screens aren't susceptible to this technological weakness.

5.- "Burn-in will wreck your plasma HDTV within a year."

The plasma display has advanced since the days when most of us saw plasmas only at airports, where constantly switched-on screens showing formatted flight information suffered from burn-in--ghost images that linger on screen despite no longer being transmitted.

Today, vendors rate the life expectancy of high-quality plasma TVs at 60,000 hours. That works out to more than 20 years of use if you watch 8 hours a day, 365 days a year; it's also about the same lifetime claimed for LCDs and CRTs (the latter are similarly prone to burn-in because, like plasma TVs, they depend on phosphor-based displays).

What changed? Phosphors and gas mixtures in the new plasma panels greatly reduce the risk of burn-in, and some sets use burn-in prevention software. "If you're not worried about burn-in for your CRT, you shouldn't worry about it for your plasma TV," says the Society for Information Display's Larry Weber.

6.- "Bright LCDs look beautiful everywhere, and they use much less power than plasma or CRT sets do."

It's true that LCDs are bright, which makes them a good choice if you watch TV in a brightly lit room. But if you're inclined to turn down the lights for your rendezvous with Entourage or Medium, you probably don't want the brightest set on the block, and plasmas and CRTs offer superior color capabilities without introducing the response-time (and associated motion artifacting) issues that have long plagued LCDs.

As for power consumption, a study by Japan's Green Purchasing Network--an organization dedicated to promoting environmentally friendly purchasing by consumers, business, and government--concluded that the power consumption of similar-size plasma, CRT, and traditional LCD displays in real-world viewing situations is practically the same. However, the coming generation of LCDs that use LED backlighting, while expected to deliver significantly better color, will consume roughly twice as much power as traditional LCDs of the same size.

7.- "These pricey TVs look so great out of the box that it's a waste to pay a small fortune to have a professional calibrate your set."

That's a double-whammy myth. It's well known in the TV business that vendors usually ship sets turned to their highest possible brightness level, since brightness draws customers on the showroom floor. At home, however, many people watch TV under low lighting conditions in which an overly bright set can look jarring. In addition, the TV may arrive with less-than-accurate color settings. Consequently, almost any set will benefit from calibration. A professional calibrator has tools that can access settings most of us can't reach--and shouldn't, since we wouldn't know what to do with them. But the pros do charge a few hundred dollars for their services, and you can achieve reasonably good results on your own with software such as the $40 DVD Essentials.

8.- "All true HDTV programming looks equally great."

This claim gets us to a dirty little secret of HD broadcasting: All HDTV programs are compressed--some to a greater extent than others.

The FCC allots each TV station sufficient airwave spectrum to broadcast a little over 19 megabits per second of data, but stations aren't required to devote their share to a single high-def program. They may compress an HD show enough to leave room for one or two standard-def broadcasts as well--a practice known as multicasting.

The ATSC standard includes support for MPEG2 video encoding, but it says nothing about compression levels. Broadcasting an uncompressed MPEG2 video would require 885 mbps (for 720p content) or 995 mbps (for 1080i content). A station that broadcasts a single HD program can devote only 18 mbps to it, HDTV consultant Peter Putman says; and to get that, broadcasters have to use a compression ratio of 49:1 for 720p and 55:1 for 1080i.

If a station uses its bandwidth to broadcast both an HD show and a standard-def show, the HD program has to fit into 13 or 14 mbps. And a station sending out two standard-definition channels along with an HD channel must compress the HD signal to roughly 13.5 mbps, which entails compression ratios in the vicinity of 66:1. Such high compression produces artifacts that might not be noticeable on a small CRT, but can be quite obvious on a big fixed-pixel display. These include mosquito noise, an effect in which small dots seem to surround a person's head; and macroblock errors, similar to what a fast-moving video game looks like on a PC with too little graphics power.

You can get a hint of how much a station compresses its video by learning whether it multicasts. But generally speaking, satellite and cable carriers compress HD programs more than over-the-air broadcasters do. Though they have a lot more bandwidth at their disposal than terrestrial stations, these pay-TV carriers need it for sending out the dozens of channels their subscribers expect (not to mention extras like Internet access). Dish Network has said that, because of bandwidth constraints, it will gradually move all of its customers to equipment that supports MPEG4 encoding, which is more efficient than MPEG2. But sometimes it's out of the carriers' hands, too. Pay-TV content providers such as Discovery, ESPN, and HBO also compress their programs before beaming them to the cable and satellite services.

9.- "Standard-definition TV is unwatchable on HDTV."

Well...this is a case of hyperbole, not of outright fabrication. True, standard-def programming will never look as good as HD programming on an HDTV because of the scaling issues mentioned previously. But vendors are toiling to better the SD experience on their HD sets, and the success of these efforts varies between vendors and sets. So if you're expecting to watch standard-definition TV on an HD set, make sure that you do your own taste tests.

10.- "I'll have to toss all my current analog sets when the digital conversion kicks in."

Though this is not strictly an HDTV issue, it is a common misconception about the digital transition, which Congress seems bent on completing by 2008. At that point your old sets won't be able to snag over-the-air broadcasts without help, but you should still be able to use them by buying inexpensive digital-to-analog converters. And cable or satellite boxes will still work because the service provider will take care of the conversion. Of course, you won't be able to experience HDTV on an analog set.

These may not be the only myths you'll encounter in your quest for the perfect HDTV--and you can't trust everything you hear (or see) in a showroom. So careful research is essential before you pay for what's likely to be the most expensive TV set you've ever bought. And that is the gospel truth.

http://www.pcworld.com/reviews/artic...,122629,00.asp

Por cierto habeis visto el mito numero 5... )

5.- "Burn-in will wreck your plasma HDTV within a year."

The plasma display has advanced since the days when most of us saw plasmas only at airports, where constantly switched-on screens showing formatted flight information suffered from burn-in--ghost images that linger on screen despite no longer being transmitted.

Today, vendors rate the life expectancy of high-quality plasma TVs at 60,000 hours. That works out to more than 20 years of use if you watch 8 hours a day, 365 days a year; it's also about the same lifetime claimed for LCDs and CRTs (the latter are similarly prone to burn-in because, like plasma TVs, they depend on phosphor-based displays).

What changed? Phosphors and gas mixtures in the new plasma panels greatly reduce the risk of burn-in, and some sets use burn-in prevention software. "If you're not worried about burn-in for your CRT, you shouldn't worry about it for your plasma TV," says the Society for Information Display's Larry Weber.

Comenta que la vida de los plasmas en este momento llegan a las 60.000 horas. :8))

Y continua diciendo que las ultimas generaciones de plasmas evitan el quemado gracias a la mezcla del fosforo y gas asi como el uso de un software que previene tambien dicho efecto.

Y continua diciendo que las ultimas generaciones de plasmas evitan el quemado gracias a la mezcla del fosforo y gas asi como el uso de un software que previene tambien dicho efecto.

Toshiba modelo año 2004-5, quemada con fondo del Bloomberg (9 meses de uso y las 18 horas encendidas cada día, includio sabados y Domingos).
La franja que separa el Ticker de la información del locutor en pantalla queda claramente marcada.
Así que.... que sigan vendiendo la moto a otro.