TV or Not TV: Ax HDTV Technology Primer

I've been looking at HDTVs lately, and it's one of those technologies that's kind of confusing when you get started - there are so many acronyms and new terminology - your eyes tend to glaze over when trying to figure out what it all means. So here is a little primer for you, since I bit the bullet and did the research!

First, we tend to stick all large TVs into the general grouping, "big screen tv."

But there are some essential differences among the many models. And you also need to understand that many people are now watching "TV" via a monitor connected to a cable, or running their monitor off a television-receiver-equipped computer (using something like Hauppage's WinTV).Technically, "TV" implies the presence of a receiver. A receiver is simply that portion of a television that picks up and interprets the television signal that's being pumped out into the "air" by a television station. If you have a cable box, it replaces that function - the cable box accepts the data being streamed over the cable and allows you to choose which "channel" you want to watch. If you have a cable but no box (basically, a legacy "drop" from the cable company), you will still need a receiver in the television set in order to see anything; these are the so-called "cable-ready" TVs of yesteryear.

In the Big Screen designation, there are three basic types of technology: LCD, Plasma, and Projection. And there are two types of Projection TV, front and rear.

Projection TVs are more or less "old" technology. They were among the first big screen televisions, and while the picture can be just fine, they tend to require so much in terms of setup (there has to be a proper wall and space enough for the projector to work from behind, or clear space in front for the projector to be able to do its thing), that they aren't very popular any more - except that they are significantly cheaper, and you can get a  much larger screen for a much lower price than for a comparable LCD or Plasma TV.

LCD and Plasma both offer the advantages of a slimmer profile (and if you really want to go thin, you'll want to look at recently-released OLED models - organic light-emitting diodes, which can permit a flat panel TV that's less than an inch thick!) and superior picture quality, as compared to the cathode-ray tube TVs from the old days. Cathode-rays tubes are necessarily bulky, and are limited to about a 40-inch display by virtue of the tube technology itself. So when manufacturers wanted to go bigger, they had to figure out a new way to make a television.

LCD (liquid crystal display) TVs use two glass plates with liquid crystals between them, and to put it in simplest terms, light passes through the crystals, causing them to behave in ways that result in a picture to your eye. A Plasma TV is similar in that it's made up of two glass plates, but this time with gas-filled cells sandwiched between them, which, when charged, will react by creating what we perceive as a picture. Both, just because of the way they're made, result in a much smaller profile than their predecessors.

Another designation you'll need to know is "p" versus "i."

"P" simply refers to "pixels," and is a way of telling you the theoretical upper limit of the number of pixels a television is capable of displaying. So when you see "1080p," it means that, ideally, this television will be able to display 1920x1080 pixels - which is what is required for HD viewing from, say, a full HD broadcast, or a Blu-Ray disk. A 720p television, by contrast, offers an upper limit of 1280x720 pixels, therefore, a significantly lower resolution.

"I," on the other hand, refers to "interlaced." It can be the same resolution as the "p" television, say, 1080, but the difference is in the way the picture is displayed. An interlaced display will scan the image onto the screen one line at a time, first the odd lines, then the even lines (this is how the old cathode-ray tubes also work - via odd/even scan lines). A "p" television, on the other hand, is what's called "progressive scan," and will display each line of resolution sequentially, in a single pass, which results in a smoother, cleaner image. This matters largely when there is a lot of fast action in the content - sports, or action movies, for example.

But all that said, the truth is, there is very little content available in true 1080p. Almost all high-def broadcast today is either 1080i or 720p, and bandwidth restrictions mean that probably won't change in the near future. Blu-Ray and Playstation games do offer higher-res content, and if you plan to hook your PC up to your display, you'll probably want to go 1080p.

Now how about the quality differences between plasma and LCD? This is an area of hot dispute. In the simplest, quickest terms: Plasma will offer better black levels (black will truly be black as opposed to some shade of grey); LCDs will be better when viewed with higher ambient light levels. And if you want to go BIG, you're going to want to look at Plasma. Plasma screens supposedly offer greater viewing angle, as well - you can be sitting at an acute angle to the screen and still see a decent picture.

While there used to be differences in the lifespan of the two TVs (plasma TVs would top out at about 20,000 hours), newer sets in both technologies will give you 60,000 - 100,000 hours - which, even at the 7.5 hours the average American TV is on, is still more than the 7 years most of us keep our TVs before replacing them with bigger, better and newer.

Plasma screens used to be susceptible to "burn-in," in which, particularly in the first 200 hours of viewing, a particularly strong and persistent image could "burn" into the display, so that an artifact of that image would remain on the screen from that point on. This really isn't the case in newer models. There is less chance for burn-in at all, and when it does occur, it's self-correcting and will disappear within a short time.

So what's the bottom line? The knowledgeable guys at CNET say, "If you're in the market for a big screen television — and we're talking 50 inches and above — then we'd suggest plasma as a safe bet. Plasmas give you more bang for your buck at the big end of town, and while LCDs can give you better resolution, plasma still has the edge in terms of picture quality. One other thing to look for, whether you opt for plasma or LCD, is an integrated HD digital tuner — some TVs still have analog tuners, which look pretty terrible on a large screen.

"At the smaller end of things (17-inch to 42-inch TVs), LCD is the only way to go if you want something slim and tasteful. And the best thing is that LCDs are getting cheaper all the time."

And as far as the 1080 vs. 720 choice, it's really a question of cost. If you can afford it, or if you plan on hooking up your display to your computer, go for 1080. Otherwise, for now, you'll be just fine with 720.