HDTV, or EDTV?

In Circuit City's flier for its Fourth of July 2005 weekend sale, a brand-name-unidentified ("models may vary by store") 42" plasma TV is offered for just $1,499.99, after $300 "instant savings." It's shown as a Widescreen Flat Panel Plasma Enhanced Definition TV. That term, "enhanced definition" — what's up with it?

Enhanced definition television, also known as "ED television" or EDTV, is a level of picture detail less than true high definition but more than standard definition. Simple, huh?

The basic measure of picture detail is how many scan lines there are, plus how often they're updated or refreshed. In 720p HDTV, there are 720 horizontal lines on the screen, and they're all updated at once, every 1/60 second. The fact that they're updated all at once is called "progressive scanning." So HDTV is at least 720p, where 720 gives the number of scan lines and "p" (for "progressive") gives the method of scanning them.

Alternatively, HDTV can be 1080i: 1,080 scan lines, using "interlaced scanning." In interlaced scanning, the odd-numbered scan lines are refreshed in the first 1/60 second and the even-numbered in the second 1/60 second. Then the scanning process begins all over again.

Many of today's TVs use a number of scan lines between 720 and 1,080, such as 768. They convert 720p and 1080i to a scanning format compatible with that particular number of scan lines. In so doing, they generally wind up with a progressive-scan picture. Though they don't use either 720p or 1080i "natively," they're still high-definition, since their screen output format – call it, for instance, "768p" — meets or exceeds 720p.


Enhanced-definition TVs also use progressive scanning, à la 720p, but they use a number of scan lines less than 720. The typical number of scan lines is 480, so most EDTVs natively are 480p TVs.

Not coincidentally, 480p is the type of signal furnished by a progressive-scan DVD player. DVDs are encoded at 480i, which means there are 480 scan lines in the video frame, but they're scanned in the odd-even interlaced pattern, just like standard-def TV and 1080i HDTV. The progressive-scan player can "deinterlace" the two interlaced fields that make up each video frame. Deinterlacing works especially well when the DVD is based on movie material, since the player can basically reconstruct the original film's frames one at a time, in all their glory.

So an EDTV that uses 480 scan lines is a perfect partner for a progressive-scan DVD player. It can give you all the picture detail that's present on a DVD.

An EDTV can also accept and display 720p and 1080i signals. It's just that these truly high-def formats are "downconverted" or "scaled" to 480p by the EDTV, which means they lose a noticeable fraction of fine picture detail.

An EDTV can even accept 720p/1080i signals directly from an over-the-air antenna if it contains a built-in digital tuner. Such a tuner-equipped EDTV is sometimes called "ED built-in." Or, it can be called an "integrated EDTV." An "HD built-in" TV set or "integrated HDTV" is just the same, except that its output definition meets or exceeds 720p. Get it?


The second important aspect of enhanced or high definition television, vis-à-vis standard definition TV, is the widescreen, 16:9 aspect ratio. Standard-def TV is stuck with a squarish, uncinematic 4:3 aspect ratio.

Often, an EDTV is not identified as such in advertising, by any of its usual monikers. All you know from the ad, sometimes, is that it's widescreen, and that it's not labeled HD. If you look at the fine print, you may be lucky enough to find out what it's screen resolution is: say, 852 x 480.

The first number is (usually, but not always) the number of pixels (picture elements) across the screen in each scan line. The second number is the number of pixels high the screen image is. That number, not surprisingly, equals the number of scan lines. (In some TV models, sadly, I've seen the two numbers reversed. That can be confusing indeed.)

If you multiply the second number by the widescreen aspect ratio — 16:9, or 1.78 — you should get (roughly) the first number. This is because the pixels are usually square. Their width is the same as their height.


So an EDTV represents a viable option for folks who simply don't want to shell out the really big bucks for a pricey high-definition TV set just yet.

As I write this, Circuit City is selling a Panasonic 42" Plasma EDTV, model TH-42PD50U, for $2,250. This model is a step up in quality from the brand-unidentified one I mentioned earlier. Its 852 x 480 flat-panel screen can do wonders for DVD viewing at full resolution, and it casn also permit pretty-darn-good HDTV viewing at reduced resolution.

This plasma flat panel has a built-in digital tuner for over-the-air reception. This particular tuner is called an "ATSC tuner," in the jargon, since standard-def reception is always done with an "NTSC tuner." (The Panasonic also has one of those built in.) Notice the changeover from the first letter being "N," for standard-def analog TV, to the first letter "A" for extended- or high-def digital TV.

The Panasonic TH-42PD50U even is digital-cable-ready, since it also has a built-in "QAM tuner," the type of tuner that is used for digital cable as opposed to digital over-the-air reception. (In order to take full advantage of the QAM tuner, you will probably have to rent a credit-card-size "CableCard" from your local cable-TV company and insert it into a slot in the TV. Without the CableCard, you'll be able to receive unscrambled digital cable channels, but to view scrambled ones, you'll need the card.)

Oh, and here's one more little secret. If you buy an EDTV like the Panasonic TH-42PD50U, your friends and neighbors don't ever have to know it's not true hi-def!