HDTV Technology

In 1996 the FCC approved 18 different television resolution standards, although there are only four that seem to be the ones that will inhabit the airwaves for the foreseeable future: They are as follows:

480i (analog TV), 
480p, 
720p (HDTV),
1080i (HDTV)

These standards designations are made up of two components, a number and a letter: the number of horizontal scan lines and how the picture is "drawn."

The designation 480i, for example, is telling us that the television picture is made up of (approximately) 480 lines of information called horizontal scan lines. The "i" indicates that the picture is being put together by a process called interlace scanning. The designation 480p, on the other hand, indicates the picture is put together using progressive scanning.

Horizontal Scan lines
The pictures on analog TVs are made up of 525 horizontal scan lines*. But since some of those lines are used for things other than the picture, the truth is that the total is closer to 480 horizontal scan lines, which is why the standard is called 480i and not 525i. Regardless of the video source, -DVD, laser disc, antenna, satellite, or VCR, -the picture on analog TV is always made up of about 480 lines of information.

*confusingly enough, horizontal scan lines are not the same thing as horizontal lines of resolution, a measure of picture detail. Horizontal resolution measurements using today's technology can range from 250 for a VCR to as much as 500 for DVD or DIRECTV satellite. Unfortunately, now that you've bothered to learn this, horizontal lines of resolution cannot be used to measure the detail of an HDTV picture. Instead, horizontal scan lines will serve double duty by telling us how many lines of information make up the picture, as well as the potential level of detail.

The first color broadcast standard (NTSC) from 1953, has had the same 480 horizontal scan lines for over 50 years on analog TV even though better technology has been available for decades.

High-definition HDTVs and HDTV monitors (which require a separate set top box to receive HDTV broadcasts) are able to show images with 720 and 1080 horizontal scan lines.

Now that you know what the numbers mean, let's look at what the letters mean.

Interlaced (i) vs. Progressive (p)
This refers to the way in which the TV picture is put together. On analog TV, the 480 lines of information that create a picture on your TV screen are put together in an odd-even pattern called interlacing. First the odd lines of the picture are placed on screen (1, 3, 5, etc.) and then the even lines (2, 4, 6, etc.). This process is done continually and so quickly (30 complete frames every second!) that we perceive them as full motion.

The other way to "paint" a picture on a screen is a method called progressive scan, and it's found only on HDTVs and HDTV monitors (and some DVD machines) because only digital broadcasts and sources like DVD players send a signal this way. 

Like computer monitors, progressive scan creates a picture by scanning the lines in order, all lines at the same time (1, 2, 3, etc.). The way the picture is created is just one factor that determines picture quality. But that one factor is a big deal when it comes to DVD players. You see, more and more DVD players have progressive scan outputs that are designed to connect to an HDTV or HDTV monitor. You think you've seen DVD at it's best? Wait 'til you see your favorite movies on an HDTV with a progressive scan picture.

Pixels
Pixels is short for "picture elements" and they're the little dots of color that make up a TV picture. In fact, one really close look at a picture in a newspaper or magazine will show you how enough dots can create a picture. Of course, there's a pretty big difference between the picture quality of a picture in a magazine and a color picture in a newspaper. One of the reasons for this is the number of dots that make up the picture. You have to look pretty closely at a magazine picture to see that it's made up of tiny dots, but the dots in a newspaper picture are much more obvious-in part because there are fewer of them. The point of this little experiment is that the more dots (or pixels on a TV screen) that make up the picture, the clearer and sharper the image.

Analog TVs make a picture using up to 200,000 pixels. That's a lot of little dots, but this is one of those rare instances where more is just plain better, -widescreen HDTVs and HDTV monitors have 2,000,000 pixels, ten times more. Those extra pixels are capable of creating a picture that's ten times sharper than any TV picture you've ever seen on analog (NTSC) TV.

Aspect Ratios
Analog TVs are roughly square. If you were to express their shape using a ratio it would be 4:3; it's a little wider than it is tall. When you go to the movies you may have noticed that the screen is significantly wider than it is tall, and that's expressed as 16:9. You may have also seen a 16:9 picture on your current TV in a format called letterbox.

Letterbox lets you see a widescreen picture like you'd see in a movie theater on your roughly square TV by using the entire width of the screen, but not the entire height of it. This leaves you with black bars on the top and bottom of the screen, but more importantly it lets you see the whole picture. It should come as no surprise that movie directors are wild about the letterbox format because it is the only way you will ever see the picture they wanted you to see on your 4:3 TV. For this reason, some videotapes and virtually all of the DVD movies you can buy or rent offer the letterbox format.

Many HDTVs and HDTV monitors have wider screens that can use the entire screen to show widescreen movies and TV shows (without the black bands!).

We've covered the picture, now what about the sound
The phrase "CD-quality sound" is overused these days, for sure, but it's absolutely accurate when it comes to HDTV broadcasts. The sound you're used to from your analog TV is broadcast just like FM radio. Remember the first time you heard music on CD? Compared to the records and tapes you were used to it was like the musicians were in the room with you. Just wait 'til you hear how much better movies, music, and your favorite TV shows sound with a digital audio signal**.

In addition to sounding clear, some HDTV broadcasts will carry audio signals in a surround sound format called Dolby® Digital. With the right home theater equipment, Dolby® Digital can recreate surround sound effects from five different speakers in a dizzying array of combinations. This means that Dolby® Digital is capable of convincing your ears that a bullet is coming from the front left, whizzing by your head on its way to the left corner of your room. Or, if you prefer less violent fare, it can convince your ears that you're in a forest and the cricket you hear is behind you to your right.

Digital Video Interface
Digital Video Interface (DVI) is a port by which a single DVI cable connects a video device, such as a DVD player or other HDTV component, to an HDTV or HDTV-ready TV. This connection is important to HDTV picture integrity because DVI supports HDTV's high-resolution video. These visual capabilities are far superior to analog interfaces, such as Composite video, S-video, and even Component video, and can bring you visual performance unlike anything available before.

DVI has been widely supported and adopted by the TV industry as the ideal means for channeling digital TV signals. DVI also allows for an analog connection, but soon this won't matter; through a federal mandate, all TV broadcasts will have to switch over from analog to digital in the near future.