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High-definition television (HDTV) transmits TV signals digitally, in contrast to the analog signals that have been used for the past 75 years. Color resolution and picture sharpness are greatly enhanced with HDTV, and sound quality is also much improved through the use of Dolby Digital.
There is quite a bit of HDTV terminology, and it can be confusing for even tech-savvy consumers. With that in mind, we’ll provide an overview of basic HDTV technology here:
Types of Television Transmission
Analog transmission of television uses continually varying signals to broadcast and display picture and sound. Television programming has been transmitted in analog signals since its inception in the 1930s.
Digital television (DTV) is a generic term for any transmission of television using the computer code of 1s and 0s instead of analog varying signals. Digital television first launched in the U.S. in November 1998. The Federal Communications Commission has mandated a nationwide switch from analog to digital broadcasting by the end of 2006.
Standard-definition television (SDTV) is a basic digital TV transmission that can be broadcast with fewer than 480p lines in 16:9 or 4:3 aspect ratio.
Enhanced-definition television (EDTV) offers a better digital picture than SDTV and comes in at least 480p in 16:9 or 4:3 format. It also supports Dolby 5.1 digital surround sound.
High-definition television (HDTV) is the highest-quality digital TV available and transmits in either 1080i or 720p in 16:9 widescreen format. It also supports Dolby 5.1 digital surround sound.
Resolution: 1080i and 720p
1080i and 720p refer to the resolution that you see on your HDTV screen. An interlaced signal alternates the odd lines and even lines on the display in a very fast manner quicker than the human eye can see. A progressive scan image fills the entire display with every frame. The number before the “p” (progressive) or “i” (interlaced) symbol represents the number of vertical lines in the broadcast.
The majority of HDTV programming is transmitted in 1080i, although ABC, FOX and ESPN all broadcast in 720p. 1080i has 1,080 vertical lines of resolution and 1,920 pixels per line, while 720p has 720 vertical lines of resolution and 1,280 pixels per line. By way of comparison, DVDs have 480 vertical lines of resolution and 720 pixels per line and come in either the 480p or 480i format, depending on whether you’re using a progressive scan DVD player or not (which is irrelevant if you’re watching an analog TV). Analog television is broadcast in 480i.
The ultimate in HD resolution is 1080p, which offers full 1,920 x 1,080 resolution with progressive scanning. Many manufacturers now offer 1080p HDTVs, although no broadcasters yet have any programming in this format. The next generation of DVDs will offer 1080p resolution and should start to hit store shelves in late 2005.
When comparing screen resolution, keep in mind that most “HDTV Compatible” TVs can display both HDTV and EDTV, and they will convert the signal to fit the TV’s resolution. For example, plasma TVs do not natively display interlaced signals, so they cross-convert a 1080i signal into 720p. Additionally, resolution is not the only factor to look at when comparing HDTVs. In fact, there are some 42-inch EDTV (480p) plasmas that offer a high-quality picture. Other factors to examine when buying a digital TV include the black level, component inputs and speaker quality.
Aspect Ratio: 16:9 vs. 4:3
4:3 is the aspect ratio of analog television, while 16:9 is known as widescreen and closely approximates how most films are shown in the movie theater. The numbers represent units wide by units high, so a 16:9 widescreen is 16 units wide by 9 units high. Watching movies in widescreen when your TV is set for 16:9 nearly, although not entirely, eliminates the black bars at the top and bottom of the picture. However, programs broadcast in analog will still show up in the 4:3 ratio, even if your HDTV is set at 16:9, leaving black sidebars on each side of the picture. These can be eliminated by stretching or zoomingthe 4:3 picture so that it fits the 16:9 screen (see HDTV Ownership Tips).
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