High-Definition TV Facts
High-definition TV (HDTV) is all the rage these days, but it's hard to pin down exactly what the term means. HDTV is sometimes confused with digital TV--a connected but not necessarily synonymous term--and not every TV can pick up a high-definition broadcast. By understanding the facts about HDTV, you can select the equipment that will help you make the most of your viewing experience.
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Standard Resolution
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"High definition" refers to the resolution of the image. A standard television shows the image with a resolution of 480i, which means that 480 vertical lines of pixels make up the image onscreen. The "i" stands for "interlaced," which means that the screen quickly flickers back and forth between one half of its lines and the other half. (A "p," which stand for "progressive," means that all of the pixel lines broadcast at the same time.)
HD Resolution
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With the advent of high-definition television, resolution has increased a great deal. Plasma-screen and LCD-screen TVs can now show images in 720i, 720p, 1080i or 1080p depending on the model. The last number constitutes true HD television: 1080 vertical lines broadcast progressively (i.e., all at once). It produces an exceptionally sharp and clear image: twice as sharp and clear as standard resolution televisions.
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Advanced Technology
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High definition became possible in part through a change in the screen's technology. Older TVs used a cathode-ray tube to broadcast their images--which accounted for their bulky, boxy appearance and limited their image resolution to standard levels. New TVs use individual cells filled with plasma or liquid crystal displays sandwiched between glass--both of which allow for additional pixels on the screen and thus higher resolutions.
Broadcast Signals
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HDTVs allow for the reception of high-definition signals. If the signals aren't sent in HD, then the image won't be broadcast in HD, even if you have an HD television. You can tell if a show is broadcast in HD, usually by the little "HD" symbol next to the schedule listing or flashed on the screen when the program begins. Shows that don't have that symbol are broadcast in standard definition. Shows broadcast in HD include prime-time network shows, high-end cable shows such as "True Blood" and "The Closer," and sporting events like the World Series and the Super Bowl.
Digital vs. HD
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High-definition broadcasts wouldn't be possible without digital technology, which is where some of the "digital/HD" confusion comes in. Digital signals use a binary code (basically a series of 1s and 0s) which take up much less space on the bandwidth than the older analog signals they're replacing. The use of less space means more information can be packed into the bandwidth, which allows the images to be broadcast in high definition. A digital signal doesn't guarantee that you'll see a program in HD, however. A TV that can receive digital signals may still have a standard-definition screen connected to it.
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