HDTV - Basic Overview

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What is HDTV?

HDTV stands for High-Definition Television. HDTV is the new standard of television viewing. The hallmark of HDTV is the rectangular "Wide" screen and the high resolution of display. From the consumer’s perspective, HDTV translates to better visual and acoustic enjoyment to TV viewing. HDTV is an upgrade of digital technology from analog technology. HDTV is a digitally delivered signal whereas Standard Definition Television (SDTV) had historically been delivered as an analog signal; however it is now being delivered digitally in many cable and satellite systems. An HDTV signal provides six times the number of pixels than an SDTV signal, resulting in a much sharper image on the display. There is a class of digital television that is getting a lot of press right now. It is called High-Definition Television, or HDTV. HDTV is high-resolution Digital television (DTV) combined with Dolby Digital surround sound (AC-3). HDTV is the highest DTV resolution in the new set of standards. This combination creates a stunning image with stunning sound. HDTV requires new production and transmission equipment at the HDTV stations as well as new equipment for reception by the consumer. The higher resolution picture is the main selling point for HDTV. Imagine 720 or 1080 lines of resolution compared to the 525 lines you are used to in the U.S. (or the 625 lines in Europe) -- it's a huge difference!

Benefits of High Definition Picture and Sound

Much like the advent of color TV, High Definition dellivers an enhanced viewing experience. High- Definition offers Digital superiority, amazing detail, digital surround sound audio, better quality DVD playback and so on. It's no wonder why HDTV is one of the hottest selling electronics in the country. Once you experience it, you'll get it. A few details behind the power of HD:

The Shape's the Thing: Aspect Ratio

Aside from dramatically improved picture quality and multi-channel digital sound, the most noticeable difference between HDTV and other TVs is the shape of the viewing area which is defined by the aspect ratio. The almost square aspect ratio that has been used so extensively for decades is 4:3 -- the screen is 4 units wide for every 3 units high. By comparison, the HDTV specifications call for the aspect ratio for high-definition viewing to be 16:9, much like a movie theater screen.

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While the HDTV standard specifies the 16:9 aspect ratio, not all 16:9 television sets are capable of receiving HDTV signals. It's important to confirm that the set you are considering will actually receive and display high-definition television. Check the specifications carefully.

Windowpane, Letterbox and the Stretch and Zoom Solution

When you view 4:3 content on a 16:9 HDTV display, you may get an onscreen image with vertical black or gray bars on each side of the image. This is called a windowpane screen.

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Likewise, when 16:9 content is viewed on a 4:3 display, you may see a long and narrow image with the black or gray bars above and below. This is called a letterbox screen.

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Stretch and Zoom Solution

One pleasant viewing capability of HD cable set-tops is picture "stretch and zoom." This enables you to eliminate the black or gray bars and fill your HD screen with a non-HD video image rather than have it squeezed into letterbox or windowpane formats.

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Why HDTV Looks So Crisp and Sharp

Understanding what resolution means to picture quality will make you a more savvy high-definition buyer. In television terms, resolution refers to the clarity of the screen image based on the number of pixels on the screen. HDTV is the clear winner on resolution. For example, the image on an older 4:3 aspect ratio screen typically is divided into 480 lines, each with 720 pixels. An HDTV with 1080 lines with 1920 pixels in each line has six times the pixel density. The image on the screen can be created using two different scanning methods: interlaced and progressive. The "p" or the "i" you see in terminology such as 720p or 1080i refers to the type of scanning used (progressive or interlaced) and the numbers identify how many viewable on-screen lines the TV offers. As the number gets larger, the screen has more lines and more pixels to deliver a sharper, more vivid image.

Interlaced Scanning

On most TV screens anyone has watched for the last 50-60 years, the image is created using interlaced scanning. The lines on the screen are divided into two sections called fields -- one field includes the even numbered lines, the other the odd lines. So, each field (the even and the odd) contains half of the image to be displayed.

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In rapid succession, all of the odd numbered lines of the picture are painted onto the screen in about one sixtieth of a second, followed by the display of the even numbered lines in the next sixtieth of a second. Each new image is displayed so quickly that your eye is unaware of the process that's creating the video image.

Progressive Scanning

Instead of combining two fields to display a complete image, progressive scanning treats all the lines as one field and displays them in one sixtieth of a second. This speedy delivery of the entire image on the screen gives a more consistent-looking, clearer picture Now that you know the Basics of HDTV, you can learn more by taking an HDTV Tour or clicking on the "Beyond the Basics" tab. Or, if you have more questions, check out Frequently Asked Questions (FAQs).