11 Great Questions About HDTV (High-Definition TV)

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You’re likely to have many questions about HDTV before you make a large investment. Here are some answers to typical HDTV-related questions.

1. What Is the Difference Between Standard-Definition TV And High-Definition TV?

Standard-definition TV (SDTV) has a lower resolution than HDTV. Therefore, it has a lower quality picture. However, SDTV and HDTV use digital technology. The images on SDTV are of better quality than those of today’s typical TV screens and SDTV supports stereo sound. In technical terms, SDTV operates at resolution that’s comparable to computer VGA displays that operate at 640 x 480. Because of overscan and display differences most SDTV resolutions are rated at either 704 x 480 or 640 x 480. HDTV, however, operates at resolutions that range from 720p (1280 x7 20, with progressive scan that shows every line on the screen every time the screen is refreshed) to 1080i (1920×1080, with interlaced scan that shows every other line on the screen every time the screen is refreshed).

Enough tech talk. The improved resolution of HDTV is just one benefit. HDTV also offers a wider 16:9 aspect ratio for images than does SDTV (4:3). The wider ratio more closely resembles the aspect ratio used when filming movies (and thus, allows more of the original field of view to be seen on screen). HDTV includes support for multi-channel surround sound (usually 5.1, which means front left, center and right channels, left and right surround, and a low frequency effects channel for deep bass sounds) that offers a richer, more immersive listening experience – if you have the proper equipment to play it back.

2. What Size Screen Is Best For Viewing HDTV?

Most TV experts offer the following formula to determine HDTV set size: take the distance between your primary viewing seat and where the set will be located, and divide by the screen size. The ratio of the screen size to that distance should be no less than 1.5 and no greater than 2.5. Table 1 shows typical screen sizes and viewing distances so you can see how this translates.

Table 1: Suggested Set Sizes For Viewing Distance Ranges

Minimum
Distance

Maximum
Distance

Suggested size
(diagonal)

3.75 ft 6.25 ft 30 inches
4.25 ft 7.00 ft 34 inches
4.60 ft 7.71 ft 37 inches
5.25 ft 8.75 ft 42 inches
5.88 ft 9.79 ft 47 inches
6.25 ft 10.50 ft 50 inches
7.00 ft 11.75 ft 56 inches
7.75 ft 13.00 ft 62 inches
8.75 ft 14.75 ft 70 inches

 

3. Why Don’t All TV Programs Fill the Whole HDTV Screen?

Unless you use upscaling technology (see question #11), SDTV displays at its native 4:3 aspect ratio on a 16:9 HDTV display. The result is a picture that fills the screen from top to bottom, but that shows a black area on both the left and right sides of the picture. That happens because the TV set normally scales the image to fill the pixel space on the display as best it can without changing the aspect ratio. Essentially, because SDTV is a narrowscreen medium and HDTV is a widescreen technology, SDTV broadcasts result in screens that are incompletely filled.

4. What Screen Resolutions Are Available For HDTVs?

The resolutions that match broadcast HDTV are 720p (1280×720) and 1080i (1920×1080), and high-definition DVDs offer a resolution of 1080p (also 1920×1080), where “p” stands for progressive scan, and “I” for interlaced scan. Progressive scan simply means that every line is displayed on the screen each time the screen is refreshed at the frame rate in use. Interlaced scan means that every other line is displayed on the screen each time the screen is refreshed. Now you see why 720p and 1080i look almost identical to the human eye. The most common HDTV resolutions appear in Table 2 (note that some 1920×1080 sets are now available, but that by no means do all HDTV sets offer this resolution). Most experts believe that true 1080p capability is only meaningful in sets 50 inches in size or greater, because of the distances between the viewers and the sets such screen sizes allow. Therefore, those who want (or think they might want) to view high-definition DVDs in their native resolution (1080p) may prefer to acquire 1080p capable sets.

Table 2: Common HDTV (Or HD-ready) Set Resolutions

Size

Type

Resolution

20″ LCD 1024×768
37″ LCD 1366×768
42″ LCD 1920×1080
45″ LCD 1366×768
52″ LCD 1920×768
57″ LCD 1920×1080
65″ LCD 1920×1080

 

5. What’s the Difference Between 1080i And 1080p?

Questions about HDTVThe technical difference is that only 540 lines get refreshed on screen at 1080i each time the screen is refreshed (which corresponds to the frame rate for video information), whereas all 1080 lines get refreshed for every frame at 1080p. The perceptual difference between these two formats is discernable only on equipment that can generate or handle 1080p content, but in that case it’s definitely noticeable: much sharper images, deeper colors, more solid blacks, and brighter whites are all among the differences that experienced viewers report between these two formats. There’s a definite cost difference between these two formats, however, because viewing content at 1080p usually means acquiring new players or set-top boxes to handle the content and new HDTV sets to display it (with new AV receivers in-between if the whole setup is part of a home theater). That probably explains why most people wait until they’re upgrading their systems to make the jump to 1080p.

6. What Resolutions Do HDTV Signals Use? DVDs? Hi-def DVDs?

Over-the-air (OTA) HDTV typically comes either in 1080i (CBS, NBC, PBS) or 720p (ABC, Fox). Premium networks use mostly 1080i (HBO HD, Showtime HD, Discovery HD, HDNet, and INHD) though ESPN HD uses 720p. All major cable companies and most satellite providers use 1080i resolution. As we write this FAQ, only HD-DVD and Blu-ray DVDs can deliver 1080p video signals to a display for viewing.

7. What Kind of HD Content Is Available?

Many different sources for high-definition content are available for your HDTV. They include high-definition DVDs (which require special players that conform to either the HD-DVD or Blu-ray DVD specifications), over-the-air HDTV broadcast content, HDTV content from cable or satellite TV providers, and various Internet sources or feeds (some free, some available only to paid subscribers) that offer HDTV content.

8. What Kinds of Digital Connections Support HDTV?

When you look at the back of a modern high-definition television set nowadays, you’ll see a plethora of connectors on the back. But although most such sets support direct coaxial cable inputs, as well as composite (single RCA connector), component (three RCA connectors in red, green, and blue), and S-Video (4 or 5 pin DIN connector), only two types of connections deliver all digital signals to your TV set: DVI (the digital video interface, a connector familiar to most PC users) and HDMI (the high definition multimedia interface, a compact connector that routes digital video and multichannel digital audio between pairs of devices). Those that deliver digital signals are the best for HDTV and should be used whenever possible.

9. What’s the Story With HDMI?

HDMI combines digital video and audio data into a single data stream, and reduces the cable tangles that so often converge around home theater gear, especially receivers and TV sets. This high-definition multimedia interface comes in two forms: one that looks like (and is compatible with) the digital video interface (DVI) used on many computers, and another more compact format (called the Type A) connector.

10. What Is Video Upconverting?

Various bits of video playback or processing equipment, including players or recorders (DVD or DVR), AV receivers, and television sets can employ special circuitry (often called a scaler chip) that converts video resolution to a format higher than whatever the input format might be for display. This means that you can have a confusing array of settings to get the best picture out of your system, and you will need to make some adjustments to these settings.

11. What Is Video Upscaling?

As opposed to upconverting, video upscaling refers to the process whereby a picture may be resized from one set of dimensions to another. Thus, for example, many HDTV capable set-top boxes can “stretch” an SDTV picture that ordinarily fills less than the full HDTV screen to cover the entire viewing area (though the aspect ratio is by necessity reset from 4:3 to 16:9 in the process, and image elements may look stretched, especially in the horizontal dimension) as a result. Some viewers prefer to watch the larger image that results from upscaling, while others prefer to maintain native resolution so as to also maintain native aspect ratios and image appearance. That’s a judgment call that varies from viewer to viewer.

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