Choice 1: Overview and resolution
| Meet Robert Harley
Harley is the Editor of The Perfect Vision and The Absolute
Sound, and one of the world's leading experts of consumer
electronic technology. He's worked as a recording engineer,
CD mastering engineer, and technical writer. Robert
holds a degree in Recording Engineering, and has taught
a college degree program in that field.
a celebrated author who has published more than 600
articles on audio and home theater, including reviews
of more than 350 products. His two books, "The
Complete Guide to High End Audio"and
Theater for Everyone: A Practical Guide to Today's Home
Entertainment Systems", are
considered reference works for the industry, with more
than 100,000 copies in print in three languages. He
has written or co-written several papers presented at
international Audio Engineering Society conventions,
covering topics as diverse as CD mastering technology
and evaluating audio products through critical listening.
| Additional Reading:|
Before buying a new analog television, you should know that the federal government has mandated that all television stations stop broadcasting conventional analog television signals at midnight on December 31, 2006. This mandate, however, applies only if 85% of American homes can receive digital television broadcasts-an unlikely scenario. Still, it could mean that there will be no over-the-air signals to receive on your conventional TV by 2007. If you want to continue using your analog set past this date, you must buy a digital television (DTV) set-top box that can receive the new digital television broadcasts and convert them to analog. Although the set-top box may be able to receive and decode HDTV signals, your set's picture quality will be roughly the same as it is today. Downconverted HD signals will look at least as good as DVD when using component-video connection between the digital-to-analog converter and your TV.
One way to avoid this situation is to buy an HDTV set now. The cost of HDTV sets has dropped dramatically since their introduction, and prices will continue to decline. Small direct-view HD sets are considerably more expensive than a comparably sized TV sold at a department store, but HD rear-projection televisions are only a few hundred dollars more than their analog counterparts. In fact, it makes no sense to buy an analog television today.
If you decide on a direct-view HDTV set, be wary of inflated marketing claims and confusing terminology; many sets billed as "HDTV" don't have the full resolution required to display high-definition signals. Moreover, the terms "HDTV-Ready," "HDTV-Compatible," and "HDTV-Capable," can display true high-definition signals, but simply lack an integral HDTV tuner. Such sets require the purchase of a separate set-top box (described in Chapter 3).
There are two key HDTV specifications. First is the number of vertical lines the set can display, called the set's vertical resolution. 480-line progressive (480p) is considered standard definition; 720-line progressive (720p) and 1080-line interlaced (1080i) are true high-definition. Second is the number of pixels on each line-the set's horizontal resolution. A pixel is the smallest piece of information in the picture; the greater the number of pixels, the higher the resolution, all other factors being equal.
This topic confuses even industry pros, so I'll state it another way. The horizontal resolution is the number of pixels the set can resolve on each horizontal line; the vertical resolution is the number of horizontal lines per video frame. In standard-definition NTSC television, the vertical resolution is absolutely fixed at 480 lines. That's the number of scanning lines that make up the picture. The horizontal resolution- the number of pixels the set can resolve on each horizontal line-varies with the quality of the set. In HDTV, the vertical resolution is absolutely fixed at either 720 lines or 1080 lines. That's the number of scanning lines that make up the picture. The horizontal resolution-the number of pixels on each horizontal line- varies with the quality of the video display. Vertical resolution is fixed by the format; horizontal resolution if a function of the video display.
There can be some additional confusion in the horizontal-resolution specification. When refering to fixed-pixel displays or the resolutions of digital-television formats, the term "pixel" is correct. When refering to an analog television's horizontal resolution, the term "TV Line" (TVL) is more appropriate. This specification is the number of vertical lines the television can resolve per picture height. If the set is driven by a signal of closely spaced alternating black and white vertical lines, we count the number of visually resolvable lines to determine the set's horizontal resolution. As those vertical lines become more closesly spaced, they eventually turn into a gray blur. The threshold at which the individual vertical lines are still resolved is considered the set's horizontal resolution in TVL. Don't confuse these vertical lines with the horizontal scanning lines of a television. The number of horizontal lines is fixed at 480 in NTSC video, and can by 720 or 1080 in HDTV. (NTSC is actually 525 lines, of which 480 contain picture information. The other 45 lines are not displayed on the screen, and contain synchronization pulses, and information such as Closed Caption data.) The 480 lines you see are called active scan lines.
Many manufacturers grossly inflate their sets' horizontal resolution specification, with some even claiming the product can display the full 1920 x 1080 resolution of HDTV. When considering marketing claims of horizontal resolution, think about this: a professional direct-view HD monitor that costs $40,000 has a horizontal resolution of just 1400 lines. Moreover, its light output is so low (0.5 foot-lamberts, or one sixtieth the brightness of a conventional consumer monitor of the same size) that it must be viewed in a virtually pitch-black room. Even then, the image is still dim. There are no standards to which manufacturers are held when making claims of horizontal resolution, so take the number with a grain of salt.
Direct-view sets have the lowest horizontal resolution of all high-definition video displays. Pixels in a direct-view set are formed by phosphor stripes that emit light when struck by the scanning electron beam that traces each line of video. Small phosphors allow higher resolution, but at the expense of light output. Consequently, designers of HDTV sets must trade away some resolution so that the picture is bright enough. That's why the $40,000 professional monitor's light output is almost unusably low.
The highest-resolution HD signal is 1920 x 1080, meaning the image is composed of 1920 pixels on each horizontal line, with 1080 vertical lines per video frame. Multiplying these numbers gives us a pixel count of just over 2 million pixels. We've seen that direct-view televisions can't come close to resolving this number. But how much resolution is needed for the picture to be called "high-definition"? There's no concrete threshold for calling a display "HD," but 1200 x 1080 pixels delivers about 1.3 million pixels, the point at which the video image makes the transition from looking very good to looking spectacular. (For comparison, a conventional analog television displaying a signal from VHS tape has a resolution of 240 TVL x 480. DVD provides a resolution of about 720 x 480 in theory, with a slightly lower number in practice.)
Although 1.3 million pixels falls short of HD's maximum resolution, the direct-view set can still provide a picture of phenomenal resolution because of its relatively small size. The smaller the picture (and the greater the viewing distance), the fewer pixels needed to produce a great-looking image. When we get into larger-image video displays later in this chapter, we'll see how resolution becomes more important with large image size than with the relatively small images produced by direct-view TVs.