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People who are interested in home entertainment today find themselves constantly bombarded with the term “HDTV.” Studies confirm that most of us are very confused about what the term actually means, much less how to experience the full benefits of high definition television in our own homes.
So what exactly is HDTV? Where does it come from? More importantly, how do I get it? Even if you think you know the answers to these common questions, this tutorial may come in handy.
A Word of Caution
What commonly passes for “HD” on the market is not always what it appears to be.
Example: You just bought an amazing LCD TV with 1024×768 screen resolution. Have you arrived in high definition heaven? Technically, the answer is no. In fact, your expensive new TV is about 135,168 pixels shy of the minimum 1280×720 pixels (that’s 1280 pixels across and 720 from top to bottom) that are required to meet the official HD standard.
In this series of articles defining HDTV we’ll look at the three primary criteria for attaining the definition high experience: Resolution, audio and programming. In this article we’ll discuss resolution, perhaps the most important element of defining HD.
Visual displays work by drawing a picture, line by line and dot by dot. The way these images are created on the screen depends on the type of technology in use – CRT, LCD, plasma, etc – however, the number of dots used to make the picture is what really matters when it comes to HDTV.
The term resolution is used to describe how much information the screen can display. In the case of a TV screen, this is usually stated in terms of how many lines it can show.
Most TVs in the United States are designed to display 480 vertical lines (the actual number of lines is slightly higher, but only about 480 lines show up on the screen). This is the way TV stations have broadcast their signal over the airwaves for more than 50 years. It is, in fact, a standard defined by the National Television Systems Committee, and therefore known as NTSC. It’s also commonly called Standard Definition, or SD.
High definition TV is answerable to a higher standard, namely, more lines: at least 720 lines, to be exact. HDTV can offer even higher resolution, as well. The highest of high definition — at least for the moment — is 1,080 lines.
So you’ve got standard definition and high definition, but what about the middle ground? The standards committees have that covered, as well. Enhanced definition (ED) lies between standard and high definition, requiring only 480 lines of resolution. ED is extremely popular among plasma TV buyers – in fact, EDTV currently represents the majority of plasma TV sold in the United States. The reason is simple: ED screens cost less to make, and therefore, less to buy.
“So,” you might ask, “if SD consists of 480 lines, and ED does, too, why is ED better than SD?” The answer lies in the manner in which the lines are drawn, or scanned, onto the screen. There are two methods: interlaced or progressive. Standard definition is made up of 480 interlaced lines (also known as 480i), while enhanced definition uses 480 progressive lines (480p).
Progressive scanning draws each line of the image in succession, creating a smooth, complete and flicker-free picture. Interlaced scanning is a method that draws every other line, then goes back and draws the ones in-between. It’s great for sending image information efficiently and economically over the airwaves, but interlaced scanning provides a picture that’s inferior to progressive scanning TV technology.
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Resolution can be expressed in lines, but with digital technologies such as LCD, plasma and microdisplay televisions, it’s more common to measure resolution in pixels. Pixels are the tiny dots of colored light that act as the basic building blocks of a TV picture. Since pixels are organized in a grid pattern, the number of horizontal lines is equal to the number of pixels in a vertical line, and vice versa. Example: If there are 480 pixels running across the screen horizontally, the screen will have 480 vertical lines. Likewise, if there are 640 pixels stacked up vertically, the screen will have that number of horizontal lines.
Most HDTV formats are generally referred to by the number of vertical lines — and whether those lines are interlaced or progressively scanned — i.e., 480p, 1080i, etc. However, the number of horizontal pixels also matters. In general, the more pixels, the better the picture.
In practical terms, certain types of TVs tend to have certain resolution levels, as follows:
- CRT TVs – Analog CRTs (cathode ray tubes) don’t really divide their horizontal scan lines into pixels. For this reason, most CRT TV manufacturers won’t quote the true native resolution in their documentation. In general, CRT technology is capable of displaying HD-quality video. Some tube TVs can even display full 1080p resolution. However, the process by which the images are created is essentially analog, so making a realistic comparison between a CRT display and a truly digital technology (such as plasma, LCD or microdisplay projection TVs, for example) is difficult at best.
- LCD TVs – Among digital TVs, flat-panel LCD (liquid crystal display) TVs come in the widest variety of screen resolutions. In fact, the U.S. retail marketplace currently offers 11 different LCD TV screen resolution varieties. The most abundant type – some 56% of all TVs offered for sale — is the 1366×768 variety, providing 720p HD capability with pixels to spare. There are 27 manufacturers who currently offer LCD TVs with native 1366×768 resolution at major U.S. retail chains (source: Current Analysis).
|LCD TV Screen Resolutions:||HD/ED/SD|
- Plasma TVs – These TVs run from 37 inches, up to more than 100 diagonal inches in specialty models. They also tend to be constrained to a much smaller, more manageable palette of screen resolutions. Partly, this is due to the fact that there are fewer manufacturers of the plasma screen component worldwide, so there tends to be greater standardization in screen size as well as resolution. While plasma TVs with 1080p (1920×1080 pixels) resolution are being manufactured in small quantities, none have yet been offered by U.S. retail electronics chains. As with LCD TVs, the most common screen resolution for plasma TVs is 1366×768.
- Rear Projection TVs (RPTVs) – Some RPTVs use CRT technology to generate their image displays, and so are subject to the same nebulous analog CRT resolution issues described above. All other RPTVs rely on a chip-based microdisplay technology, such as LCD, DLP or LCoS. LCD-base projection systemscontain small LCD panels. The miniscule pockets of liquid crystal material in the panels are constantly changing to allow or block light, turning pixels on and off to create the screen image. DLP originally stood for digital light processing, a technology created by chipmaker Texas Instruments. It uses processors with millions of tiny, pivoting mirrors that create pixels by aiming light onto or away from the screen. LCoS is a hybrid of both LCD and DLP, combining to best qualities of those display other microdisplay technologies (for more on LCoS, see “The Resurrection of LCoS”).
|Plasma TV Screen Resolutions:||HD/ED/SD|
|RPTV Screen Resolutions:||HD/ED/SD|
While 1080p (minimum 1920×1080 pixels) is currently the be-all and end-all of HDTV resolution, there isn’t actually a lot of benefit in owning one of these so-called “true HD” models at the moment. The problem is that no U.S. broadcasters are offering native 1080p content. Some TVs have processes that will “upscale” lower resolution signals to use all of the 2.07 million pixels. New video sources are on there way which promise to eventually provide native 1080p content – such as next generation high-definition DVD players and Sony’s highly anticipated PlayStation 3. In the meantime, consumers need to decide whether it’s worth the extra dollars to buy a “future-proof” 1080p TV now, or wait until they have access to source material that will really put those TVs through their paces.
In the final analysis, high resolution definitely sounds good on paper, but can your eyes really perceive the difference between a 1280×720 screen or a 1366×768 screen? The answer depends on the individual.
In future articles, we’ll discuss additional issues that define the high definition experience, including HD programming and multichannel audio.