Display Technologies

CRT: Cathode ray tubes are used in direct-view TVs (one tube) and some front and rear projectors with three tubes or "guns" for red, green and blue. CRT can produce the most filmlike images, but it's an aging technology that is being replaced by others that don't require a bulky and heavy chasses.

DLP: Digital light processing has made both front and rear projection systems much smaller, lighter, portable and affordable. It works by reflecting light off of thousands of microscopic mirrors embedded on computer chips. More-expensive DLP front projectors use three chips to produce red, green and blue, while less-expensive single-chip front and rear projection sets spin a color wheel in front of the reflected light to produce the full spectrum of colors. New HD-4 chips use in excess of 1.3 million microscopic mirrors that switch on and off more than 50,000 times a second to provide excellent motion video with virtually no artifacts or image streaking. A handful of models will also offer 1920 x 1080 pixel resolutions, which translates into 1080p.

LCD Projection (3LCD): Rear projection LCDs utilizes three LCD wafers and a powerful lamp to throw an image onto a screen with one lens instead of three. While these sets offer an extremely fine picture, there can be some contrast problems, though these have been addressed effectively in recent years. LCD projection has recently been renamed to 3LCD to denote the fact that it uses three LCD wafers, one for each primary color (red, green and blue).

LCoS: With liquid crystal on silicon front and rear projectors, liquid crystals are coated onto silicon chip, which uses a reflective layer to greatly increase contrast and eliminate any dotted or "screen door" effect. Because it is a digital display device, LCoS technology also eliminates any chance of image burn-in. LCoS is available in one and three-chip designs. Three-chip models provide true 1920 x 1080 pixel resolution (1080p). There have been production problems with this technology, but that could change this year.

D-ILA or HD-ILA: Direct image light amplifier (D-ILA) is related to LCoS and is designed for high-brightness/high-resolution large screen displays. It is capable of displaying more than 3,000 lines of resolution with images in excess of 2,000 x 1,340 pixels. Presently, JVC is the only brand utilizing D-ILA technology in both front-projection and rear-projection models.

SXRD: Sony's Silicon Crystal (X-tal) Reflective Display is a variation on the LCoS technology and is available under its new Qualia brand as both a high-definition home theater projector and a 70-inch rear projection model. It displays images at 1920 x 1080 or 1080p.

Direct-View LCD: Liquid crystal displays in flat panels work by trapping a liquid crystal solution between two sheets of polarized glass and passing an electric current through the liquid crystals. Most LCD panels are backlit. For clear, crisp color that rivals traditional CRT displays, a thin film transistor (TFT) is employed.

Plasma: A plasma display panel (PDP) features two glass plates meshed together like a sandwich and filled with an inert gas, while electrodes selectively illuminate gas-filled cells. The pixels act like microscopic lightbulbs. There is uniform screen brightness and unlike a conventional picture tube; no "hot spots."

High-Resolution, Not Confusion

Display devices come in different resolutions that simply denote the sharpness of the picture by the number of lines or pixels on the screen.

There are several types of HDTV formats. Two of the more popular are 720p (for 720 lines of progressive scan rate) found on most flat-panel display models and 1080i (for a scan rate of 1,080 lines interlaced), which is found on most CRT-based products and many microdisplay devices using technologies such as DLP and LCD.

So is 1080i better than 720p? Not necessarily. The 1,080 lines in 1080i are interlaced, meaning only half of them show on the screen at any one time, though it switches so fast it tricks your eyes into seeing all of them there. In 720p, the 720 lines are progressively scanned so they are all there at any time, and they fully replenish even faster. For this reason, some experts believe 720p is better suited than 1080i for displaying fast-action sports and the like. Though for most people, the difference is unnoticeable.

The newer HDTV format ends all debate: 1080p translates into 1,080 lines of progressive scan rate, which will be found on some flat-panel and microdisplay products this year.

Finally, if you're shopping for an HDTV, check the display's "native resolution." It will be a number such as 1280 x 768 (indicating the horizontal by vertical resolution). The second number shown must be 720 or above for the set to be able to display high-definition images. If it isn't, it simply isn't high-def!

All About Screens

• Front video projectors come in two pieces: the projector itself and the film screen. The screen is sold separately. Quality film screens can cost upwards of several thousand dollars, depending on type and size.
• A filmscreen is a thin piece of woven fabric that is covered with an optical coating. The screen is comprised of the material and the housing or frame. There are four common aspect ratio sizes: 1.33 (traditional TV), 1.78 (widescreen HDTV), 1.85 (letterbox video) and 2.35 (CinemaScope).
• Screens are available in fixed frames, with or without a masking system to alter the aspect ratio or screen shape, and with electrical roll down that can add several hundred dollars to the cost. Screen sizes normally range from about 60 inches to more than 160 inches wide. You can also order screens from most companies in any size and aspect ratio you wish for an additional fee.
• Check the screen's gain. This is a relative measure of a screen's reflectivity and relates to the perceived brightness. A 2.00-gain screen reflects back more light than a 1.00-gain screen. The higher the gain, however, the narrower the viewing angle.
• A variety of materials are used on screen surfaces. Before selecting a screen, you should first consider the projector type and model, viewing angles, ambient light conditions, seating layout and screen size.
• Matte white is the standard by which all other surfaces are compared. Its surface evenly distributes light over a wide viewing area. The colors remain bright and lifelike, with no shifts in hue.
• High-contrast matte white is designed for the moderate output of DLP and LCD projectors. This screen surface is a good choice where ambient light is moderately controlled.
• Glass-beaded screens are used to obtain high reflection but with a narrower viewing area. All glass-beaded surfaces have some loss of clarity and may perform best with table-mounted projectors.
• High power reportedly provides the highest gain of all front-projection screen surfaces with no loss of resolution.
• Video spectra surfaces have reflective coatings and are suitable for environments where ambient light is uncontrollable.
• Some materials are also available in acoustically transparent versions that conceal speakers placed behind the screen, though the tiny holes reduce brightness.
• A gray screen helps to enhance black levels of DLP and LCD projectors. There is even a new black screen technology that allows front video projector viewers to watch movies in less-than-darkened rooms by reflecting only the light from the video projector.
• Last, screens can also be THX and ISF (Imaging Science Foundation) certified. Check with your local electronics dealer to learn about the most appropriate screen for your home theater.

• See the parent article, "The Really Big Picture"

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