The Specs Explained
Gone are the days when you figured out how big a screen you wanted, looked at some sets, and bought the one with the best picture that fit your budget. An options explosion has littered the shopping landscape with numbers, features, and terminology that even experts sometimes have trouble tracking. So we've tried to boil it down to the basics that can actually do you some good. (In audio and video, never forget that just because something has a number to describe it doesn't mean it really matters!)
We've divided the specs into three categories: important, somewhat important, and minor.
Important: Aspect Ratio
The aspect ratio describes the relationship of screen width to screen height. Conventional sets have a 4:3 aspect ratio, whereas wide-screen models are 16:9. Wide screen is the future. HDTV is a wide-screen format, for one thing. For another, DVDs usually look better on wide-screen displays because nearly every movie made in the last 50 years was filmed in an aspect ratio of either 1.85:1 (very close to 16:9, which is 1.78:1) or 2.35:1 (even wider than 16:9).
Somewhat Important: Resolution
For CRT displays, resolution typically is specified according to standard broadcast TV formats, such as 480i, 720p, 1080i, and so forth. The 720p and 1080i formats are high definition. Non-CRT displays, such as LCDs and DLPs, are fixed-pixel arrays, which means they have rows and columns of individual picture elements that turn on and off to produce the necessary patterns of light. Resolution is usually specified as the number of pixel columns by the number of pixel rows--640 by 480, for example, or 1280 by 720.
Perceived picture detail depends primarily on display resolution. Generally speaking, a display is considered high definition if it is wide screen and has a total pixel count approaching 1 million. So 1920 by 1080 (1080i or 1080p), 1280 by 720 (720p), and 1366 by 768 are all examples of high-definition display resolutions. Small differences are usually not very consequential; you would probably not see much, if any, difference between the three examples just cited unless you were sitting close to a large screen (say, less than 10 feet from a 50-inch display)--which is why we consider this spec only somewhat important. Since all current rear-projection TV models are high-definition displays, resolution is not the biggest point of differentiation among them.
Important: Video Inputs
The number and type of video inputs determine which sources you can use with the display.
Composite video: This input type has the lowest quality but the broadest compatibility. Any device that has video outputs will include composite video among them. Connection is made with a single 75-ohm coaxial cable between RCA jacks.
S-Video: S-Video offers better quality than composite video, and most video sources except standard VCRs now have S-Video outputs. Connection is made with a special cable and multipin sockets.
Component video: This high-quality option is the minimum standard for connecting HDTV cable and satellite boxes and progressive-scan DVD players. It requires three 75-ohm coaxial cables of the same type used for composite video.
VGA: Video graphics array is a high-quality analog RGB connection used for computer connections and sometimes in place of RGB+H/V.
DVI: This is one of the highest-quality types of inputs. Digital visual interface is a digital video connection that can link to devices with HDMI outputs (see below) by means of an adapter. It may also be used for computer connections. Requires a special cable and multipin sockets. Some displays with a DVI input may work only with computers, so watch out for that if you plan to connect an HDTV source, such as an HD digital cable box or an HD DVD or Blu-ray Disc player. Another thing you need for guaranteed HDTV compatibility is compliance with the HDCP (High-bandwidth Digital Content Protection) system.
HDMI: Also of the highest quality, High-Definition Multimedia Interface is basically DVI plus a digital audio and control link, and it normally incorporates HDCP; it can be mated to DVI with adapter cables. This connection is provided on almost all current HD satellite receivers, HD cable boxes, and upconverting DVD players (those that provide 720p, 1080i, or 1080p output from regular DVDs). It is also the standard video connector for HD DVD and Blu-ray Disc players. The exact version of the HDMI input (e.g., 1.1 or 1.3) is of little consequence on TV sets. If you have or plan on getting an HD DVD or Blu-ray Disc player, it is desirable, though not essential, that the TV's HDMI inputs be capable of accepting 1080p signals (most now are).
Important: Viewing Angle
Because of the nature of their screens, rear-projection TV images tend to lose brightness as you move away from directly in front of them, especially on CRT-based sets. The effect is usually more pronounced vertically than horizontally, but since people tend to watch from the same height all the time, the vertical fade is less important. How much the horizontal viewing angle matters depends on how your seating area is set up, but the closer a set gets to a 180-degree acceptable viewing angle, the better. And though a viewing-angle spec can be a handy rough guide, there is no substitute for checking this out with your own eyes.
Somewhat Important: Built-In Tuners
You can expect any rear-projection television to include tuners for conventional analog broadcast and cable TV reception and for broadcast HDTV. And it almost always will have a built-in tuner for digital cable TV as well. Although a standard for handling scrambled premium channels (for example, HBO) exists in such tuners, few sets support it, so be sure you know exactly what you are getting. If you want that capability, make sure the set you buy has a CableCard slot and that your cable provider can provide you with the necessary electronic ID card. Cable pay-per-view services and satellite TV currently require external set-top boxes.
Minor: Comb Filter Type
Comb filters are necessary in analog TV to separate color and luminance information without losing too much detail, but that's not an issue in HDTV. The only time the comb filter comes into play is for analog TV reception or any signal coming in through a composite video connection. For all other connections, it's out of the loop. Plus, the comb filters in today's rear-projection TVs are routinely very good.