How to choose a video or data projector

The most important specifications

• Resolution measures the amount of detail that can be seen in an image. For computers, resolution is expressed in the number of pixels down and across the screen, and it's important that your projector is capable of matching the resolution of your computer system. VGA requires 640 x 480 resolution, S-VGA 800 x 600, XGA 1024 x 768. Standard 13" Macintosh monitors use 640 x 480 resolution, but to show a 17" Mac monitor full-screen requires 832 x 624. Engineering workstations can require even higher resolutions. For this reason, the resolutions of three-tube projection systems are normally expressed in scan rate ranges, to allow you to match them to the workstation or specialized graphics card you may use.

• For video, resolution is expressed as the number of lines per inch visible on a test pattern. The video resolution specification (which is not the same as the horizontal computer resolution—and actually is determined more by the electronics of the projector than by the LCD panel) can serve as an overall indication of the video quality you can expect.

• Brightness. As you start to compare LCD projectors, you'll need to know the brightness in ANSI lumens (the current ratings standard, and, please note, not comparable to "lumens" expressed in non-ANSI terms). As a rough guide, a rating of 600 - 800 ANSI lumens works well with a 100" to 150" diagonal screen with lights dimmed, but you'll want at least 1,000 ANSI lumens when you go to larger screens and 1,500 or more if you want to project in bright lighting conditions. Your best bet, of course, is to ask your sales rep to demo the LCD projector under conditions typical to what you'll see.
  

• Size and weight. There's often a trade off between small size and image quality. If you depend on a sales force to voluntarily take your projector and program from call to call, you may find an ultra-compact LCD is your best bet, as an expensive multimedia production does no good sitting in a closet or a car trunk. Others may find, however, that a 12 to 15 pound LCD projector offers a better combination of brightness and price, yet is still very portable. Naturally, if you're going to put the projector on a cart or a ceiling mount, size is much less important.
  

• Your video source. Do you need to show S-video or just standard composite video? Will you take the unit overseas (and thus need the ability to accept PAL or SECAM signals and overseas power)? What's the resolution of the video? Projectors that produce higher video resolutions produce sharper, cleaner images.

• New digital video systems are here, and many projectors now include component video inputs to allow direct connection to DVD players, plus digital TV tuners and VCRs when they are available. It's important to note that any projector, monitor or TV will be able to display digital TV signals. If you want to take advantage of the HDTV clarity, however, you'll need a higher-resolution video or computer projector, and a component input will help by reducing noise. (It works by dividing the chrominance portion of the video into red, green and blue segments.) For more information about digital TV, see our digital television tech tips.

• Aspect ratio is becoming important with digital TV formats as well, and it's important that your projector will display the aspect ratio of your source. Most computer and video images use a 4:3 ratio—that is, the ratio of the width of the image to its height is 4:3. But wide screen movies and HDTV formats use 16:9 and SXGA, while it will display on a 4:3 monitor, actually uses a 5:4 ratio.
  

• Lamp type. Most LCD projectors use a metal halide or UHP source, which offer a very white light and a useful life of 750 - 2,000 hours (depending on your projector model). They typically do not burn out suddenly, but gradually grow dimmer, giving you plenty of warning that it's time for a replacement.

• Contrast ratio, which measures the difference between the brightest white and darkest black your projector can produce, should be an important spec, but there seems to be a problem in how it's measured. We've done side by side comparisons between LCD projectors rated at 100:1 and 300:1 and found little or no difference in their images. We're now including contrast ratio in our catalog, but it's a good idea to take this spec with a grain of salt.

• The number of colors you need, while once important, is no longer an issue. All of the LCD and other projectors United handles offer 16.7 million colors.

Useful features
Beyond the basics, you'll want to consider whether your LCD or data projector includes:

• Intelligent resizing technology (also called "intelligent compression" and other names), maps high resolution computer images to a lower resolution LCD. This process works much better than plain "compression," showing the entire image at very acceptable sharpness. It works best going only one step up. Using an 800 x 600 projector you'll get very good 1024 x 768 images, but 1280 x 1024 will be noticeably fuzzy.

• A direct digital video input (when used with a computer with a digital video output), will increase the quality of your projected image by eliminating the need to convert a digital RGB signal to the analog RGB accepted by most projectors and monitors.

• A video line doubler (or scan doubler) increases the number of lines of vertical resolution from the 525-line standard to 1,050 lines. It does so by repeating each scan line, resulting in a sharper-looking picture. It's important to note that line doubling does not affect a projector's resolution spec, since resolution is usually specified in horizontal terms.
  

• A zoom lens. Useful if you can't control the exact placement of the projector.
  

• Keystone correction or lens shift corrects rectangular distortion caused positioning the projector away from the center axis of the screen. Adjustable keystone correction is a real plus, though nearly all projectors have at least a fixed correction factor which allows you to position it below the center of the screen.
  

• Motorized focus. Allows you to walk up to the screen and focus using the remote control (for best accuracy).
  

• Mouse control: operates your computer mouse from a wireless remote control. If your PC has a USB mouse connector, it will recognize a USB compatible mouse even if you plug it in after you've started up your computer.
  

• On-screen pointer also operates from the remote control. Laser versions are the easiest to see (and to use).
  

• Monitor loopthrough allows you to see your computer screen while the image is being projected.
  

• Multiple inputs allow you to switch between more than one computer or video source.
  

• Audio amplifier and speakers. Most projectors have a sound system, but the quality can vary (and the specifications you need to judge that quality are not normally available). Still, it's easy (and economical) enough to add a lightweight sound system for use with large groups, and if you do so, you'll have sound quality way beyond anything built into any projector.
  

Beyond the specifications
There are some comparisons that are very difficult to make from a spec sheet (and, at times, the measurements that specifications are based on aren't always made the same way). You'll really need to see the projector or panel demonstrated to form a judgment, especially for:

• Color accuracy. Besides the number of colors, how well does the the unit handle subtle color renditions, such as flesh tones? How clean are photos or video?
  

• Even illumination. Does the image have hot spots or a clean, even brightness from corner to corner? Is the focus consistent from center to corner?
  

• If it's an 1024 x 768 projector, how good are the 800 x 600 and video images? Do any resolution trade-offs work for you?
  

• Reliability. Will the projector work through a critical presentation? Does its manufacturer have a good reputation? Does it use a long-life lamp? What's the warranty? Is it UL listed?
  

• Serviceability. How long will you have to do without your projector if it breaks? Will your dealer stand behind you if you need it for a critical meeting?