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Your HDTV: Projecting a Good Image

When most people think of HDTV, they think of big screens — specifically, projection TV systems. Projection TVs offer the most bang for the buck in the HDTV world (and in the TV world in general) — the biggest screen for the fewest bucks.

Rear-projection design

Most projection HDTVs sold today are rear-projection TVs (RPTVs). The biggest advantage of the RPTV (compared to front-projection systems) is simplicity — all the pieces and parts are in one chassis, just as they are in an old-fashioned CRT (tube) TV. So with an RPTV, there's no lens adjusting and focusing of the picture on the screen.

RPTVs can have extraordinary picture quality. The biggest factor, when it comes to picture quality, isn't so much RPTV-versus-front-projector as it is the type of projection system — and the quality of the individual projector.

The biggest picture shortcoming with most RPTVs revolves around the viewing angle of the RPTV — this describes how far from perpendicular to the screen a viewer can be and still see the picture clearly. Some RPTVs have poor viewing angles, so they're less than best when viewers are seated far to either side of the HDTV

The newest RPTVs, which use microdisplay technologies such as DLP, are actually quite slim — barely thicker than flat-panel TVs such as plasmas. These microdisplay RPTVs are perhaps the best buy in HDTVs, combining a large screen with a slim overall package, and a picture as good as plasma at less than half the price.

Projection TV systems

When you're evaluating projection TV systems, you must choose a projection technology. There are two types of projection systems:

  • Traditional projectors based on CRT (cathode ray tube) projectors. These CRTs are specialized versions of the same tubes found in traditional TVs to generate the light projected onto the screen.
  • Microdisplay projectors. These use microelectronic systems such as LCDs and DLP chips, in conjunction with a powerful light bulb, to project images on the screen.

Generally speaking, CRT-based systems create the best-looking picture, but they do this at the expense of ease of use, size, and overall brightness. Microdisplay projectors trade off a little bit in ultimate picture quality, but gain in ease of use, brightness and compactness.

CRT

The granddaddy of projection TV systems is the CRT projection TV. The CRT tubes in these projection TVs are similar to those used in direct-view tube televisions (these are the regular old TVs), but with one major difference: while a direct view HDTV has a single tube, a projection CRT HDTV has three tubes, one each for red, green and blue colors.

Tubes have some definite picture advantages over other systems, as well as some additional negatives. For example:

  • Pro: best black-level reproduction. Blacks are essential when you're watching a scene on TV with dark (or no) lighting and lots of shadows. CRTs are the best of all systems at reproducing black colors on screen.
  • Pro: excellent color reproduction. Many microdisplay systems have a particular color that they can't reproduce as well as others — CRT systems don't usually face this issue.
  • Con: reduced brightness. Compared to microdisplays (which use an intensely bright bulb to create light on the screen), CRTs put out fewer lumens.
  • Con: susceptible to burn-in. CRTs create a picture when electrons hit a layer of phosphor (which lights up when struck by these electrons). Images that don't move (such as those in video games or even stock tickers) can create a permanent "ghost" image in these phosphors — effectively ruining your screen. CRT projection TVs are the most susceptible HDTV for burn-in.

LCD

LCDs range in size from tiny, sub-1-inch models to huge 40-plus-inch versions. LCD projection TVs tend to use LCDs from the smaller end of this continuum, often as small as 1 inch or less. Like CRT RPTVs, LCD RPTVs use not one, but three image sources — an individual LCD each for red, green and blue. Unlike CRTs, however, these LCDs don't require periodic alignment (convergence), which makes owning an LCD RPTV a much easier task for those of us who don't specialize in TV maintenance.

The small size of these LCDs is the biggest advantage of the LCD RPTV when compared to a CRT model — LCD models are simply much thinner, closer to a flat-panel TV than a traditional RPTV in depth. So they can fit into your tight family room better than an older-tech CRT TV.

There are a few disadvantages of LCD projectors, however, including the following:

  • Screen doors: LCD screens consist of a large number of sharply defined, square-shaped pixels that make up the image. When blown up to big-screen size (50 inches or greater), these pixels can become visible. You'll notice this when you feel like you're looking out your home's screen door. Better LCD HDTVs avoid this syndrome, but it can show up on even the best projectors for very large images.
  • Dead pixels: This is a huge deal for some folks — others won't even notice it. There are literally millions of pixels between the three LCDs found in an LCD-projection HDTV. Occasionally one of these pixels malfunctions or becomes "stuck," resulting in a visible dark or bright spot on your HDTV's screen. The real problem is that many manufacturers won't fix or replace your HDTV if you only have a few of these malfunctioning pixels — so if this sort of thing really drives you crazy, check out the warranty terms before you buy!

DLP

Digital light processing (or DLP) systems are based on micromirror technology — a DLP chip (the basis of the projector) is an optical semiconductor with millions of tiny mirrors controlled by the logic portion of the chip. With a DLP, color is added with a separate device known as the color wheel — a set of red, green and blue filters arranged in a wheel that is located in the path of light reflecting off the mirrors in the DLP chip — these three colors mixed together produce the colors found in your HDTV's source material.

DLP-projection TVs are very thin (some less than 6 or 7 inches — nearly in plasma territory), produce a bright, beautiful picture, with better than LCD black reproduction, and excellent color reproduction.

When you're choosing a DLP-based projection system, be sure to read the fine print. Not all DLP systems are HDTVs — some inexpensive projectors (mainly front-projection systems) use older DLP chips that don't reach HDTV resolutions. The latest DLP chip (at the time this article was written) is the HD2+, which provides 1,280-by-720 resolution (this perfectly matches 720p resolution requirements).

Most people don't notice a situation with DLPs called the rainbow effect. This is caused by the spinning color wheel, and can cause a very small percentage of the population to feel dizzy, or get a headache, while watching DLP — particularly when moving their heads, or during rapidly moving scenes on-screen.

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