Sunday, June 12, 2005

Picking an HDTV

In order to watch HDTV, you have (surprise, surprise) to possess an HDTV. (You also have to have at least one HD signal source ... but that's a topic for another time.) What kind of HDTV should you get?

As far as I'm concerned, your HDTV needs to have a widescreen aspect ratio, expressed numerically as 16:9 or 1.78:1. There are some so-called HDTVs that have a squarish 4:3 screen, like in the old days. When they receive a 16:9 program, they put black bars above/below the image. Many do so without losing vertical resolution, thanks to a clever signal-processing trick. But the image's frame is still scrunched, relative to the full height of the screen. Who needs that?

To be a true HDTV, your unit must be able to display either 1080i or 720p (or both). 1080i puts 1,920 pixels across the frame and 1,080 up and down. The odd-numbered pixel rows of each frame arrive in the first 1/30 second, the even-numbered rows in the next. This is what is meant by "interlaced scanning," the "i" in 1080i.

720p frames are 1,280 pixels across by 720 up and down. All pixels are refreshed at once, every 1/60 second. This is "progressive scan," the "p" in 720p.

Not all true HDTVs can cope with the full 1,920-pixel horizontal resolution of 1080i (but all can at least render all 1,280 pixels in each 720p line). When 1080i is being displayed, the set's lesser native horizontal resolution may reduce the amount of detail present in the image somewhat. That slight reduction is not usually considered a major defect.

Any so-called digital TV that cannot give the full resolution of 720p, but which has more than standard-def resolution, is an "extended definition television," or EDTV. EDTVs give a nice picture, but they're not true HD.

All true HDTVs, like EDTVs, have some way of inputting, as well as displaying, 1080i/720p signals. Those that are "HDTV monitors" or "HD-ready TVs" can't receive HDTV over-the-air broadcasts without an external settop box and antenna. Those that are marketed as HDTVs per se, without any further qualification, or those that say "HD built-in," can.

All HDTVs and HDTV monitors can receive 108oi and/or 720p signals from outboard gear like cable-TV boxes and satellite receivers — plus, a lot of DVD players now upconvert their outputs to 720p or 1080i.

These hi-def signals coming into the HDTV from external gear can be analog or digital. If analog, they will typically come in over three-headed "component video" cables. If digital, DVI and/or HDMI connections will frequently be used. Either of those digital connections should be capable of honoring HDCP copyright protection, or the HDTV might not be compatible with cerain external gear.

That's basically it. Any TV made for the U.S. market which complies with those criteria is an HDTV. But which one should you buy?

There is, of course, no quick answer.

First off, you have to choose from four basic flavors: the flat panel, the rear projector, the front projector, and the direct-view TV. Of these, the last is the most familiar. A direct-view HDTV uses (gasp!) a "picture tube": a cathode ray tube or CRT. On the face of this tube appears a full-color picture ... sound familiar? It's just that the picture has a lot more detail (and is wider) than ever before.

A flat-panel TV is just that: a thin, attractive, light-producing slab, usually an LCD (liquid crystal display) or a plasma panel.

A front projector makes an image and throws it out onto a distant external screen, just like in movie theaters, enlarging it as it is projected. LCD and CRT technology are often in use here ... one tiny LCD panel or three separate picture tubes, red, green, and blue. Other technologies used for front projectors include DLP (digital light processing) chips. A front projector is the option of choice for the true "home theater."

A rear projector is just like a front projector except the screen is housed within the TV itself and is translucent. The picture is again produced by LCD, tri-CRT, or DLP technology, or something similar. With tri-CRT technology, the image is optically thrown onto the back of the translucent screen from three modest-sized cathode ray tubes, one red, one green, and one blue, inside the set. LCD and DLP rear projectors replace the three tubes with a single tiny digital image producer — or, in the case of very expensive DLPs, three separate "micromirror devices," one for each primary color.

Any of the technologies used in flat-panel, rear-projector, or front-projector displays — with the exception of the venerable CRT, that is — is a "fixed-pixel" technology. The image is made of tiny discrete sources of light — in DLP, they're actually individual micromirrors — not by an electron beam sweeping across a phosphorescent coating. Each fixed-pixel display has a fixed number of these light sources — which constitute the pixels themselves — lined up in the horizontal direction, and also in the vertical. These two numbers are the limiting factors on how hi-def the displays can be.

When it comes to CRTs, the upper resolution limits are not as easy to know. (I'll leave it at that.) No direct-view CRTs can produce all the fine detail of 1920x1080i, but some (ultra-pricey) front- and rear-projectors can. Many aficionados think CRTs give the best, smoothest, most natural video renditions, with the most accurate colors, the deepest blacks, and the greatest amount of shadow detail.

So, again, how do you pick an HDTV? Once you know which basic type you want, you can use Viewing Angle Calculator and/or Viewing Distance Calculator to figure out how big an HDTV you need, based in part on your expected viewing distance and desired viewing angle.

Once you've reached this point in your deliberations, however, you may find you need to revise your thinking. For instance, if you decide you want a TV over 45" in diagonal measure, that pretty much lets out flat-panel LCDs, which may otherwise have been your first choice. Anything over about 34" will eliminate direct-view CRTs. And if you just want a modest-sized HD display for the kitchen counter, plasmas are decidedly too big.

Rear- and front-projectors as well as plasmas, on the other hand, can give you pictures that are pretty darn big ... for a price. The price is apt to be fairly reasonable for big-screen, CRT-based rear projectors and much steeper for all other truly large-screen displays and projectors.

You also need to make sure you physically have room for what you hanker to buy ... and all its outboard gear. This is generally a major problem only with the two types of projectors, front and rear. Direct-view CRTs are usually not all that big. Flat panels are quite space-efficient, even in the larger screen sizes, and can be mounted on a wall.

Rear projectors typically require a lot of depth clearance and a lot of height clearance. Those that are CRT-based usually house their three CRTs in the base, which means they take up a lot of space below the screen where you cannot put other gear. Non-CRT RPTVs are, on the other hand, getting thinner and thinner, and they usually sit tamely on a shelf above other gear.

Front projectors are a special case. They pretty much require a full-fledged home theater arrangement, in a dedicated room. The projector mounts on the ceiling, or at the back wall, or behind the (translucent) screen ... or sometimes it just sits on a raised table in the middle of the theater area. The other connected A/V gear is stashed elsewhere, often out of sight. The seats are positioned in front of the screen at an ideal distance from the projected image. The room is darkened for viewing, which means no exposed windows — and the result often outshines the local cineplex.

All that said, once again, how do you pick an HDTV? One way is to do a lot of research, read a lot of equipment reports and reviews. You can find a treasure trove of links to equipment reviews listed online at the website. Lots of valuable online home-electronics reviews can be found at c|net.

You also need to devour the enthusiast magazines such as Sound & Vision, The Perfect Vision, Widescreen Review, and Home Theater.

You need to visit Circuit City, Best Buy, Tweeter, and so forth — the actual bricks-and-mortar stores. But take any technical information you get there with a grain of salt. On the other hand, you can trust your eyes a little more. If a display looks particularly good, investigate it. (But remember, displays that look good under intense store lighting may not look good at home. Then again, those that seem weak in the store may be superior at home under more restrained lighting conditions.)

Then there are the online forums, two of the best being the AVS Forum and the Home Theater Forum.

Also, pay attention to your friends' HDTVs. What kind(s) do they have? How do they like them? How do you like them? What strengths/weaknesses most impress/bother you?

Happy hunting!

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