About HDTV TELEVISIONS
First of all the actual term for the new digital television standard is DTV. HDTV (high definition television) is really just a subset of a multitude of digital television signal formats that have been approved by the FCC for broadcast. Most home theater enthusiasts, however, are most excited by the few high resolution formats, for obvious reasons.
The three main types of DTV
Although the FCC has permitted broadcasters to transmit in a number of different video formats, the marketplace (i.e. broadcast community) has boiled down the options to just three.
1080I - Most broadcasters and other program providers have adopted the 1080i (interlaced) high-definition format, where each video frame contains 1,080 "active" horizontal scan lines displayed in two alternating fields of 540 lines each. Standard NTSC video also uses this interlacing technique, but has only 480 active scan lines per frame -less than half as many as in 1080i HDTV.
720P - The other high-definition format in use, 720p (progressive-scan), has 720 scan lines presented sequentially in a single frame, and offers picture quality approximately as good as 1080i. That's because while the total number of active scan lines is lower, more of them are on the screen at any given moment. So far, only ABC-owned stations are broadcasting this format.
480I/P - At the low end of the DTV hierarchy are picture formats whose resolution is about the same as good NTSC broadcasts or DVDs. Often referred to as SDTV (standard definition television), 480i and 480p both offer images in either a standard 4:3 or a widescreen 16:9 aspect ratio. In principle, 480p should look better than 480i, because it removes the artifacts of interlacing scan fields.
The major types of DTV displays
A direct-view set is the kind of TV where the screen is the front of a large glass cathode-ray tube (CRT). This venerable technology holds its own nicely with newer technologies because of its maturity. Engineers have been working on CRT design for almost 100 years, and the effort shows. Good direct-view sets can deliver very sharp, clean pictures with excellent brightness and contrast. Just about every other video display technology is still playing catch-up to CRTs in one performance characteristic or another.
The only serious limitation of direct-view sets is screen size. There are limits to how big a CRT can be without becoming too fragile, and the larger sets generally range in size from 32 to 40 inches (diagonally). In the past, direct-view tubes had slightly curved front ends, but the tubes used in many of the new HDTV models are flat right to the edges of the screen now. This helps eliminate glare from lamps and undraped windows and reduces geometric distortion around the edges of the image. The prices for direct view DTV televisions range from less than $2000 to more than $4000.
For sizes larger than 40", rear screen projection TVs, or RPTVs , use three small CRTs to project the red, green, and blue color components of a video image onto a internal mirror. This mirror than reflects the image onto a specially designed "lenticular-fresnel" screen mounted on the front of the set. RPTVs can be much larger than direct-view sets with high-end units offering up to 80" diagonal images. The larger models do take up lots of floor space -be prepared for that- but some of the smaller ones will fit in an A/V cabinet or even on top of a table.
On the whole, RPTVs deliver more detailed and dramatic HDTV images than direct-view models, particularly larger sets that use 9-inch CRTs instead of the more common (and less expensive) 7-inch tubes. But before settling on an RPTV, you should take into account that most of the programs you'll be watching for the next few years are likely to be in standard NTSC , so the RPTV edge may not be immediately evident. On the other hand, virtually all HDTVs incorporate circuitry that multiplies the number of NTSC scan lines, thus increasing its apparent resolution.
Flat panel plasma displays are the latest display technology in town and the best way to achieve larger video displays with uncompromised image quality. Plasma panels consist of an array of cells, known as pixels corresponding to the colors red, green, and blue. Gas in the plasma state is used to react with phosphors to produce colored light. Interestingly, these phosphors are the same types used in cathode ray tube (CRT) devices such as televisions and standard computer monitors.
With flat panel plasma screens, in addition to bright, crisp images, there are other advantages. Unlike RPTV projection screens, which are designed to concentrate reflection to a narrow viewing area for brightness, plasma screens permit an exceptionally broad viewing angle -over 160 degrees. This means that no matter where audience members are in the room, the brightness and clarity are brilliant.
When you are ready for a true theater experience in your home, you're ready for a front-projection system. It's called a front projector because it's a two-piece system that literally projects the image across the room onto a screen. This setup requires that the room be completely darkened - any light will wash out the image. Front projectors are capable of the largest home images - 80 to 110 inches or larger, depending on the capabilities of the projector. We will talk more about front projection televisions in just a little while.
Let’s get wide
Regular TVs have what's called a 4:3 aspect ratio (pronounced "4 by 3"), which means that if a television screen is three inches high, it's four inches wide. The HDTV standard calls for widescreen 16:9 images which means they are wider than 4:3 images for a given screen height. Nothing gets left out when you view a movie in widescreen format. If you've ever seen the message, "this movie has been formatted to fit your TV screen," you know what it's like to watch a wide-screen movie on a standard TV screen. You are only seeing part of the whole picture.
Since manufacturers make HDTV sets in both standard 4:3 and widescreen 16:9 aspect ratios, you need to consider what kinds of programs you like to watch, and will be watching in the future, before deciding which to buy. With standard programming, a widescreen TV has to either stretch the image to fill the screen or position it in the center, flanked by black or gray bars. Conversely, most sets with a standard 4:3 screen show HDTV images in a letterboxed format, with black bars at the top and bottom of the screen. Letterboxing does give you the benefit of widescreen presentation by displaying uncropped, correctly proportioned images, but the visual impact is diminished because the full screen area isn't being used to deliver picture information.
If you are looking to purchase a DTV direct view TV, you should know that 16:9 models are a lot more expensive than 4:3 ones. This is because a 16:9 CRT costs quite a bit more to produce than a 4:3 picture tube. You also should consider that while a 16:9 screen is wider than a traditional TV's, it's shorter as well. In fact, a (diagonally measured) 34-inch 16:9 screen is about the same height as a conventional 27-incher! If you want a 16:9 display, make sure you'll be satisfied with the overall size of the picture before you buy a direct-view model.
Give me lots of input
You want to make sure your new home theater TV has all the inputs you will need. At the vary least look for:
One or two RF inputs (for antenna and cable feeds) plus a composite-video input. Composite video is a combination of NTSC picture (all the color, luminance, and synchronization information) and its accompanying audio signal. Another must is S-video, which conveys the luminance (brightness) and chrominance (color) portions of a video signal separately. With sources in which these elements aren't combined into one signal to begin with, such as a DVD, S-video will usually give you a much better picture by eliminating the artifacts that occur when a composite signal is decoded.
Component video takes this process a small step further by keeping separate the two color-difference signals that make up the chrominance portion of an S-video signal. The digital video signals of DVD, DTV, satellite TV, and digital cable are MPEG-2-encoded component video. With these sources, a component connection eliminates still another stage of processing inside the TV set. In terms of image quality, the step from S-video to component video is less noticeable than that from composite- to S-video, but it can still make a noticeable difference on some sets.
Two basic flavors of component-video input are found on most sets. The first is designed to accept 480i signals from DVD players with component-video outputs and is found on analog TVs and a few EDTV and HDTV sets. The second is called a wideband component video input, and it can also handle 480p signals from DVD players with progressive-scan outputs and high-definition signals from HDTV tuners.
If you use a camcorder, you will find it very convenient to have front panel video inputs available on at least one component in your system. Many VCRs and home theater receivers have these inputs already. If yours don’t, you might want to make sure your new DTV TV does.
You may also come across RGB+H/V and VGA inputs. The former requires five jacks — three for the components of an RGB signal and two more for the accompanying horizontal and vertical sync signals. This type of input is much more common on high-end front projectors than on direct-view sets. VGA inputs — essentially just another way of conveying an RGB signal — use 15-pin jacks designed to mate with computers and some HDTV tuners.
Comb Filters
Because of the way the NTSC television system entangles chrominance and luminance in the composite-video signal, they aren't easy to pull apart cleanly without sacrificing resolution. What happens is that these carriers can interfere with one another, causing picture anomalies such as dot crawl and color bleeding. To counteract this, color TVs have comb filters, which work to stabilize and sharpen the video image.
Simple two-line analog comb filters handle the job in decent fashion but not flawlessly. These are uncommon in DTV sets. They sometimes produce obvious artifacts, such as dots crawling along sharp edges in a color picture. More sophisticated comb filters convert the analog video to digital and attack it via signal processing.
Until recently, almost all the digital comb filters worked with just three scan lines of information at a time. Although three-line digital combs are better than their two-line analog predecessors, their performance pales against that of the latest 3-D digital comb filters, which work with entire frames of information at once. This is the most efficient of all comb filters, and virtually eliminates dot crawl and color bleeding. You will get the best color TV picture possible.
More about Front Projection TVs
Actually, unlike most direct-view or RPTVs, front projectors are not actually TVs - they don't have TV tuners for dialing in stations. Like most RPTVs, front CRT projectors use three CRTs to create video images. Seven-inch CRTs are the norm in most projectors, but 8- and 9-inch CRTs are available on higher-end models. Although they are expensive, the larger tubed models can produce higher light output, sharper focus, and richer colors.
CRT projectors required some special care and feeding, though. Besides requiring a completely darkened room, CRT front projection systems are the British sports cars of the TV world - they require unique care and maintenance. For example, during the installation process, it might be a good idea to leave the calibration and alignment process to a qualified technician.
The screen that CRT projectors display on is an important part of the equation, equally important as the projector itself. The biggest obstacle to creating big pictures is light output, and screens must maximize the light coming from the projector. They accomplish this with high-tech fabrics and surfaces that have variable amounts of gain. You do have to be careful when you select a screen that you buy an appropriate size and gain or you could be compromising the video image that you have paid so dearly to obtain.
LCD (Liquid Crystal Display) and DLP (Digital Light Projection) systems are a different way to project video images and thus can offer a significant cost savings over CRT systems. Unfortunately, LCD was (and still is on some models ) visually inferior to tubes, primarily in the ability to generate deep blacks in the image. The newer DLP projectors don’t suffer as much from this black level problem; this is mainly due to trial and error improvement made in DMD (Digital Micro Mirror) chips over the last several generations.
"Native resolution" is a significant issue with LCD / DLP technology. CRT tubes usually don’t have native resolution problems. A LCD / DLP projector only has one resolution and must digitally change any input signal to ‘best’ match the LCD / DLP screen. Not all projectors are equal at doing this and may produce "soft" looking images. As stated before, tube base projectors usually don’t suffer from resolution scaling visual problems. The scanning frequencies used to drive the tubes vertical and horizontal deflection circuits can be adjusted to match most any input signal. CRT projectors do have a maximum scan / resolution limit on what signals they can adapt to but most today cover the entire range of DTV signals.
Bulb life is sometimes forgotten when a front projector cost analysis is made. Many of the good HDTV capable LCD / DLP projectors have bulbs that burn for 1000-2000 hours and cost several hundred dollars a bulb . This hidden cost should be factored into your decision.
Built-In vs. Outboard Tuners
Maybe the most important decision you'll have to make is whether to buy an all-in-one HDTV, which has a built-in tuner to receive both over-the-air digital broadcasts and standard transmissions, or an HDTV monitor, which requires an external HDTV tuner to receive high-def broadcasts. (Most HDTV monitors do include an NTSC tuner to receive analog broadcast and cable signals, however.)
At this stage, buying an HDTV monitor may be the way to go. You'll save some money in the short term, and you can always add an HDTV tuner later when more digital broadcasts are available. And you won't be left out in the cold if the high-def standards for cable turn out to be incompatible with current tuners, which seems likely.
TV Audio
If you plan on using your home theater receiver and speakers to process and deliver your video sound, and virtually every home theater owner does, your TV's audio quality may not be a critical factor. However, if you or somebody in your family occasionally likes to simply turn on the TV and surf, it might be a good idea to choose a TV with a good sound system.
All of the 27" and larger TVs most have MTS (Multi-channel Television Sound) stereo. Look for powerful audio amplifiers (5 watts or more). The higher the power output, the cleaner and more realistic the sound is. If you are buying a TV as a stand-alone component, you'll enjoy the improved sound you get with higher power.
Picture-in-Picture (PIP)
The ability to inset a small picture from another channel or source into the main picture you're watching and to swap back and forth between them is now almost a standard feature on all but very low-end sets. There are two types of PIP: one-tuner and two-tuner. Sets with one-tuner PIP contain only a single TV tuner and therefore rely on an external source, such as a VCR, to supply the second picture. More convenient is two-tuner PIP, which uses a second tuner in the TV itself. This feature is built into many of the RPTVs currently offered.
Remote Controls and More
As the number of features built into TV sets multiplies, the design of the remote control becomes increasingly significant. Basic remotes operate only the TV, but high-end sets often come with "universal" or "learning" remotes that can also control at least some functions of other components. Such multicomponent remotes are a good idea up to a point, but as a remote takes on more functions it tends to become more cluttered and confusing to use.
Many home theater owners don’t take this "supplied remote" issue very seriusly because they intend on buying some of the programmable touch screen remotes that are now available. This kind of remote is quite capable of running all but the most complex home theater systems. The Philips Pronto is good example of this.
