HDTV Fundamentals

The ins and outs of HDTV

Not that long ago, TV was TV. There was one main technology (cathode-ray tube, or CRT) and one broadcasting format (480i). Now, however, there are five different types of TV and a number of different technologies. There are also lots and lots of different ways to format a TV signal. In fact, the Advanced Television Systems Committee (ATSC), which is the organization that created the digital broadcasting standards for the United States, allows 18 in all. Fortunately, there are only five that you really need to be concerned with:

• 480i Standard Definition (SD). To create an SD picture, 480 horizontal lines of image information are sent in an interlaced (that's what the "i" stands for) format. Each frame (or image) of an interlaced TV signal is actually made up of two fields, one consisting of the odd lines of the image and the other the even lines. The two fields are displayed one after the other by the TV at a speed that's so fast that the eye sees only one image. SD images have the familiar 4:3 aspect ratio.

• 480p Enhanced Definition (ED). Like standard definition, a 480p EDTV image is made up of 480 lines of information; however, they are displayed in a progressive format (hence the "p"), which means the entire frame is displayed at one time. While there is no more image information than in an SD picture, the image appears sharper and smoother because the artifacts caused by interlacing are eliminated.

• 720p HDTV. The lowest of the high-definition resolutions, a 720p image is made up of 1,280 pixels by 720 pixels displayed progressively. While other formats display more picture information, many critics say that at normal viewing distances, this format presents a picture that's just as appealing and even more film-like. Among major programmers, only ABC and its subsidiaries (including Disney Channel, ESPN and ESPN2) as well as Fox distribute content in 720p.

• 1080i HDTV. This format places 1,920 pixels by 1,080 pixels of picture information on the screen (in an interlaced format) for a vivid and sometimes breathtaking picture. Most broadcast, cable and satellite HD providers use this format.

• 1080p HDTV. This format takes the broadcast 1080i HDTV signal and presents it in a progressive (non-interlaced) format for the richest images of all. In addition, these sets can accept a 1080p image from a Blu-ray Disc or upconverting DVD player. All current sets that can display a 1,920-by-1,080-pixel image can do so in the progressive (1080p) format. Satellite providers (DirecTV and Dish Network) are providing some on-demand programming in 1080p, as are some streaming video providers, such as Vudu. However, because it takes up so much bandwidth, it is unlikely that any broadcaster will be distributing HD material in 1080p in the foreseeable future.

Note that while ATSC-compatible tuners must be able to receive all ATSC formats, the TVs themselves are free to take those signals and scale them to fit their native resolutions, which, for manufacturing reasons, don't always match up exactly with the ATSC standards. Regardless of the resolution, HDTV looks terrific compared with standard definition.

Simply buying an HDTV does not automatically mean you get HDTV images on your screen. The hardware is only one part of the equation. To get the high-definition programming signals, you need to subscribe to a digital high-definition cable or satellite service. Alternatively, you can receive HDTV broadcasts with an antenna, provided you are within range of a transmission tower. Of course, you won't get premium channels this way, but you can access the local affiliates of the major networks. AntennaWeb.org is a great website that lets you see what kind of over-the-air broadcasts are available in your area, as well as what kind of antenna you'll need to receive them.

With all TVs now required to have digital tuners, HD-ready sets (those that can display HD images but lack an integrated digital tuner) are all but gone from the market, with some notable exceptions. The law requiring new TVs to have a digital tuner does not apply to monitors -- those TVs that have no tuner at all. Tunerless monitors can be a good choice for those who get all of their TV from cable or satellite, but you'll need an external tuner to get any over-the-air programming. Most front-projection TVs also lack tuners of any kind.

Some HDTVs are compatible with CableCards. These TVs don't require a cable box to receive premium programming from cable companies. You plug the digital cable feed directly into the TV, and your cable company installs a CableCard (which goes into a slot on the TV). The CableCard unscrambles the channels to which you've subscribed. However, reactions to first-generation CableCards have been lukewarm, mostly because you can't use any of cable's interactive features. You can't order movies on demand with the remote or access the interactive programming guide.

Tru2way is a two-way standard for delivering scrambled programming and passing interactive content -- such as the program guide -- to compatible TVs without a cable box. Though there were initial signs that the technology would be widely embraced, and six major cable operators signed on, actual rollouts are well behind schedule, and few other cable companies have expressed interest. In addition, while Sony, Panasonic and Samsung are among set makers that have announced that they will support Tru2way, to date, only Panasonic has actually released Tru2way TVs.

Cable subscribers might also be interested in sets with QAM-compatible digital tuners. QAM, which stands for quadrature amplitude modulation, is the transmission scheme cable companies use to distribute digital TV signals. A QAM tuner can allow you to receive any unscrambled, basic programming you subscribe to without a cable box or CableCard, so that's one less piece of hardware you'd need. An external box or a CableCard is still required for premium programming, however.

There are four main types of HDTV display technology. Plasma and LCD TVs draw lots of attention, as these two types are wall-mountable. LCD flat panels come in smaller, less-expensive sizes, while plasma TVs are only available in 42-inch and larger screen sizes. Rear-projection TVs aren't as big as the behemoths of a few years ago, but that hasn't stopped them from being driven to near extinction. As of now, just one maker -- Mitsubishi -- continues to produce these sets. Front projectors are very much alive, on the other hand, though their requirements don't make them the best -- or even an acceptable choice -- in many situations. However, prices are way down, and front projectors still deliver the biggest screen sizes available regardless of technology. Some conventional tube-based TVs are still available. However, all are standard-definition sets.