High-definition TV is probably confusing to most folks, so I’m going to lay out the basics in the interest of world peace and harmony and explain the technologies currently duking it out for your consumer dollar.
First, lets understand that high-definition TV is digital, but not all digital TV is hi-def. DVDs, for example, are digital, but they don’t qualify as hi-def because there’s no more detail in the DVD picture than in a good standard def, analog TV image. Digital TV programming can take any of several formats, defined by their image geometry and the frequency with which the picture is updated. The high end of the scale of these formats is hi-def, the low end is standard def, and the middle is called Enhanced Definition TV or EDTV. Nobody is currently broadcasting in the best format, an image geometry of 1920 pixels x 1080 lines, progressive scanned at 30 frames/sec. The popular formats are 1280 x 720p and 1920 x 1080 interlaced. “Interlaced” means that the video picture is formed out of pairs of images, one consisting of the odd-numbered lines and the other with the even-numbered one; this is a trick that fools the eye and uses only half as many bits as progressive scan. Digital TV at 480 lines progressive is EDTV, and 480 interlaced is standard def, SDTV, the format used by DVDs.
Size and Shape
Hi-Def TV monitors are generally larger and wider than Old-Timey TV (OTTV). The screen shape has a ratio of 16:9 (width:height) compared to 4:3 for OTTV. This is handy when you’re watching movies, but for normal TV programming it means you’re going to have black bars on the left and right sides of your picture. So if you’re used to watching a 27″ set, you would need to get at least a 34″ widescreen HDTV to see an image of the height you’re used to (17″) when you’re watching shows that aren’t tailored for the wide screen.
The main advantage of HDTV is its ability to fill large screens with crisp images that aren’t grainy or otherwise funky-looking, so if you don’t get at least a somewhat larger screen than the normal OTTV screen you’re kind of missing the point.
Geometry
When you’re looking for an HDTV monitor, bear in mind that very few of them are capable of displaying the largest formats directly, pixel-for-pixel; that is, they’re all capable of receiving 720p and 1080i, but they typically do some image processing to display the images on a screen that has somewhat different geometry. For example, most HDTV plasma panels have a native resolution of 1024 x 768, just like crappy computer monitors. But they have image processing capability that allows them to “scale” 1280 x 720 or 1920 x 1080 images onto their native geometry. Since the image changes 30 or 60 times a second, and there may not be a whole lot of difference between any two adjacent pixels, these panels produce fine images up to a certain size, depending on how demanding you are, and are better looking than regular TV in any event. But you’re still going to be better off with a display whose native geometry is perfectly matched to HDTV formats, or one that has flexible geometry like an old-fashioned picture tube, because you’ll avoid weird image processing defects that plague all but the most expensive of plasma sets. That being said, this WalMart wonder is a nice TV set, and nobody knows TV like WalMart shoppers.
The alternative display technologies are LCD (just like computer displays) and a couple of variations on LCD for projection TV, DLP and LCoS.
LCD
Like plasma, LCD is a direct-view, panel technology that produces screens four or five inches thick that you can hang on a wall like paintings. LCD can be had in HDTV geometries, but some of it uses computer geometries as plasma does, so you should read the fine print. As with all of this stuff, you can pay nearly as much or as little as you want for an LCD HDTV, as these two examples show: BenQ has a 37″ monitor with native resolution of 1920 x 1080 (just what you want) for $2000 at Crutchfield. And Sharp has some smaller 32″ sets for twice as much.
DLP
Digital Light Processing is a nice, fairly inexpensive projection technology that’s used in medium-sized rear-projection TVs (typically from 46″ to 60″). DLPs use a chipset from Texas Instruments with 1280 x 720p, so these sets do have to scale 1080i down, but it’s pretty straightforward exercise as each 4 lines of input produce 3 lines of output. DLP TV have a single gun, and get the three colors that TV pictures are made from by shooting it through a “color wheel” that spins at 10,000 RPM or so. It’s a clunky process, but the images are acceptable. This Toshiba is a good example of a DLP set.
LCoS
Liquid Crystal on Silicon is a brilliant concept that JVC developed for video editing systems and has recently adapted for home entertainment, and it’s my bet as the winning technology in this area as it’s both cheaper and brighter than either LCD or DLP. The trick behind LCoS is that the beam of light that shines through a liquid crystal in LCD or DLP bounces off the LCoS crystal, which gives the colored light more intensity. These sets also use three guns so you don’t have a clunky color wheel, and the geometry is HDTV-oriented and not a carry-over from computers. JVC makes the best LCoS sets, but you can also get them from Philips and others, and the prices are reasonable.
CRT
OK, we’ve covered all the new technologies, but what about good, old-fashioned CRTs? It turns out they have a couple of natural advantages over the fixed-pixel-arrays that we’ve mentioned, flexibility and cost. CRTs form images by shooting an electron beam on a phosphor coating inside the tube, using electromagnets to direct the beam, which sweeps the screen from top left to bottom right 30 times a second, more or less (29.97, actually) . They can adjust resolution by altering the speed that the beam travels and by changing the number of times it turns on and off to form picture elements (pixels). It’s not really as flexible as all this at the high end, where a shadow mask is placed in between the beam source and the phosphor to sharpen the dots, but the general principle still applies. And CRTs are cheap to make because we’ve been making them for so long. The LCD companies are having to build brand-new and very expensive factories to produce the larger panels they need at a low cost, and somebody has to pay for them. Sharp is building their own, LG and Philips are collaborating, Sony and Samsung are collaborating, and the Chinese Army is building one with slave labor.
The down sides of CRT are size – they top out at 34″ – and the weight, about 200 pounds for a 34″. Old projection TVs also used CRT guns, but that’s a downer. Good sources for HDTV CRTs are Toshiba and Sony.
OK, that’s that for displays, there’s a lot to be said about HDTV recorders and programming, but that’s for another post.