Giz Explains: The Ultimate HDTV Cheat Sheet

It's truly the best time of year to buy an HDTV, and well, here's every confusing TV term you might encounter, explained in one place.

Resolution aka 720p vs. 1080i vs. 1080p Resolution is pretty simple—it's the number of individual dots (pixels) that make up a display, arranged in a grid. However, when it comes to TVs, we tend talk about it in a slightly weird way, as lines of resolution (think of a FourSquare board), and we tend to do it in shorthand. So, for instance, a standard definition set has a resolution of 640 x 480, which refers to 640 vertical lines, and 480 horizontal lines, of resolution. A 720p TV has 720 horizontal lines of resolution, and most typically 1280 horizontal ones. A 1080i or 1080p TV is 1920 x 1080. And the whole 1080i vs. 1080p thing—i stands for interlaced, where only every other line of resolution is displayed, while p is for progressive scan, where the whole picture's displayed at once. Really, since even the cheapest sets are progressive now, you don't have to worry about it.

An important thing to consider, however, is the Lechner Distance, or the distance at which your eye can actually process all of the detail in a 1080i/p resolution image. While you should consult the chart, basically, if you're sitting further back than 2 metres from a 52-inch TV, your eyeballs can't actually resolve the difference between 720p and 1080p, so you might as well save the cash.

Motion Resolution A somewhat trickier spec that some TV experts swear by, it refers to how well a set's resolution holds up when stuff's actually moving on the screen, like a baseball player running down a field. Plasmas tend to have better native motion resolution than LCD, but LCD has been fixing this problem. (See "hertz," below.)

Viewing Angle Basically, it's how far to each side of the TV you can be and still see the picture, measured in an angle that is, naturally, less than 180º. Again, traditionally this was more of an LCD problem than a plasma one, but all TV technologies have had some issues in the past, and the worst offenders used to be DLP and other microdisplays.

To see viewing angle at work, start where the picture on a TV looks best, and move to one side—now note where the picture starts looking weird, with the colours changing, washing out and getting hard to see. Nicer sets reach nearly 180º, so plenty of people can take part in the HD glory.

Hertz, or What 120Hz and 240Hz Mean Hertz is basically just the number of times the image onscreen refreshes a second. Because of broadcast standards, TVs in the US need to be 60Hz, meaning they refresh the image onscreen 60 times a second. (In Europe, the standard is 50Hz.) Video sources are generally 30 or 60 frames per second, because of this, and a regular video camera shoots at 60fps a second. So typically, 60Hz sets are the norm.

Lately, though you have 120Hz, and even 240Hz sets, all of them LCDs. They do this to increase motion resolution—see above. A 120Hz TV refreshes 120 times a second, and it comes up with those extra frames by making them up—either duping the frames that are there and putting black spaces in between, or by splicing in intermediary frames that are basically realtime morphs of the two frames they come between. Stuff looks really smooth—sometimes too smooth, true—but the point's to fight LCD's motion blur disadvantage against plasma.

240Hz is another ball of sticky still, promising less motion blur, but with a tradeoff. but there are two different ways to achieve it. One way's kind of cheating, in that it's a 120Hz that uses a flashing backlight to simulate 240 frames a second. The other, more "legit" 240Hz is genuinely faster, with images staying up on the screen for just 4ms before moving to the next. There's no real way to tell which kind of 240Hz a TV uses (though a "scanning backlight" is a tip off it's not the "real" 240Hz). There is a law of diminishing returns in reducing motion blur as you climb past 240Hz, but for some serious AV nerds, like Home Entertainment's Geoff Morrison, it does make LCD TVs more watchable.

AU: In Australia, we have 100Hz and 200Hz instead of 120 and 240, thanks to the wonders of the PAL broadcasting standard.

Plasma TV brands sometimes boast "600Hz," but that's mostly to show off to LCD shoppers that these kinds of motion-blur refresh problems are really specific to LCD. It's not so much a spec as a declaration of the tech's superiority in this department.

To make things just a tad weirder for you, films have been shot since ancient times at 24 frames per second, so many TVs have a 24P mode, meaning the screen refreshes 24 frames per second, or in multiples thereof. (Any mathmagician can tell you that both 120 and 240 are divisible by 24.)

Plasma The basic way plasmas work is that there's a party of noble gases trapped between two glass panels that are zapped and light up all pretty. More practically, what plasmas offer over LCDs is superior colour (often), better motion (typically) and deeper blacks (always and forever, with a couple of exceptions). The tradeoff is that they're more power hungry, and generally heavier.

The life-or-death questions people have about plasmas are almost mythical now: Burn-in, where an image is permanently etched into the panel after being left up on screen too long isn't really problem anymore (unless you're sadistic to your TV). The "Denver problem," where high altitudes affect sets, is less of an issue, but it exists: If you live at 6,000 feet or higher, you should read this summary by our friend David Katzmaier at CNet. Panel half-life is a very long time, now, about the same as LCD's backlight (which, of course, could be replaced, but we're talking like 10 year out). When it comes to the cheapest TVs, 720p plasmas are hands-down the safest bet for best picture quality.

LCD The people's HDTV technology, LCD, stands for liquid crystal display. The liquid crystal part is a gel that sits in front of a backlight, which is divided up into pixels. There are two main kinds of backlights used, CCFL (pictured, via Home theatre Mag) which are like the lights in your high school cafeteria), and LED, which we talk a bit more about below. There are two major kinds of LCD displays. There's the traditional twisted nematic kind (TNT), which is cheaper and known for faster response times, and then there's in-panel switching (IPS), which is more expensive and usually slower response times, buuut it's got a wider viewing angle and better colours.

On a broader level, the stuff to consider with LCD when it comes to actually buying a TV, is that, on the cheap side, LCDs tend to have worse motion and less excellent contrast ratios than plasma. You step up a bit, and it starts to even out. Especially if you pony up for the best of the best LCD TVs, typically lit up by LEDs. LCDs in general are way more eco-friendly, slimmer, and—because of their backlights—better to watch in environments where you're gonna have a ton of light spilling in.

DLP DLP is a rear-projection technology made by Texas Instruments that creates the image onscreen using a whole bunch of tiny mirrors that reflect light through a lens. The big thing about DLP sets is that they're, um, big and for cheap—a 65-inch DLP set is just $US1500. But you're probably not gonna be mounting this sucker either.

DLP is the last survivor of the "microdisplay" projection TVs, that also included LCD and LCOS techologies. They are great on contrast, but they got killed by flat panel because you can't make them an inch thick.

Laser TVs Mitsubishi's LaserVue TV is a microdisplay projection set (with a DLP chip) that is lit up by lasers instead of just focused light. Thanks to this, it delivers some of the most amazing colours and deepest blacks possible, as good as plasma sets, but at a ridiculously low power consumption. Sadly, you'll probably never buy one, and not just because it's $US5000 for a 65-inch set.

Contrast Ratio So, technically, contrast ratio is just the ratio between the brightest and darkest images a display is capable of showing, which sounds like an objective enough specification. But like many specifications, this one has been turned into a marketing tool, and subverted to a point where it is not helpful. In the lab, there are several kinds of contrast ratios: Static, which is the ratio between the brightest and darkest a screen can display simultaneously, and dynamic, which is the darkest and lightest a screen can ever be at any given time. Sadly, it's this latter figure that most TV makers brazenly display on their boxes, to the tune of ridiculous numbers like 1,000,000:1 (or more). It's utterly meaningless, and you're better off ignoring it.

OLED It's the beautiful future of television, but vastly too expensive for anyone but CEOs to own right now because OLED displays are really hard (read: expensive) to make at large sizes. "OLED" stands for organic light-emitting diode, and what's special is that the individual pixels light up by themselves, like plasma, but can be laid out on a single sheet of glass (or plastic), like LCD, so they get the best of both: They're super thin, they don't need a backlight, they have higher contrast, and they're energy efficient too. Also, they may one day—soon—be bendy!

LED TVs or LED Backlighting While a standard LCD set is lit up by a cold-cathode fluorescent lamp (think dreary lighting from high school), the best LCD sets use LEDs (light-emitting diodes). They can be configured a few different ways: Edge-lit, where the LEDs are arranged in strips along the sides of the TV, and allow it to be super-thin; and backlit, where a grid array of hundreds of LEDs sits behind the screen and, with local dimming, where clusters of lights turn on and off individually, offers the best LCD money can buy. Three of the five best TVs you can buy are LED-lit, if that tells you anything. And no, they're not cheap.

3D If you thought you heard a metric shitton about 3D this year, just wait for 2010. We have a giant primer on 3D tech right here, but there's just a couple you really need to know. Polarized 3D glasses are the cheap 3D for the masses—i.e., IMAX—where two synced projectors throw out two different images are slightly different polarizations that can only be seen by one eye at a time, making your brain see stuff in 3D without that annoying red/blue thing.

And while we kinda made fun of them, shutter glasses are actually the way 3D is moving in nicer implementations, from Panasonic and Nvidia, among others. Essentially, the glasses are battery powered, and shutters blink rapidly over each eye timed to the refresh rate of the display, so each eye sees a slightly different image as the shutter opens. It works better on plasma than LCD (even 120Hz models), in our experience.

Anti-Glare vs. Anti-Reflective Anti-glare and anti-reflective displays, surprisingly are not the same thing. Anti-glare displays often try to diffuse light coming at a display with a treated or textured surface, almost like a "matte" finish. It's about cutting back external light hitting the display, but the tradeoff is that the picture coming through may not be as clear. Anti-reflective deals with light that comes from the display itself, as well as external light, and handles this with special coatings or films that minimize reflections from all angles to make the picture clearer. (Just think about eyeglasses, with that greenish coating. Same idea.)

HDMI Honestly, the only thing you really need to know about but the High-Definition Multimedia Interface—you know, HDMI—is that the cables in most retail stores cost waaaaaay too much. If you pay anything over $US10 for an HDMI cable, you are getting suckered. Order cheaper cables from and other retailers—they do just fine as long as you're not installing them inside your walls. (If you're doing that, you should pick something heavily coated and insulated, and built to last a few generations of TV.) Oh, and there's a new version coming out—HDMI 1.4—that supports higher resolutions and internet. Not only will that require brand new HDMI cables, it will require new TVs and new content too, so it's a ways off.

Other HDTV Guides • 5 Best HDTVs Under $US10005 Best HDTVs PeriodThe Difference Between a $US600 and a $US6000 TVHow to Buy an HDTV Today (or Any Day)Picking an HDTV Like a ProHow to Set Up Your New HDTVHow to Calibrate Your New TV

Still something you wanna know? Send questions about HD, VD, and KFC here, with "Giz Explains" in the subject line.

Trending Stories Right Now