1080p
An HDTV sporting a native resolution of 1080p has the capability of displaying video with 1,080 lines of vertical resolution. The "p" in 1080p means that it can display — as long as the input signal allows — progressive scan video. That is, every line of a video image is output for every frame. This differs from interlaced video, or 1080i, which scans only half of the lines, then the other half, for each frame of video. At this point in time, 1080p — also known as Full HD, True HD, or Ultra HD — is the high water mark of resolutions and it will be able to display all kinds of HD video (cable, Blu-ray discs, etc.).
There is a new standard currently being developed called QuadHD or 2160p. It has a 3,840 x 2,160 resolution (four times that of current 1080p resolutions) and is estimated to hit the market in 2010. With no content currently being sold to consumers in this resolution, even if the screens make it to market next year, there's no reason to become an early adopter. If you're thinking of buying a new TV, don't put off buying a 1080p screen in the fear that it will be out-dated by this new technology any time soon.
Refresh Rate
Most LCD TVs refresh their images at a rate of 60 times per second, or 60Hz. This is perfect for video signals, as they come in at 30 frames per second, so each frame is refreshed twice, clarifying the image. However, since everything captured on film was recorded at 24 frames per second, a 60Hz refresh rate gets in the way. In order to display a movie, your hardware does something called "2:3 pulldown" — essentially, it takes the 24 frames of the film image (from a DVD or what-not) and displays the first frame three times, the second frame twice, then the third three times, and on and on. When displayed on large TVs, this work-around can become very apparent, revealing itself through jerky motion called "judder" and blurring of the image during scenes with fast motion.
120Hz televisions refresh the image 120 times a second which works out perfectly for both video at 30fps and film at 24fps because each frame can be refreshed at a constant rate. (Four times for video, five for film.) The result is smoother and clearer images — especially during action scenes and sports events. (The image on the left shows motion blur, whereas the image on the right features 120Hz technology.)
240Hz refresh rate TVs are currently being pushed by TV makers as the best quality available. They also add a premium price, too. However, for 99% of consumers, a 120Hz will suit all TV-watching needs just fine. Why? Because 240 is also a multiple of 24 and 30, therefore the difference between 120Hz and 240Hz is not as apparent as the difference between 60Hz and 120Hz is. In fact, side-by-side, the improved quality of a 240Hz screen over a 120Hz is barely noticeable.
Brightness
Brightness is the measure of the intensity of light your panel is capable of emitting. It's listed as how many candelas per square meters (cd/m²) or as "nits" (one candela per square meter) the panel emits. A candela is equivalent to the amount of light a single candle emits. Therefore, an LCD with a brightness of 300 cd/m² (or 300 nits) is capable of emitting as much light as 300 candles in a square meter of space do. Naturally, a higher brightness number means a brighter picture. This specification of an LCD is more important for TVs which will be viewed in an environment with a lot of light, as you'll want your screen to be able to overcome the ambient environmental light.
Contrast Ratio
Technically, dynamic contrast ratio is the difference between the darkest dark and the brightest bright over time, while static contrast ratio (sometimes called native contrast ratio) is the difference in luminance which can be displayed within one static image. However, the astronomically huge numbers the manufacturers present in these ratios are mostly meaningless to the consumer as a tool for comparison. This is because the reporting of these ratios have no cross-industry regulations or guidelines on how they are measured. Therefore, manufacturers can derive these numbers however they want.
The only instance where these ratios can be an effective comparison tool is between models of the same brand. Since one can assume that a manufacturer is using the same metrics to judge all of its TVs, its ratios are meaningful only within its own line of TVs. In these cases, the consumer should look for a higher ratio.
Even when comparing between the same brand, however, dynamic contrast ratio reporting is the least informative, as it's the sum total difference of what the panel can display (sometimes including the "off" state of the TV), not what it's capable of displaying within one static image. A better measure is the static contrast ratio. A higher ratio here will mean that when watching content, your TV will be better at displaying dark images with small spots of light (or vice-versa) without the overall image blurring or looking dim.
Response Time
Response time, measured in milliseconds (ms), is the time it takes a pixel to change from black to white, then back to black again. The smaller this number is, the better a panel will be at handling video signals with a lot of motion in them.
That said, the difference between a 10ms response time and anything faster is almost imperceptible to the human eye. Look for TVs that have less than 10ms, but don't pay a lot more for a faster response time. However; anything slower than 10ms could result in blurring or ghosting — leaving behind a fading trail of an after image — in video images with a lot of motion in them.
An additional note: Many manufacturers have begun listing their response time as the time it takes for a pixel to go from gray-to-gray without the pixel ever entering a fully on or off state. This can lead to some wildly inaccurate information, since there's no industry-wide guideline as to what a "gray state" is. To ensure better picture quality on your TV, look for a black-to-black response time.
Built-In Tuners
- NTSC (National Television System Committee)
This technology, that TVs have had for the past century, is currently useless as the U.S. has switched to digital broadcasting. - ATSC (Advanced Television Systems Committee)
This digital method of image transmission allows for over-the-air reception of HD content with resolutions up to 1080i. If you do not subscribe to cable, satellite TV, etc., this is a very important tuner to have. - QAM (Quadrature Amplitude Modulation)
This tuner allows your television to display unscrambled digital cable signals without the aid of a set-top box. However, in many cases this will result in the ability to receive only your local network affiliate channels (there's a law against cable providers scrambling those), but not premium channels like HBO.
Video Inputs
- HDMI (High-Definition Multimedia Interface)
This type of cable carries both digital video and audio signals on one cable. Along with the benefit of decreasing the number of cables stuffed behind your entertainment center, this all-in-one solution can transport digital video resolutions up to 2560x1600 and up to eight channels of audio. It's your best bet for carrying high-defintion content output from cable boxes, Blu-ray players, or set-top video streaming devices (like the Vudu or Roku boxes.) - Component Video
This analog solution to video transport is a bundle of three wires which each carry one of three color information signals (Red, Green, and Blue.) As with HDMI, this type of cable carries HD video (up to 1080p), but its signal must get converted from digital to analog at the output source, then back to digital at the television. Many claim that this creates poorer quality and a greater chance of "noise" in the displayed image. Besides that, the real benefit of HDMI over component is that, since component only carries video, it needs to be paired up with analog or digital audio cables for audio transport; as mentioned before, HDMI does it all in one cable. - VGA (D-Sub 15)
If you want to use your TV as a media center, this type of input is one to look out for, since VGA outputs can be found on most computers. The VGA cable carries an analog video signal only; no audio information is transmitted. Even though VGA can handle 2048x1536 video, the resolution you'll get to display on your TV is limited by the type of graphics card you have in the computer (some export higher resolutions than others). Most panels will adjust their display resolution to accept the incoming VGA signal, but if you want a higher resolution, be sure to check your video card's maximum resolution output. - DVI (Digital Visual Interface)
This is another, although better, input to look for if you want to connect your TV to a computer. Unlike the analog VGA, which often suffers from interference and distortion, DVI transmits all the picture information digitally, pixel by pixel, to yield a higher quality image. Like VGA, this type of connection does not carry audio. A single DVI connection can transport video with up to a 1920x1200 resolution at 60Hz. (Dual-link DVI can carry up to 2560x1600, but it's primarily for use with computer monitors and is not found on TVs.)
10-bit vs 8-bit Processor and Panel
The thousands of pixels on an LCD display are comprised of red, green, and blue sub-pixels. Each of the three are all capable of illuminating at various intensities. A sub-pixel on an 8-pit panel can generate 256 distinct levels of illumination. A 10-bit sub-pixel can create 1,024 levels. That means that, in theory, a 10-bit display is able to produce more colors, smoother transitions between adjacent pixels, and the elimination of "banding" or "raster" of a displayed image. (The sunset image on the bottom displays no banding, whereas the top image, using standard color, is less smooth.)
LED (Light Emitting Diode) vs CCFL (cold cathode fluorescent lamps) Backlighting
An LCD screen, in order to be seen easily by the naked eye, needs to be backlit. (Think of when you tried to play an old Gameboy in the dark.) Most panels use CCFL bulbs to add this illumination, although many of the higher-end TVs use LED backlighting. LEDs have the advantage over CCFLs for several reasons. Firstly, CCFLs add more bulk than LEDs do — you can get a thinner TV with LED technology. Secondly, LEDs have a longer life-span than CCFL. Thirdly, over time, the environmentally-dubious gases inside CCFL bulbs wear out, decreasing their effective output of illumination.
There is one further differentiation within LED backlighting technologies to note. Most LED backlit panels rely upon white LEDs for their illumination. However, a new technology, called RGB LED backlighting, swaps out the white LEDs for clusters of red, green, and blue LEDs. This technology purports to display sharper primary colors, more accurate color reproduction, and the ability to produce darker blacks and brighter whites within the same image by selectively turning on and off individual clusters of LEDs.
Hopefully, you should now be comfortable enough to face the abbreviation-soaked techno-speak of the world of LCD TVs. Check out our LCD HDTV section for deals on both high-end and entry-level models.
Jeff Somogyi is dealnews' Media Editor
New to dealnews? Click here register now.