High Definition TV (HDTV) Features

Snapshot:

• For HDTVs:  LCD displays are getting popular in sizes up to 52 inches.

• Plasma displays: very competitive for 50 inch sizes and bigger.

• Rear projection TVs: have the best prices per screen size.

• Front projection TV: a great home theater centerpiece, but works best in darkened rooms.

• TV under 40 inches: 720P resolution works great.

• TVs over 40 inches: 1080p is the new standard. 

OK, you're ready to shop for a new TV.  This section provides an overview of the different technologies and features you'll find on HDTV models. 

As discussed earlier, there is no reason to by any type of TV other than an HDTV, which will be labeled "HDTV."  When you buy an HDTV, you will get a set that:

• has a WIDESCREEN, 16:9 ASPECT RATIO screen.  HDTV programs are produced in this screen shape.
• can display a "resolution" of at least 720 lines (the number of  horizontal lines used to create the TV picture).  
• has a DIGITAL or ATSC tuner to receive local DIGITAL TV channels with an ANTENNA.
• has the ability to display all of the HDTV formats (and other digital formats) that broadcasters might use.
• probably has all the connections needed to connect any kind of video or audio device to the TV. 

Of course, with the above features, an HDTV is capable of creating stunning, crisp pictures with terrific detail and realism - adding a new dimension of excitement to TV viewing.  And that's why you're planning to get one, right?

While dozens of HDTV sets lined up on a store wall may look pretty much the same, there are several key differences in HDTV technology that you should be familiar with: display types; horizontal resolution, and connection features. 

HDTV Display Types

There are basically four ways to create an HDTV picture, and each of these "display types" has its own virtues and quirks.  When shopping for an HDTV, you will see nearly all of these.  Here's information on each one.

1.      LCD.  Stands for Liquid Crystal Display.  This display is basically super-sized computer screen technology.  It is based on a screen that has a light source behind it, usually a flourescent light. In front of the light, there are red, green and blue "windows."  In front of the windows are crystals that operate like window shades.  An eletrical charge from the TV electronics tells a crystal to open and pass the colored light, or close and block the light.   An HDTV screen has hundreds of thousands of these windows.  Operating together, these windows create a picture on the screen. 

LCDs are the most expensive display to manufacture per picture area, but their crisp, precise images have made them a popular choice for HDTVs, even at screen sizes up to 50 inches (diagonal meaure). 

Used for: smallest HDTV screens (basically, screens of 17 inches or so) up to 52 inch screens. 

Advantages.  Bright images. Lightest weight sets for the screen size. Have little screen reflection (the screen faces are a vinyl material).  Won't get "burn in" from showing a constant image.  Run cooler and may use less power than PLASMAs. 

Disadvantages.  Generally have a price premium versus same size PLASMA sets. May have a narrower "viewing angle" than PLASMA TVs. Can be slower to respond to picture changes, causing bluriness in sports and fast-moving scenes. 

Trends.  There are several upgrades being offered to improve LCD displays:

Faster response times.  Typical LCD "response times" for the crystals is 8 milliseconds.  Newer screen designs can produce 6 millisecond, and even 4 millisecond, response times.  

120 cycle refresh.  HDTV uses a "frame rate" of 60 frames per second, meaning that the picture gets "drawn" 60 times each second.  The problem with this, particularly for LCD displays, is that on a big screen, that's not often enough to keep up with fast changes in the picture.  The solution: double the frame rate to 120 frames a second and create pictures twice as often. This can noticeably improve the performance of an LCD screen, and many retailers show a side-by-side demonstration of HDTVs with 120 and 60 cycle refresh to show the difference.  This feature can cost more.  

LED backlight.  LCD screens have typically used a white flourescent light to illuminate the screen.  The problem is that, when the LCD crystals are "closed" to create a dark picture, light still leaks through the screen.  So it's hard for an LCD screen to create a deep "black."  Manufacturers have now figured out how to use LEDs (light emitting diodes) as backlights. The LEDs can provide different colors than just white, which adds to the color output of the screen, and they can be quickly turned off for dark scenes, creating darker "black"  areas on the screen, and thus more screen contrast.  LED backlight is an expensive addition now, but the price is coming down. 

2.      PLASMA.   A PLASMA screen is a huge matrix of tiny flourescent lights.  Each "light" is a gas-filled cell that lights up with a color of red, green, or blue when it gets an electrical charge.  Three different-colored cells work together to create one pixel of light.  To create a picture on the screen, the TV electronics send electrical charges to each color in each pixel; the cells then light up to create a combined color with the required  brightness.  All the pixels together create a picture on the screen.

Plasma displays used to be the leading display for screens over 40 inches, but LCDs overtook them, primarily because they offered "1080p" resolution at the larger sizes, while plasmas tended to offer "720p" resolution.  But plasmas are now available at 1080p resolution.  They are very comparable to LCDs in brightness and viewing angle, and cheaper for the same screen size, so they are competitive again in the category of 50 inch screens or larger. 

Used for: primarily 50 inch screen models and larger, though there are some plasma models in the 40 to 50 inch category.

Advantages.  In the flat screen category, plasmas are generally cheaper than LCDs for the same screen size.  They can show deeper blacks, which also provides more picture contrast.  They have a faster picture reaction time, so they can look better showing action and sports scenes, with less blur. 

Disadvantages. They are heavier than LCD sets of the same screen size.  Most models have glass fronts, which can cause more room light reflections, and it makes them more fragile.  There is a slight possibility of image "burn in" if one image stays on the screen for long periods of time.  At altitudes of 5000 feet or higher, the cheaper brands can have a noticeable buzzing sound.  There are fewer choices of 1080p models.

Trends.  Some features being offered on plasmas are:

Anti-glare filters on the front screens, to reduce room reflections. 

High altitude engineering.  Eliminates the chance of a "buzzing" sound when the TV is used at an altitude up to 9000 feet.  Look for this feature if you live above 4000 feet or so. 

"Moving pixel" technology. The TV moves pictures slightly and imperceptibly on the screen to avoid "burn-in." 

3.     REAR PROJECTION TV.  This is a TV display based the on concept of projecting an image on a screen, as in a movie theater, with one change: the image is projected on the rear of a screen that you can see through.  A single light source (which can be a lightbulb or LEDs) shines through an engine that turns the light into a picture; the picture is reflected by mirrors onto the back of the transparent screen, and the entire system is inside the TV enclosure.

Rear projection TVs have always offered the biggest screens for the money versus PLASMA and LCD displays.  They are the deepest sets, since they need room in back to reflect the picture, but they've gotten much slimmer as optics have improved.  To make best use of the projected light, the screens are designed to aim the brightest picture to viewers straight in front of the cabinet.  Due the rising popularity and larger available sizes of flat panel displays, sales of rear projection sets are declining and about half the major TV brands don't make rear projection sets .    

Used for: screen sizes of 50 to 65 inches. 

Advantages.  Lowest cost per screen size versus flat panel displays.  Nearly all models offer 1080p resolution.

Disadvantages.  Rear projection TVs have the deepest cabinets, at 12 to 22 inches depth.  The image brightness falls off quickly as you move from the front of the screen.  Models with bulbs may require their replacement, which can sometimes be done by viewers, or could cost up to $300.

Trends. 

Displays with "DLP" processors have been popular, but "LCoS" technology ("Liquid Crystal on Silicon") provides similar pictures without any "rainbow" effect that some viewers detect from DLP sets. 

Improved light sources are being developed: some have LED lights, and one manufacturer is developing a laser light source. 

4.      FRONT PROJECTION TV.  This display simply uses a projector to shine an image on a screen, as in a movie theater.  An HDTV projector, usually positioned above or behind the viewing area, shoots a bright light through a technology that converts the light to a TV picture; the picture goes through a lens that adjusts the size and focus of the picture and aims it at a screen.  Sound must be provided by a separate loudspeaker system.

Front projection HDTV systems can produce the largest pictures of any technology (and the size can be changed just by changing the lens "zoom").  Because of the size of image they can provide, they create the most stunning and engaging HDTV viewing experience, which rivals movie theaters. Thus they are often used as the centerpiece of of a home theater system.  But they don't rival other technologies in picture brightness, and the viewing area of a projection system usually needs to be dimmed to provide the most enjoyable viewing. 

Used for:  Pictures 6 feet diagonal and larger.

Advantages.  Can create the most engaging and immersive video viewing experience.  Will enhance every video source: DVD, games, etc.  Requires very little space for a projector, which can be mounted above or behind the viewing area.  Projectors offer 1080p resolution.  Cost per picture size is low. 

Disadvantages.  Less bright than other displays; works best in a dimmed room.  Requires a separate sound system.  Requires installation of a permanent or movable screen.  Has a bulb that may need replacing (but replacment is easier than on a rear projection TV).  Requires connections among the projector, HDTV signal sources, and sound system.  Projectors have cooling fans which some viewers may find irritating.  May require a professional installation.  

Trends.  Projectors have used "LCD" and more expensive "DLP" displays.  Newest models feature "LCoS" displays, which offer very sharp pictures and good contrast with no "rainbow" effect that some viewers detect from DLP projectors. 

Horizontal Resolution

This is the number of horizontal lines that are used to create a TV picture.  The HDTV standard includes two kinds of resolution, and all HDTV sets are built to display one kind of resolution "naturally" and the other kind with some electronic manipulation.  

720p Resolution.  (This is basically the same as "768" resolution).  In this HDTV standard, there are 720 lines to a picture, and they are drawn 60 times a second in a "progressive" order (top to bottom; line 1, line 2, line 3...).  Nearly all HDTVs under 30 inches, and most HDTVs under 40 inches, use 720p resolution.  At these screen sizes, it is nearly impossible to tell the difference between 720 and 1080 resolution. 

So on smaller HDTV sets, 720p resolution is common and works well. 

1080i/p Resolution.  In this HDTV standard, there are 1080 lines to a picture.  In early HDTVs, the standard was "1080i," which draws the lines 30 times a second in an "interlaced" order (top to bottom, line1, line 3, line 5...then line 2, line 4, line 6...)  Currently, any TV broadcasting that uses 1080 resolution does it in 1080i.  While it may seem that more lines would equal a better picture, that's not absolutely true, since 720p and 1080i broadcasting deliver nearly the same number of pixels on a screen every second.  So until recently, 720p and 1080i have looked comparable at any screen size. 

But: 1080i has undergone a change.  Manufacturers have figured out how to build HDTV sets with 1080p resolution (60 pictures a second in progressive order).  While there are no broadcasters using 1080p production, video game consoles and high definition DVD players can provide a 1080p output.  On screens larger than 40 inches, an HD source of 1080p, such as a DVD player, provides a picture that is even better than broadcast HD.  And when 1080p is compared to a 720p screen of the same size, it looks better because it has more lines and is also progressive. 
If you plan to watch sources of video that can provide 1080p resolution, such as DVD players, video games, or computers, then, for a screen size of 40 inches or more, you should look for a set with 1080p resolution. 

Connection Features

You will want to use your HDTV to display video from any source, including cable or satellite TV, DVD, video game, computer, VCR, camcorder, digital camera - anything that can create an electronic picture.  Some of these have modern connections for video and sound; some have the oldest connections.  Nearly all HDTVs today have connections for all sources.  Before you shop, list all the video sources you might watch on your HDVT,  the kind of connections they use, and how many for each type of connection. 

The key items to check on HDTV connnections are:
-for each connection type, are there enough jacks (holes) for the number of devices you will connect at the same time?
-do you have any unusual connection needs, such as VGA for an older computer?
-for convenience, do you want a one of the connections to be on the side or front of the TV?

These are the typical connections available on HDTVs:

HDMI.  The newest, simplest and most comprehensive connection for video devices.  Carries full digital HD video and sound in one simple cable.  The HDMI standard is evolving, and the latest version is 1.3, but any version of HDMI will work with any other.  Most HDTVs have at least 3 HDMI connections; some as many as 4. 

COMPONENT.  A high quality video connection that's been around longer than HDMI.  Uses 3 wires, with plugs colored red, green, and blue (so they are sometimes called an "RGB" connection).  Component connections handle picture signals only, in an analog format (a separate connection for audio is required). 

S-VIDEO.  A video connection that is used to send just a TV picture from one video device to another.  It is higher quality than the basic COMPOSITE or "RCA" video connection (usually colored yellow), but much lower quality than COMPONENT.  Requires a separate connection for audio. 

COMPOSITE or RCA connection.  Is the oldest and simplest connection that is used to send a TV picture (and usually one or two sound channels) from one video device to another.  It uses a cable with three wires, with yellow plugs (for video), white plugs (left channel sound), and red plugs (right channel sound).  Composite connections are also called "RCA" (the name of the round plugs) connections.  Older video devices such as VCRs may have only this connection. 

Computer display connections.  DVI (Digital VIsual Interface) and VGA.  These connections match the newer DVI display outputs of computers and the older VGA outputs.  If you use them, you many need to adjust the video settings on your computer to get the image to fit on your HDTV screen.  These are video-only, and require a separate connection for audio. 
DIGITAL AUDIO (also called S/PDIF for "Sony Philips Digital Interface," the inventors).  These are used to connect digital audio from a source (HDTV, DVD, SET TOP) to a sound system.  They can use a wired cable (orange plugs) or an optical fiber cable, called a TOSLINK.  If HDMI connections are not available, these are the highest quality sound connections to use. 

Ethernet connections.  Can be handy for connecting the HDTV to a computer or computer network to access video, pictures, and Internet video.

ANTENNA.  Yes - the same connection as 60-year-old TVs: connects to an antenna.  Some HDTVs have two antenna connections, which could be handy for switching between different antennas. 

Other HDTV features.  These will come up when you're shopping for an HDTV:

ANALOG or "NTSC" tuner.  This is the ability to tune regular ANALOG TV channels.  Make sure the HDTV has it.  As discussed elsewhere on this site, LOW POWER and TRANSLATOR TV stations will continue to broadcast ANALOG TV channels next year and for the forseeable future, and there are probably some in your area.  If you'll ever watch TV OVER-THE-AIR with an antenna, you'll need an analog tuner to watch these stations. 

Contrast ratio.  This is the difference between the brightest and darkest images a TV screen can produce.  HDTVs today are promoted as having contrast ratios of 10,000 to 1 and 15,000 to 1, and they have improved a lot.  But: there is no common standard for measuring contrast ratios, so the numbers your see are only mildly useful for comparing TVs from the same manufacturer. 

Nearly all HDTVs can produce a very bright picture.  There is more variance in how dark a picture they can produce.  If you like to watch TV with lights dimmed for a theater effect, compare how well HDTV models can create a dark picture.  

Internet video links.  Manufacturers are starting to offer devices you can purchase to connect to their HDTVs that provide Internet connections and let you watch Internet video.  This is an exciting new development, but the content available through their devices is usually limited to the video providers that manufacturers contract with - which is NOT unlimited access to Internet video; plus, most of the content is not HDTV quality. 

The way that Internet connections to TVs are most likely to evolve is based on users selecting their own systems for video access, whether it's with a computer with Windows Media Center softare or a dedicated TV platform like a TiVo or AppleTV. 

CableCARD.  This is a technology that was created by the cable TV industry and the consumer electronics industry that was supposed to replace the need to have a cable SET TOP connected to a TV to watch cable channels.  The idea is that the TV or similar device has a special "slot " for the CableCard.  A CABLE TV subscriber then rents a "CableCARD" (looks like a plug-in card for a notebook computer) from his cable company.  The CableCARD performs the same functions as a cable SET TOP, which is primarily to decode premium channels.  But current CableCARDs only support "one-way" services, and not "two-way" services like video-on-demand and interactive TV that require a signal to go back up the cable.  Plus, TVs with a CableCARD slot are more expensive. 

Because of these limits, CableCARDs have remained a fringe technology. And more cable subscribers are getting a cable SET TOP anyway because they want the DIGITAL VIDEO RECORDER (DVR) and video-on-demand features.  So unless you want to watch premium cable channels without renting an entire cable SET TOP, a TV with a CableCARD slot will probably not be important.

More answers for the very curious.  

Does an HDTV turn all the programs into HD?  No.  Only shows produced in HD will appear in HD, and only if the signal source (cable TV, antenna, or other) is providing an HD signal to the HDTV.  Otherwise, an HDTV will take whatever picture it gets and try to make it look nice, but it won't be HD quality. 

I've seen widescreen TVs in public and they make everyone look fat.  Will my HDTV do that?  Aha - you've spotted the greatest crime in TV land -  stretching non-HDTV programs to fit on a widescreen TV.  Those TVs are receiving a traditional channel with a 4:3 ASPECT RATIO plugged into the widescreen TV.  Normally, the picture would just fill the middle of the screen, leaving black bars on the side, called a "PILLARBOX."  But because that picture doesn't fill the expensive screen, the owners will set the TV to "stretch" the picture sideways. It fills up the screen, but it makes everyone look fat.  The solution is to use a true HDTV program source, which will properly fill a widescreen HDTV.  

When I watch HDTV, why do the pictures change in quality?   This is because the picture is changing between programs that are produced in HD, with high quality, and programs or commercials that are not produced in HD, so they are "upscaled" by the network or the TV itself to fill the screen.  This can be obvious when a program produced in HD switches to a commercial.  As more programs are produced in HD, this will happen less often. 

When I'm shopping, I see HDTV's marked with "768" resolution, but publications say HD is "720" resolution. What's the difference?  Great question, and one that is not well-explained by manufacturers.  The short answer is: treat them the same.  The longer answer is: "768" lines of resolution is part of a widescreen computer display standard (1366x768).  The electronics for supporting this display are widely available, so some HDVTs have simply adopted the 1366x768 hardware for their displays.  But: an HDTV picture sent at 1280 x 720 will be too small for that, so the TV must "upscale" the picture a little, to fit the bigger display. (It must also "downscale" an HD show in 1920 x 1080 resolution). The quality of the SCALING is what distinguishes better HDTV sets, so compare the pictures on "768" sets carefully.  

What is "true" HD?  This is a marketing term used for HDTVs that have "1080p" resolution.  This is the highest quality HD display that is available.  But the other main HD formats that TVs are built to display (1920 x 1080i and 1280 x 720p) are defined in the digital standard as true HD as well.

Will my HDTV become obsolete if I buy a "720p" model and more programs are produced in "1080i" resolution?   No, the HDTV standard requires TVs to be able to display both sources.  720p will continue to be popular for TVs under 40 inches, and especially under 30 inches, where it's hard to see a difference between 720 and 1080 displays.  And it won't be obsolete no matter what the size. 

Why do HDTV screens use red, green, and blue lights?  Basic physics!  All color TVs and monitors use these three colors.  Red, green, and blue are the primary colors of light.  By shining these colors together and changing their individual brightness, TVs can create nearly all other colors. The three colors together produce white, and when they're all off, the image is - black!

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CAPITALIZED WORDS are defined in the Digital TV Glossary.