Everything You Ever Wanted to Know About HDTV

720p vs. 1080i vs. 1080p--which one is right for me?

There are two basic types of high definition TV, 1080i (i for interlaced) and 720p (p for progressive). 1080i offers the most pixels, with a matrix of 1920x1080 pixels, while 720p has fewer pixels at 1280x720 pixels. Many 720p sets are actually 768p (i.e. a native resolution of 1366 X 768 pixels). These sets convert incoming 720p signals to 768p with no loss of resolution. Both 720p (or 768p) and 1080i are considered high definiton per industry standards.

In a 1080p set the lines are "painted" on the screen progressively (as opposed to the 1080i sets in which the lines are interlaced). 1080p sets and 1080i sets have the same resolution (1920x1080 pixels), but many 1080p sets have a "smoother" appearance due to the progressive nature of the display.

In deciding which HDTV to buy do not place too much empasis on a particular resolution. There are too many other variables that affect picture quality, most of which are more significant than a set's native resolution. Find the set that looks best to you at your normal viewing distance. For most viewers that means that there is no benefit in having more pixels in a set smaller than 50 inches. Your eye cannot distinguish the difference between 720 (or 768) and 1080 sets. Signal processing, brightness, contrast, color balance, and black levels all have a more significant affect on picture quality than do the number of pixels. At 50 inches and above the resolution starts to become more relevent to picture quality, especially at closer than normal viewing distances. Buyers should consider the native resolution when shopping for one of the larger sets, but in the end it's still overall picture quality that matters most.

Almost all manufacturers are now releasing 1080p sets across all screen sizes and within a few years the question of 720p vs. 1080i vs. 1080p will be academic. All sets, regardless of size, will be 1080p. A side benefit of this transition is that, for a time, many excellent 720p sets will available at significantly discounted prices. This is a great time to find a bargain on a fantastic 720p set as sellers purge their stocks to make room for the next generation of all 1080p sets. If you have a Blu-Ray player you should consider a 1080p set to enjoy the full image resolution of Blu-Ray discs as well as most new video game systems.

Newer HDTV models support 1080p, but are generally more expensive than 720p or 1080i models. The advantages of 1080p are most noticeable on screens 50 inches or larger. It allows you to sit closer than you could with a 720p set before you begin to see the individual pixels. On the other hand, HDTV programming (cable, over-the-air, satellite) maxes out at 1080i. Still, if you anticipate using a Blu-ray movie player or playing high-def video games, you may want to invest in a 1080p TV to have maximum flexibility with your system.

What's all the fuss about HDMI connections?

Make the most of your high-definition TV investment by using the highest-quality connection: HDMI. It's a slim cord that supports all high-definition resolutions (720p, 1080i, 1080p, etc.) and can carry multichannel audio as well. HDMI is all you need to connect your Blu-ray player or digital television receiver to your HDMI equipped HDTV. By maintaining a digital signal throughout your home-theater system, HDMI avoids the digital-to-analog conversion that can degrade your image quality. Uncertified cables might be cheaper, but they could be more susceptible to electrical interference and unreliable connections or have other problems.

LCD vs. Plasma

This is a much debated topic and a fun one. When choosing between plasma and LCD TVs, you're actually selecting between two competing technologies, both of which achieve similar features (i.e., ,bright crystal-clear images, super color-filled pictures) and come in similar packages (i.e., 3.5 inch depth flat screen casing). To complicate the decision-making process further, price and size are two previous considerations that are rapidly becoming non-issues as LCD TVs are now being made in larger sizes and at competing prices with plasma.

Despite their similarities, the two technologies are very different in the way they deliver the image to the viewer. Plasma technology consists hundreds of thousands of individual pixel cells, which allow electric pulses (stemming from electrodes) to excite rare natural gases-usually xenon and neon-causing them to glow and produce light. This light illuminates the proper balance of red, green, or blue phosphors contained in each cell to display the proper color sequence from the light. Each pixel cell is essentially an individual microscopic florescent light bulb, receiving instruction from software contained on the rear electrostatic silicon board. Look very closely at a plasma TV and you can actually see the individual pixel cell coloration of red, green, and blue bars. You can also see the black ribs which separate each.

Whether spread across a flat-panel screen or placed in the heart of a projector, all LCD displays come from the same technological background. A matrix of thin-film transistors (TFTs) supplies voltage to liquid-crystal-filled cells sandwiched between two sheets of glass. When hit with an electrical charge, the crystals untwist to an exact degree to filter white light generated by a lamp behind the screen (for flat-panel TVs) or one projecting through a small LCD chip (for projection TVs). LCD TVs reproduce colors through a process of subtraction: They block out particular color wavelengths from the spectrum of white light until they're left with just the right color. And, it's the intensity of light permitted to pass through this liquid-crystal matrix that enables LCD televisions to display images chock-full of colors-or gradations of them.

CONTRAST/BLACK LEVELS

Plasma technology has certainly achieved quite high contrast ratios, a measure of the blackest black compared to the whitest white. Many plasma display manufacturers boast a contrast ratio of 3000:1 these days though our tests have not proven these numbers out. Panasonic has long been the leader in plasma black levels and we measure contrast of a 42" HD Panasonic plasma at about ANSI 1450:1 - still impressive. Plasma displays achieve such impressive black levels by using internal algorithms to block the power to particular pixels in order to render a pixel "dark" or black. While this can limit a plasma television's gray scaling, it does produce exceptionally black blacks - depending on the manufactured plasma display element (i.e. glass). A plasma TV uses the most power when it is producing full white. As a result, some 2nd tier manufactured brands of plasma TVs have an audible buzz or whining sound when displaying white or very light images.

LCD (liquid crystal diode) displays, by contrast, utilize electric charges to twist and untwist liquid crystals, which causes them to block light and, hence, emit blacks. The higher the voltage passing through the liquid crystals in a given pixel, the more fully those crystals untwist and effectively block light - all of which makes these pixels darker. As opposed to plasma, LCD TVs use the most power when displaying a very dark or black image. This is a difficult process, and despite recent improvements in LCD black levels, only the best LCD televisions (like those produced by Sharp and Sony) have managed to topple the 1000:1 contrast ratio barrier. Recent improvements have brought LCD displays up to the level of plasma. The one continual drawback here for LCD is off axis viewing, when black levels consistently drop.

COLOR ACCURACY

In plasma displays, each pixel contains red, green, and blue elements, which work in conjunction to create 16.77 million colors. Insofar as each pixel contains all the elements needed to produce every color in the spectrum, color information was more accurately reproduced with plasma technology than it was with other display technologies. The chromaticity coordinates were more accurate on most plasma displays. Though the color saturation resulting from the pixel design of plasma displays is remarkable, LCD technology has nearly caught plasma in gray scaling color accuracy. Plasma continues to exhibit more richness in color information and more natural coloration. Today, SMPTE color coordinates in top plasma displays still normally outperform those in LCDs, which tend toward oversaturation.

LCD TVs reproduce colors by manipulating light waves and subtracting colors from white light. This is an inherently difficult template for maintaining color accuracy and vibrancy - though most LCD displays manage quite well. While color information benefits from the higher-than-average number of pixels per square inch found in LCD televisions (especially when compared to plasmas), LCDs are simply not as impressive as plasmas with similar pixel counts. LCDs however, produce a typically brighter picture. Greens sometimes look over-green and reds can run a bit warm, but in a room with bright outdoor lighting, an LCD TV would be my choice.

VIEWING ANGLES

Plasma manufacturers have made much of their 160° viewing angles, which is about as good as horizontal and vertical viewing angles get. This owes to the fact that each pixel produces its own light, rather than light being spread across the screen from one central source. Hence, each pixel is more readily visible because its brightness is consistent with every other pixel on the screen. One consistent area of superiority of plasma viewing angles is demonstrated when viewing dark material content, especially DVDs. A Plasma display holds the black levels from off axis, while LCD TVs lose black level intensity more as the angle off axis increases. This usually occurs after around 90 degrees.

LCD TV manufacturers have done much to improve their displays' viewing angles. The substrate material on newer-generation LCD models by Sharp and Sony has helped to expand those units' viewing angles, though they still have some ground to cover before catching plasma. Expect the best LCD HDTVs to have between 120 and 130 degree viewing angles.

FAST-MOVING VIDEO PLAYBACK

Plasma gets the nod here because of their excellent performance with fast-moving images and high contrast levels. There are still some 2nd tier manufacturers whose plasma product displays some phosphor lag, a drag time in scenes changing from bright to dark.

While the "response time" of LCD TVs has markedly improved in the last couple of years, they still suffer from a slight "trailer" effect, where the individual pixels are just slightly out of step with the image on the screen. During fast moving sports scenes, the most discerning eyes can detect this slight motion response lag.

LONGEVITY

LCD television manufacturers claim that their displays last, on average, 50,000 to 65,000 hours. In fact, an LCD TV will last as long as its backlight does - and those bulbs can sometimes be replaced! Since this is nothing more than light passing through a prismatic substrate, there is essentially nothing to wear out in an LCD monitor. However, one nasty little known fact about LCD technology is that as the backlight ages it can change colors slightly (think of florescent office lighting). When this occurs the white balance of the entire LCD TV will be thrown for a loop and the user will need to re-calibrate, or worse, try to replace the backlighting or ditch the unit altogether. Some of the early purchasers of larger LCD screens will be learning this tidbit in a couple of years. One thing that I've found in this industry, it is not easy to find out whether the backlighting on LCDs can be replaced. Manufacturers are either hesitant to discuss the topic, or they just don't know.

Plasma, on the other hand, utilizes slight electric currents to excite a combination of noble gases (i.e., argon, neon, xenon), which glow red, blue, and/or green. This is an essentially active phenomenon, so the phosphoric elements in plasma displays fade over time. Many manufacturers state a new half life of 60,000 hours. While I am skeptical of this spec, I do believe strides have been made to nearly even the playing field with LCD. At half life, the phosphors in a plasma screen will glow half as brightly as they did when the set was new. There is no way to replace these gases; the display simply continues to grow dimmer with use.

ADVANTAGE: Even, depending upon manufacturer quality.

SCREEN BURN IN

LCD technology is not prone to screen "burn-in" or "ghosting" (premature aging of pixel cells) due to the nature of the technologies "twisting crystals."

With plasma, static images will begin to "burn-in," or permanently etch the color being displayed into the glass display element. The time it takes for this to occur depends greatly on the anti burn-in technology of the manufacturer. Recent improvements by plasma manufacturers have certainly extended the time it takes to burn in a plasma pixel cell. In the past I was concerned to place a DVD on pause 15 minutes. Now, many of the enhancements such as better green phosphor material, and motion adaptive anti burn-in technology are greatly reducing the risk of burn in. It's gotten so much better that I don't even worry about it anymore. In a new model plasma from any top tier manufacturer I would put "ghosting" estimates at an hour or more now (Ghosting can be "washed" out by displaying static gray material). Permanent burn-in I would put at more than 10 hours.

PRICE AND RESOLUTION

LCD HDTV displays will have a higher resolution per same size comparison than plasma. The lowest resolution of a 40 inch LCD will be 1366 X 768 - easily full HD resolution in 1080i or 720p. A 42 inch HD plasma has a resolution of 1024 X 768. While this is not truly an HD resolution, it's close enough so that it's difficult to know the difference. A 50 inch plasma TV will have a resolution of 1366 X 768, while a 45 inch LCD displays 1920 X 1080 (1080P) resolution.

Those extra pixels and the production process of LCD HDTVs cost more money to produce. Expect to pay a third as much more for a similar size LCD TV than a plasma display.

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