HDTV Hints Part 1: Selecting a TV

By Mike on 3:14 pm

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Even for tech minded people, the world of HDTV can be a confusing one. So, lets take a look at where to begin.

Picking a Set

There's a huge number of HDTVs available for sale right now in a wide variety of formats, types, prices, and sizes. Screen size doesn't really matter. Before you go out looking, set an appropriate budget that you know you can afford. There are many tempting credit financing offers out there for large TVs, but this is not a car. Don't buy it if you don't have the cash to back it up.

Resolution: TVs generally come in several resolutions. In North America, we use NTSC picture format for standard definition broadcasts. It's sometimes referred to as 480i. The "i" stands for interlaced. That means that screen displays every other line of the screen 60 times a second, or 30 full frames per second. In layman's terms, the image is weaved onto the screen. Another common resolution is 480p. The "p" stands for progressive scan. Rather than weaving the image, it displays the whole image one frame at a time, 30 times per second. Interlacing is better for fast motion while progressive is better for still images. However, progressive resolutions are higher since interlaced technology only displays half the resolution at one time. Therefore, buy an HDTV by it's highest progressive scan resolution.

Here are some common resolutions
480i: NTSC resolution of 525 lines, 486 visible. This is what regular TV is aired at.
480p: Sometimes referred to as "enhanced definition". It has a resolution of 720x480 pixels
720p: The most common HDTV format. Resolution of 1280x720 pixels at up to 60fps.
1080i: The second most common HD format. 1080 visible lines, interlaced at 60 fields/second
1080p: Also known as "true HD". It has a resolution of 1920x1080, the highest HD resolution.

Since this is a North American blog, I've intentionally left out the PAL and SECAM formats, which are not used here. All HDTV resolutions are in the 16:9 widescreen format. That means that a screen 16'' long would be 9'' tall. This is the TV's aspect ratio. Standard definition can air in ratios of either 16:9 or 4:3, with the latter being the most common.

Contrast Ratio and Response Time:
Contrast ratio determines how a screen shows blacks and whites. On screens with a low contrast ratio, say 500:1, blacks can appear as a washed, dark gray colour. Higher ratios produce deeper blacks. I suggest starting at a minimum of 700:1 for an LCD screen. Higher is better. Watch out for "dynamic contrast ratio" though. This is a marketing gimmick where the screen adjusts lamp brightness to make it seem like it has a higher contrast ratio than it actually does. Go by its "native" contrast ratio when selecting a screen. All TVs have a contrast ratio but Plasma, CRT, and DLP already have ones so high, you won't notice a difference between sets. The contrast ratio is usually not listed in specifications for TVs other than LCDs
Response time on LCD TVs determines the minimum amount of time it takes to change the colour or brightness of each individual pixel. This is usually measured in milliseconds. On an LCD TV, look for 8ms or lower. Higher response times can produce an undesirable effect called ghosting, which leaves noticeable after images on the screen. Plasma, DLP, and CRT displays have very low response times.

Brightness and Dot Pitch
Brightness, obviously, is a number that denotes how bright a screen is. The maximum brightness is rated in Lumens. You want a screen with high lumens if you intend to put the TV in a brightly lit room. You can usually tell by eye rather than by number if the TV is suitable.
Dot pitch is how far apart individual pixels are on a screen. High dot pitch numbers give a noticeable screen door effect. Lower is better. However, this is not really an issue until you get into large TV or projection screen sizes.

Types of Displays:
There many different types of TVs to choose from. Picking the one that's right for you depends largely on the room you'll be putting it in, and you're budget. Here are a few of the most common.

-LCD TV: Liquid Crystal Display TVs are by far the most common HDTV type. You're probably familiar with this type of display. Most computer monitors are LCD, as well as screens on digital watches, MP3 players, etc. They are usually the cheapest HDTVs and offer average to good picture quality. You'll want at least 700:1 contrast ratio but higher is better. My computer monitor for example uses 2000:1, which is excellent and will offer the better image quality. A 8ms response time is a good place to start but go as low as possible. LCD TVs are usually small to large in size. They are light weight, flat, and can be mounted on a wall. LCD TVs can also double as large computer monitors. They are also usually the cheapest.

-Plasma: Plasma used a plasma gas and phosphorus to create an image. Like LCDs, these TVs are also light weight and flat. They provide a good picture but can suffer from something called plasma burn-in. This is caused by the prolonged display of still images on the screen. Newer TVs don't suffer from this problem though but older ones can. Out of the flat panel TVs available, Plasma produces the best images with the best contrast ratios. They also come in larger sizes than LCD TVs too but are more expensive.

-CRT: Cathode Ray Tube. The classic TV that we all know and love. These TVs provide the best image quality, which is far superior to newer technologies. However, they are bulky. They're heavy and take up a lot of space. As such, they're rarely bigger than 30''. These TVs are getting less common and can typically only display interlaced HD signals. There are very few HD capable CRTs on the market.

-DLP: Digital Light Processing. This technology uses thousands of tiny mirrors on a microchip to produce an image. It's a part-mechanical process rather than pure electronic like the above technologies. These are only available in projection TVs. They produce a very high image quality, close to CRT. They can produce a rainbow effect , which is common on cheaper DLP sets but is generally not a problem on decent ones. Since it's only in projection TVs, screen size is variable. Like plasma, they produce the best HD pictures and have high contrast ratios.

TV Types:
There are three TV types

-Direct View: The most common form, they do not project images. You directly view the image from its source. LCD, Plasma, and CRT all come in direct view.

-Rear Projection: This type uses a projector to project an image onto a screen from behind it. These were the original "big screen" TVs and they're still common today. They're bulkier than the alternatives but can offer larger screens, especially with CRT variants. There are LCD, DLP, and CRT projection TVs available. They contain a light bulb to amplify the image. The bulb may need to be replaced infrequently. CRT and DLP are the best to buy as they offer the best image quality.

-Front Projection: These are your traditional movie projector. They project an image onto a traditional movie screen or wall from in front of it. They offer a huge advantage in that they can produce very large images, up to the size of an entire wall in the average home. They can be easily mounted on a ceiling so they're completely out of the way. Of course, the obvious disadvantage is that the image path must be free of obstacles, requiring an uncluttered space. The room must be relatively dark as well. These units also tend to be more expensive. DLP is the best technology to use. CRT projectors are uncommon and are more bulky. LCD ones have a "screen door" effect. DLP are generally the best type of front projection TV to use for home theaters.

HDTV on the Cheap:
Now say you want an HDTV unit in a small bedroom but you don't want to buy an $1000 HDTV. Computer monitors can double as HDTVs. They're relatively small and inexpensive. A decent 19'' one can be bought for around $200-$250. They require a set top box since they don't have a built in tuner. The box must also have either a VGA, DVI, or HDMI port on it to interface with the monitor.
Widescreen computer monitors come in a 16:10 aspect ratio but can display 16:9. They come in resolutions of 900p or 1050p. They cannot display true HD but they're closer. A good monitor will resize the image so it's not distorted when displayed. There are widescreen 16:9 computer monitors out there that can display up to 1600p but these are more expensive. Only computers can display that resolution.

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