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High Definition Information High Definition Information
What is High Definition?

We all probably understand that High Definition (HD) implies better picture quality, but what does it really mean? High Definition simply refers to a particular size of Screen Resolution. It is as simple as that!


What is Screen Resolution?

Screen Resolution is the number of dots going across your screen by the number of dots going down your screen. This can be further simplified to the number of lines a screen can display. For example, 640 dots x 480 dots (or 480 lines) has 307,200 dots in total. Dots are also commonly called Pixels.

The ratio of the number of pixels across by the number of pixels going down your screen is the Aspect Ratio. There are two main Aspect Ratio's that are widely accepted in the Home Theatre market which is Video format (4:3) and Widescreen format (16:9).

All TV's and Projectors have a native Screen Resolution which is a good measure of the quality of the TV or the Projector. For example, a good quality LCD TV will have a native Screen Resolution of 1366 x 768 or higher and a good quality Projector will have a native Screen Resolution of 1280 x 720 or higher.

There are many native Screen Resolutions :-

Resolution Screen Lines Aspect Ratio Dots or Pixels
320 x 240 240 Video (4:3) 76,800
640 x 480 480 Video (4:3) 307,200
800 x 600 600 Video (4:3) 480,000
1024 x 768 768 Video (4:3) 786,432
1152 x 864 864 Video (4:3) 995,328
1280 x 720 720 Widescreen (16:9) 921,600
1920 x 1080 1080 Widescreen (16:9) 2,073,600

and the list goes on. From the total number of pixels in the above list, it is not hard to see that a resolution of 1080 has more then twice the pixels of a resolution of 720. This means the resolution of 1080 to more then double that of 720, even though we have only added an additional 360 lines of resolution.

When the native Screen Resolution of a TV or Projector is 1280 x 720 or better, then the TV or Projector is High Definition. Otherwise, the TV or Projector is Standard Definition.

Is Screen Resolution enough to ensure good picture quality? The answer is Screen Resolution is only half the story. The other half of the story refers to the resolution of the pictures that are sent to your TV or Projector. We refer to this as Image Resolution.

What is Image Resolution?

Image Resolution refers to the picture size that is sent to your TV or Projector, which can come from a number of different sources, such as, a Set Top Box, a DVD Player, a Home Theatre PC and so on.

There is only a small number of Image Resolutions supported :-

Resolution Screen Lines Aspect Ratio Dots or Pixels Image Type
720 x 480 480 Video (4:3) 345,600 NTSC Analogue TV
720 x 576 576 Video (4:3) 414,720 PAL Analogue TV
1280 x 720 720 Widescreen (16:9) 921,600 HD Digital TV
1920 x 1080 1080 Widescreen (16:9) 2,073,600 HD Digital TV

The above information can also be presented graphically as follows :-


Resolutions outside the above accepted Image Resolutions will have bars added around the picture to make it fit into one of the above resolutions. Typically, the bars will only be added to the top and bottom of the image.

From the above table it is easy to see that a resolution of 1080 has exactly five times more pixels then a resolution of 576 (a PAL Analogue TV signal). We can safely say that a resolution of 1080 is five times better then a PAL Analogue TV signal.

When the Image Resolution is 720 or 1080 then the picture is High Definition. Below that the image is Standard Definition. 480 or 576 is Standard Definition.

Standard Definition vs High Definition Devices?

In order to get the best picture quality, you really want both the Screen Resolution and the Image Resolution to be High Definition. This becomes even more important the bigger the picture you want to watch.

So what happens if you connect a Standard Definition device to a High Definition TV or Projector? The picture will end up being fuzzy as the TV or Projector tries to enlarge the picture to fit the screen. This means hooking up a Standard Definition Set Top Box to a High Definition TV or Projector will result in a poor quality picture! This is why Foxtel, which is a Standard Definition Set Top Box, looks fuzzy on a High Definition TV or Projector.

The same goes for a DVD Player. To get the best picture quality use a High Definition DVD Player, which at the time of writing this article, are just starting to appear on the market. A Standard Definition DVD Player will only output a Standard Definition picture even if the movie is recorded at a higher resolution on the DVD, which is typically the case. If your DVD Player does not have High Definition written on it, it is a Standard Definition DVD Player.

A Home Theatre PC is High Definition by nature. Each High Definition Digital TV card is equivalent to a High definition Set Top Box. All Home Theatre PCs include at least two High Definition Digital TV cards. If you only have a Standard Definition TV and you are not planning on upgrading your TV anytime soon, then you do have the option of purchasing a Home Theatre PC with Standard Definition Analogue TV cards and upgrading at a later date. The Video Card in a Home Theatre PC is responsible for sending the video signal to the TV or Projector. The Video Card in all Home Theatre PCs are High Definition and can support Screen Resolutions far greater then 1080. A Home Theatre PC also includes a DVD Player/Recorder which is also High Definition. For more information on DVD quality, please see our Superbit DVD article.

What is the difference between Full-HD and just HD?

More and more manufactures are using the term Full-HD to represent a Screen Resolution of 1080 and the term HD to represent a Screen Resolution of 720 or 1080 or higher. When a piece of equipment is labelled as Full-HD you can be certain that the native Screen Resolution is 1080, but when a piece of equipment is labelled HD, further investigation is needed to determine the actual native Screen Resolution of the equipment in question, it could be 720 or 1080 or higher.

Manufactures have introduced logos to highlight that a piece of equipment is Full-HD, however, there is no single logo used by all manufactures, they are all different, which can add to the confusion.

Is there anything else that effects picture quality?

There are many factors that can effect picture quality, but choosing equipment that is High Definition is a step in the right direction to ensuring you do get better quality pictures.

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