All About High Definition Television

High Definition in general refers to the resolution of an image. To understand the High Definition Television(HDTV), you'll have to get comfortable with the term "Resolution". It is lot easier to understand resolution using the concept of lines and grids. In simple terms, let's assume that the TV screen you have is divided by horizontal and vertical lines. Smallest intersectional area on such a screen is known as "pixel". Now what is pixel? A pixel is the smallest cross-sectional area of an image and it is known as the unit of resolution. For example, if you measure length in centimeters (cm), then cm is the unit of length. In same way, resolution is measured in pixels and thus pixel is a unit of resolution.

There are multiple resolutions currently in use.

First number represents number of horizontal lines or pixels while second number represents vertical lines or pixels. For example, 1920X1080 resolution is a screen divided by 1920 horizontal lines and 1080 vertical lines.

Now how much more details are contained in a High Definition picture compared to a standard television. Our regular NTSC TV picture is scanned using 525 lines, while HDTV uses 1125 lines to scan a image. In term of quality and details, just by doubling the number of lines in HDTV, it contains 5 times more details about the picture. Take a look at the images below and you’ll understand what high resolution actually means.

Technically all three images are displaying same content. All three images are divided into small sections by horizontal and vertical lines. Let’s assume that the smallest area each image can show is the cross-sectional area(this is called pixel in technical term). Obviously, there are more horizontal and vertical lines in the image on the far right. So it can show you more pixels and thus it has higher resolution. So for the same screen size, more the number of pixels, better is the resolution.

Now going back to our original resolution data. If we have same screen size, a resolution of 1920 by 1080 lines will produce lot more pixels than 1280 by 720 lines.

So in theory, 1080 resolution has 2.25 times more pixels than 720 and thus far better resolution. In current standards, 720p is considered a true HDTV resolution. So any set with 720p or higher resolution will be considered a true HDTV set. Further, HDTV transmission not only has more video details, it also includes 5.1 channels of Dolby Digital audio.

Between HDTV and old Analog TV, there is another format in existence and it is called EDTV(Extended definition TV). This format relates to 852X480 scan lines.

Here is another important fact to remember. Having a better resolution doesn't mean that you'll see more. Remember, How much you can see in an image will also depend how far it is from your eyes. For example, let’s consider all three images shown in the picture above. All of them are of same size(about 4 cm by 4cm), But the one on the right has highest resolution that is almost 2.25 time higher than the one in the middle. But this higher resolution is meaningless if these images are about 20 meters from your eyes. They are small in size so at that distance you’ll probably see all images as pink dots. So important thing to remember is that resolution matters and so does the viewing distance.

Now let’s move on to those funky alphabets you see after the resolution numbers. For example, 1080i or 1080p. what does that mean?

1080i vs 1080p

Even though there is a big debate on 1080i vs 1080p, It simply indicates the technology being used to refreshed your High Definition picture. In 1080 , "p" means progressive, while "i" means interlaced. With progressive-scan HDTVs designated as 720p and 1080p, screen is refreshed all at once every 1/30th of a second. With interlaced screens, which is what HDTVs labeled 720i and 1080i as well as regular standard-definition TVs are, the odd-numbered scan lines are refreshed first, then the even-numbered lines. So technically only half the screen is refreshed in one pass.

Because progressive scan refreshes the entire screen in a single pass, progressive-scan HDTVs offer a somewhat cleaner, smoother picture, which can help when viewing sports and other fast action videos. But overall, both progressive-scan and interlaced TVs are fine. Another important item to remember is how TV stations broadcast their signals. Some HD signals are broadcast in 1080i while others in 720p. There is no "on the air" 1080p signal at this time. But Blu Ray disc(HD DVD) do have 1080p resolution. Also, Xbox games are coming out in 1080p resolution (Xbox 360 1080p), so if you intend to connect your TV to your video game console, 1080p is the way to go.

If your local station is broadcasting in 720p, does that mean that you need to buy a 720p resolution HDTV to view it? Absolutely not. Your HD set has a native resolution that will override broadcasted resolution. For example, if you local station is broadcasting in 1080i and you bought a HDTV with 720p resolution, your TV will downscale(down convert) the signal and display it is 720p resolution. Same is true for other way around. If transmission is 720p and TV is 1080p, it will upscale (up convert) the signal to 1080p and display. Up scaling will not add any more resolution than what is originally available with the signal.

Most HDTV sets have a aspect ratio of 16:9. That means they measure 16 inches horizontally to every 9 inches vertically. Standard sets are 4:3, or 4 inches horizontally to every 3 inches vertically. HD broadcasts are generally in 16:9, but most non HD broadcasts are still in 4:3. If you watch them using your HD set, you'll see black bars on both sides of the screen. Some HD sets have an option to stretch the 4:3 broadcast and fill up the screen.

Currently there are only two High Definition formats that are being used commercially: 720p and 1080i. However, if you go to your local electronics store, you'll see HDTV with 768p resolution as well(1366X768). Remember there is no 768i/p broadcast format on the air, so your image is going to be re-scaled to fit your screen. This is done using a video processing chip in the display. Obviously there is no future for 1366X768 format. It is just what is available due to chipset and manufacturing boundaries and it is typical for low end LCD and many Plasma technology HD sets.

On the side note, Resolution of a 35mm theater film is 4096 by 2160. So even with the best High definition format today(1920 by1080p), we are no where near a HD resolution of a Movie theater film.