High Definition Video (HD)

HD is actually a combination of different technologies: digital television, advanced pixel resolution and broadcasting that result in a true HDTV picture. With HDTV, images and sound are processed using the same digital code found in computers. The result is a picture with much sharper detail and more vibrant colors. But what transforms any HD television receiver into HD is the broadcast signal and the compression technology used to deliver it.

So how does it work?

There's more to HDTV than just transmitting the image in digital code. The cleaner, sharper image is also due to the size of the pixels. The images you see on standard televisions are made up of tiny rectangular dots, also called pixels. HDTV programs too are made up of pixels, but instead of rectangular dots, they are square. More importantly, they are 4.5 times smaller. This means you're getting  at least four times more detail - so it's almost like comparing printouts from an old dot matrix printer to a laser printer. The other big difference is the actual number of pixels on the screen. On a standard digital TV or analog TV, you are seeing 480 pixels. The minimum amount of pixels on an HDTV is 720, and when you take into consideration their smaller size, it works out to 600,000 more pixels per screen. No wonder the images are so crisp!

Screen Size?

This is sometimes also referred to as the Aspect Ratio. A standard definition TV always has a 4:3 screen size. This is basically a square. 4  horizontal units by 3 vertical units.

All HDTV’s have a 16:9 screen size. This is basically a rectangle. 16 horizontal units by 9 vertical units. It is meant to be configured more like a movie screen to allow the inclusion of more wide and panoramic shots.
 
What do all the 720p vs. 1080i numbers mean?

The world of HDTV is filled with acronyms and numbers. The good news is you don't have to be a techno-geek to begin to understand them. The most common numbers you'll come across, and probably the most important, relate to pixels or the number of lines on a screen. 720p or 720 lines is the minimum HD format and is generally acceptable unless you're planning to purchase an extremely large set.

So, what's the basic difference between 1080i and 720p?

Visibly, you won't see much difference unless you have a large screen TV, but the difference does exist. On standard definition systems, TV images are created by interlace scanning. In other words, broadcasters alternate horizontal scanning lines to create the image. Because they interlace 480 lines in total, the process is called 480i. HD transmissions sent using 1080i, interlace images by scanning more than double the lines, giving you a much crisper image. The other type of HD processing is known as progressive or “p”.

With progressive imaging or 720p broadcasts, the images are scanned from left to right like a computer monitor, eliminating the lines altogether. It's hard to say which format is better. Action scenes may tend to look smoother with progressive scanning, but overall resolution is considered better with interlaced scanning.

Want more Information on HDTV?

http://en.wikipedia.org/wiki/High-definition_television