Resolutions

Whilst looking for a high definition television you will come across the terms 720p,1080i and 1080p. This refers to the resolution and the type of scanning. The digit is the number of pixels on the vertical. The full resolutions are:

• 720 - 1280x720
• 1080 - 1920x1080

Compare these resolutions to the 720×576 of a CRT (576i in HD terms) and you can see why the pictures on HDTVs are far superior. There are two different types of scanning used, ‘i’ interlacing and ‘p’ progressive.

• 720p - 1280 x 720 progressive scanning
• 1080i - 1920 x 1080 interlaced scanning
• 1080p – 1920 x 1080 progressive scanning

Interlaced Scanning

Interlacing was developed in 1932 for CRTs to receive and display the analogue television signal. It captures an image and displays every other line from left to right and top to bottom. It alternates on the next scan and displays the lines it missed out previously, constantly repeating the process. This technique was invented to save bandwidth and it halved the usage.

Progressive Scanning

With progressive scanning images are captured and are displayed line by line, from left to right and top to bottom. This approach uses double the amount of bandwidth that interlacing does.

Refresh Rate

HDTV refreshes 50 times a second for both interlaced and progressive. A CRT refreshes 25 times a second. So not only in this detail greatly improved but it refreshed twice as much.

Conclusion

The 1080p is the best resolution you can get. Well in theory anyway. The 1080i and the 1080p display the same picture quality, just in different ways. The 1080p displays the full picture at every frame while the 1080i displays half a picture every frame. So is the 1080p worth paying extra cash for? Well you would do amazingly well to be able to tell the difference from a television displaying in 1080p to 1080i.

Sky HD, Virgin Media and Microsoft xbox 360s all support up to 1080i. This means they can output in 720p too. They are unlikely to change to 1080p in the foreseeable future.

Blu-ray and Playstation 3s support 1080p. However, this doesn’t mean you cannot watch Blu-Ray movies or play on Playstation 3 games if your television is not capable of displaying 1080p. They can still display in 1080i and 720p. So it is down to personal choice if you want the extra outlay for a very slight improvement.