What is the Difference Between 720p and 1080i HDTV?

   If you're a consumer looking for a new TV, you can easily ignore the 720p vs 1080i debate because every TV which is described as HDTV or HDTV Ready is required to support both formats. Be aware that lots of TVs which support 1080i have fewer than 1080 lines so they scale the 1080 signal down.

   That's not a huge concern as scaled down 1080i is far superior to a regular NTSC signal. It is worth bearing in mind that more expensive HDTVs tend to have better scalers than cheaper ones, and this may be something to keep in mind. However, for broadcasters it's a live issue. Should they broadcast 1080 lines of interlaced video or 720 lines of progressive scan? They could just broadcast two signals, one in each format, but that would use up a huge chunk of bandwidth and be more expensive.

   What is the difference between 720p and 1080i? A 720p signal is made up of 720 horizontal lines where each frame is displayed on-screen for 1/30th of a second. This is known as progressive scan (commonly known as 'p')The quality is like watching 30 photographic images a second on a TV screen.

   A 1080i signal consists of 1080 horizontal lines but only half are displayed on-screen at any given time. The lines are interlaced (known as 'i'), ie every other line is displayed for 1/60th of a second and then the alternate lines are displayed for 1/60th of a second. So, the frame rate is still 30 frames per second, but each frame is split into two fields which the brain then puts back together subconsciously. Most of the time interlacing works fine but fast moving images such as fast moving sports can cause problems. These can show up as a 'stepping' effect on-screen.

   Progressive scan signals don't have this problem and are better suited for sports programs. The line-by-line basis of progressive scan technology captures the inherent fast action of sports much better. The 720p vs 1080i is not a debate worth worrying about. Focus on more important things on your list when you consider your next HDTV purchase.

About the Author

Mike Labram is a home theater enthusiast and owner/webmaster of The Wired Gazette which offers informative home theater tips, articles and reviews for newbies and pros.

This article is the property of Mike Labram and is only allowed to be reproduced with the resource box included.

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