720p vs 1080i
Dear Gary: I am planning on buying a new TV. However I have not seen much information on whether 1080i is better than 720p or vice-versa. I would suspect 720p is better, but when I look in the local electronics stores, most of the HD-capable TVs do not support 720p. Worst of all I just read that certain broadcast stations have chosen 1080i while others have chosen 720p. On top of that some TVs will downconvert 720p to a 480p image. It is enough to make a consumer SCREAM!! Can you provide some insight on the matter? Ken Ng, a-ken@microsoft.com
Ken Ng
Video Technical Editor Greg Rogers Comments:
Debating the superiority of 1080i vs. 720p is much like arguing the merits of Microsoft Windows vs Apple MacOS. There are good arguments on each side of the debate, and both formats have passionate supporters. Which format is better depends a great deal on what you are trying to accomplish. From a picture quality point of view, 1080i has more than twice the static spatial resolution of 720p. The 1080i format (1920 x 1080) has over 2 million pixels per frame, while 720p (1280 x 720) has less than 1 million pixels per frame. The higher spatial resolution of 1080i is a tremendous advantage when viewing pictures with a great deal of detail and relatively little motion. But the dynamic resolution of 1080i is limited by its field structure (1920 x 540), rather than its frame structure. While 1080i still has superior horizontal resolution, it has less dynamic vertical resolution than 720p. Images in motion are subject to line twitter, image combing, and other interlace artifacts. Fortunately, interlace artifacts are more difficult to see on 1080i than standard-definition interlaced video because there are many more scan lines per frame. Nevertheless, fast action sports are better served by the 60 Hz progressive frame rate of 720p. TV manufacturers have favored 1080i over 720p because the horizontal scan rate required for 1080i (33.75 kHz) is only slightly higher than 480p (31.5 kHz). This makes it less expensive to provide 480p and 1080i in a CRT based TV, than to provide 480p and 720p (45 kHz). More rear-projectors with 720p capability will appear as new high-definition displays are designed with 16:9 1280 x 720 DLP devices. I would like to see all consumer display products be capable of a wide range of display formats and scan rates, as most front projectors are now. This would allow broadcasters and other content providers to use their best technology and select the format most suited to the content they are delivering. It would also encourage scalers and other processors to produce 72 Hz frame rates for movies, which would eliminate the unnatural 3:2 pulldown judder we currently suffer with 60 Hz frame rates.
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