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The temporal resolution of HDTV can be higher than CDTV and may be progressive. CDTV - normal, analog TV - is broadcast at 30 interlaced frames per second (fps). The temporal resolution of DTV (SDTV, EDTV and HDTV) can be 24p, 30p, 60i and 60p. Here is the list of temporal variants that all digital TV tuners must support. Many people associate higher temporal resolutions with HDTV, but it is actually a characteristic of DTV - HDTV being a subset of DTV. Most televisions only support interlaced television which draws odd and even lines in separate fields. Here's a drawing from the book that explains how interlaced television works.
The numbers on the right of the diagram are considered odd scan lines and there are 240 of them. The even scan lines are on the left and go from 241 to 480. When these are interlaced or woven together, they form a complete field of 480 scan lines. Progressive is much easier to explain since the scan lines are progressive down the screen. The following table compares the difference in scan lines.
DVDs are shipped with interlaced MPEG-2 video. Progressive scan DVD players use algorithms to create a complete picture and then send the signal to an interlaced progressive scan TV. Progressive scan DVD players won't do much for you if you don't have a television that supports progressive (most televisions still only display interlaced images). HDTV temporal resolution is not always better than CDTV. 1080i has the same 60i (60 interlaced frames per second) temporal format as CDTV. 1080p is often considered the holy grail of video quality since it is 30p (30 progressive frames per second). The ability to see the difference between 30p and 60i depends on the content, the MPEG-2 decoder in your video decoder, and the television set you are watching. The greater temporal resolution usually comes with 720p or even SDTV and EDTV. All three of these formats can be sent at 60p. Depending on your television, this can reduce flicker and make the picture smoother and easy on the eyes. It's difficutl to see the difference between 30p and 60p in action sports because your eye and brain meld much of the information together. The 60p shines though if you show things in slow motion. Another benefit of PVRs is that you might be able to play the video back at half speed and see twice as much information as a 60i video. The problem is that most PVRs don't record at 60p. I don't know if most of the new HDTV PVRs do this or not. I'll keep you updated when I find out. The other big difference with HDTV is that it uses a 16:9 aspect ratio instead of the classic 4:3 aspect ratio of SDTV. TV |
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