本文发表在 rolia.net 枫下论坛Regarding 1080i/1080p, it's a very long convoluted process. Here's the theory:

Typical HDTV's operate at 60Hz (meaning the screen 'refreshes' - redraws itself 60 times per second), except the newest TV's which support 120 Hz. Retailers like to advertise 120Hz as having fast fluid motion (like the latest Future Shop ads) - gag! Movies are filmed in 24 frames per second, and typical sports over the tube are sent in 1080i at 30 frames per second.

Since the DVD days, in order to display DVD (and now HD-DVD and Blu-Ray) on TV's and HDTV's, you have to convert the native 24 frames per second video to 60Hz. This process is called "3:2 pulldown." This is important.
----------

What 3:2 pulldown does is convert 24 frames per second film to 30 or 60 frames per second, which is what the TV operates at. In order to do this, it has to do some frame combining. Note I don't know this process exactly, but this is basically the gist of it:

Let's look at the first two frames of a video. Call frame 1 "A" and frame 2 "B" (there's 24 frames per second, so this is 2/24ths of a second).

3:2 pulldown at 60Hz will take Frames A and B and display them in this order: A, A, (A+B), B, B.

Notice that two frames were combined to create a smooth transition from frame A to frame B. Unfortunately, while without this step video would be very jerky, even with it there is some jerkiness, which is often called "judder" or "telecine judder" . A much better read can be found here:

http://en.wikipedia.org/wiki/3:2_pulldown#3:2_pulldown

-----------

Now, after that background, here is how 1080i looks exactly like 1080p on modern TV's:

Since 1080i is interlaced - it transmits half of a 1080p frame, then the other half, here's how it works:

Video is 24 frames per second. TV's work at 60Hz as mentioned before. What the TV does is combine each half of the 1080i signal internally, perform 3:2 pulldown, and voila - a 60 Hz recreated 1080p video is born! Since the video itself is only 24 frames per second, and the TV's redraw 60 times per second, it's not very difficult to recreate a 24 fps image that's trasmitted at 1080i (ie it's transmitted as 48 half frames per second)

Why 120 Hz TV's are so special:

OK so in my previous section I tried to explain to the best of my ability how 1080i is converted to 1080p in modern HDTV's, as well as the jerkiness - judder, that happens by converting 24fps film to 30/60 Hz internally in the TV.

Some new TV's are advertised as 120Hz. What does this mean?

Simple: instead of redrawing the TV 60 times per second, it does it 120 times. Whoopy doo, right - film is only 24 frames per second!

But here's the rub: 120 is a perfect multiple of 24 (120 / 24 = 5). It's also a perfect multiple of 30 (120 / 30 = 4).

Guess what: film currently is either shot in 24 frames per second (DVD, HD media) or 30 frames per second (live TV).

When you have a 120 Hz TV that properly decodes a 24fps DVD/HD-DVD/BluRay, it performs a 5:5 pulldown (yes that's what it's called).

As long as the TV really is 120 Hz, this should, in theory, create absolutely no judder/jerkiness/whatever. Pretty sweet eh? Yeah, "true" 120 Hz TV's should be awesome, and it will be a must-have feature in the future.更多精彩文章及讨论，请光临枫下论坛 rolia.net