Advantage of 1080p vs 1080i for 24fps movies

[pthierry]

Hello everybody,

I see a lot of discussion about the advantage (or lack of) of 1080p versus 1080i, especially for moving pictures.

I was wondering, knowing that probably a lot of the original content for Blu-Ray discs will be movies shot at 24 fps (and played at 25fps), what would be the added value of a transfer into the 1080/50p format instead of 1080/50i ? The two half-frames in the interlaced mode would have anyway the same temporal content, defeating the argument in favor of 1080p, isn't it ?

Also, in case of 1080/50p, how can 50 full frames be generated from a movie containing 25 frames per seconds ? Either a frame out of two has the same content as the previous one, or the content of those additional frames is "invented" by some interpolation, but anyway does not correspond to anything present in the original material.

So, does 1080/50p make any sense for most movies ?

Thanks to give your opinion about this topic...

[Deciazulado]

Maybe this answer i gave on one of the other forums might be of help:

https://forum.blu-ray.com/showthread...7531#post17531

[AV_Integrated]

1080i/50 vs. 1080p/50 should produce ZERO difference on most displays. Obviously, this is only in PAL regions and does not hold exactly true for NTSC regions which operate at 60hz instead of 50hz. I believe in PAL land, one extra frame out of every 24 frames is repeated to make 25 frames, then every frame is shown twice. It may be possible that one frame is shown 3 times and the next frame is shown 3 times to deal with 24fps, but I'm not as sure about PAL 24fps -> 25fps as I am with NTSC 2:3 conversion.

Now, in NTSC land, 60 frames does not properly equate with 24fps. So, the real creme-de-la-creme is a player that outputs at 1080p/24. A true 24 frames per second! Then instead of using a projector that can only handle 1080p/60, you use a setup that allows for 1080p/24 input and you watch the movie at a true 24hz or multiple thereof.

The problem with anything not matching up perfectly (like 50hz in PAL regions) is that you have some mild to serious artifacting that goes on due to the frame rates and the need for frames to be repeated at inconsistent variables. This may slightly stagger motion and is called judder.

Either way - 1080i/60 or 1080p/60 with a display that can operate at 24hz (or a multiple thereof) could potentially recognize the 24fps and display it 100% accurately. The key with both is that all frames are fully presented.

[Psiweaver]

I think there are some digital cinema projectors that can truly display 24fps though i'm not 100% sure about that.

[Ascended_Saiyan]

The Sony VPL-VW50 can do just that.

[AV_Integrated]

The Sony operates at 96hz with 24hz material which is a direct multiple, so it functionally is no different than if it was 24hz.

Digital projectors operating at multiples of 24hz doesn't make sense to me, but I guess there is a reason for it that has yet to be explained fully to me.

The Optoma HD81 is also supposed to be capable of 24hz source and display at 48hz.

[pthierry]

In Europe, 24 fps to 25 fps is simply achieved by playing the movie slightly faster.

[AV_Integrated]

Originally Posted by pthierry

In Europe, 24 fps to 25 fps is simply achieved by playing the movie slightly faster.

Hmmm... that's right isn't it? An entire movie is 4% shorter in length because of the encoding. I'm not nearly as well versed on PAL as I am on NTSC. So, they show the full 24 frames, but instead of using a full second to show 24 frames, like in a theater, you get those 24 frames in 24/25ths of a second. Then they start the next sequence of 24 frames. The speed up is apparently not noticable to most people... I can't say.

[Knight-Errant]

Originally Posted by AV_Integrated

Hmmm... that's right isn't it? An entire movie is 4% shorter in length because of the encoding. I'm not nearly as well versed on PAL as I am on NTSC. So, they show the full 24 frames, but instead of using a full second to show 24 frames, like in a theater, you get those 24 frames in 24/25ths of a second. Then they start the next sequence of 24 frames. The speed up is apparently not noticable to most people... I can't say.

Speaking for myself, I can detect it. I buy american material in region 1 for that reason.

[Deciazulado]

Originally Posted by AV_Integrated

So, they show the full 24 frames, but instead of using a full second to show 24 frames, like in a theater, you get those 24 frames in 24/25ths of a second. Then they start the next sequence of 24 frames. The speed up is apparently not noticable to most people.

Yes that's a good way to put it. The visual speed-up is very hard to tell. Probably if you're not used to watching the film at the correct speed you won't notice. 25fps projection just looks slightly more live than regular 24fps projection. 30fps (Oklahoma!) starts to look noticeably better and different.

I'm still left wondering if PAL region Blu-rays discs will have theatrical films running and encoded at 25fps, or maybe the player's chips can either convert or speed them up on the fly? I have a very cheap ($50) DVD player that does the former, and computer software DVD players do that all the time. And I think at least one of those (WinDVD?) is also capable of speed up/down manipulation.


Going back to the 1080i vs 1080p, IMO I still say that unless everything in the mastering-reproduction-playback chain is implemented correctly it'll be most likely than not that we will not get full 1080p sharpness visible on the display. There are many steps where the full vertical resolution can be lost before it reaches the 1080 LCD pixels, incorrect deinterlacing just being one of them, the first one being at the transfering stage itself!