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!

[Blue]

There is a Blu ray standard for this. It's 24fps. Movies no longer need to speed up or chopped up to fit 25fps (PAL) or 30 fps (NTSC). Although there are still remnants in HD reflecting PAL and NTSC fps the standards allow for both, so a HD TV in the US can play a 1080i/50 form the UK and vica versa. At last movies can be sent around the world (all countries that have adopted the HD standards) an played that is excluding Digital Rights Management e.g. regional encoding.

[Psiweaver]

I find that I prefer the 24fps look to the 30 fps look and so i'm very happy that this is part of the blu-ray standard. When conversion is required IMO 3:3 looks much better than 2:3

[Deciazulado]

Originally Posted by Psiweaver

I find that I prefer the 24fps look to the 30 fps look and so i'm very happy that this is part of the blu-ray standard. When conversion is required IMO 3:3 looks much better than 2:3

Hoping I don't sound too anal but NTSC playback which is what you are refering to when watching 24fps material on 60Hz displays, is not the 30fps look. NTSC is not really 30fps, it's 60i (intelaced fields) so when you watch 24fps material on a interlaced CRT the frames are not repeated, it's "half" frames that are repeated 3:2 (worse, you get to see venetian blinds for a split second), and deinterlaced on a progressive display (LCD, DLP, SXRD etc), then, even tho you get whole frames at last, they are in the 3:2 pattern which is what you meant, but THAT's not the same as film filmed and displayed at 30fps.


Film 30fps is a different beast, used for the Oklahoma! 70mm TODD-AO (30fps) version (best seen IMO on the 4:3 letterboxed NTSC DVD, not the newer blurrier 16:9 coded one ) and some animation programs, animé OVAs, TV SFXs, and commercials.

24 to 60 3:2 has this jerkiness from the frames repeating alternatively 2 or 3 times and as you say, a 3:3 frame repeat at the very least (72Hz), is needed. While true 30fps to 60 looks very smooth and fluid and realistic. Almost live but not quite, still kind of "filmic". Well there's been talk of future 120 Hz displays that would take care of this, displaying 24p, 30p, and 60i videotaped material optimally (5,4,and 2 repeats per frame, respectively). (Good, for example, for Buffy first seasons or Star Trek: Next Generation, etc). Playback of 25p and 50i material would still have some frame repeats but at 120Hz the visibility would be much less and maybe good enough to not matter much.

Just trying to be as clear as possible

Of course if you meant film shot at 24fps looks better to you than film shot at 30 cus it has a dreamy quality on it's movement, pay no attention to me