50fps question

[madhatter300871]

I have re-encoded one of my blurays using avisynth interframe (which uses SVP plugins). The results are amazing. Very fluid and very sharp.

My question is, why do we perceive the image to be sharper, how does that effect work on the eye (I am just interested). I am not sure if I like the result, even though I state it is amazing, as I seem to suffer from not liking the soap opera effect. Time will tell if it's for me.

[Didée]

Why does it appear "sharper"? - Re-visit an older thread (http://forum.doom9.org/showthread.php?p=1563441#post1563441). (BTW, you were in that thread, too ...:) )
(If you speak German, follow the link given there. My english explanation in that thread is just awful.:eek: Written in too much a hurry.)

Want to reduce film judder, but don't like soap opera? - Then don't do just [25]-->[50].
- Instead, do [25]-->[75] .SelectEvery(3,0,1) //or// [25]-->[100] .SelectEvery(4,0,1)

Result is not water-fluid like full interpolation, but film judder is vastly reduced, (with some minor judder still being present so it still looks like "film"), and as a consequence, vastly less of the soapy appearance.

This is, BTW, pretty much what modern TV sets with good motion-magic are doing, when they offer a "strength" setting for their motion-magic. Don't interpolate the "full" distance, but just a fraction. So easy. So effective.

[madhatter300871]

I revisited the old thread ...... yes, I was a part of it and it never occurred to me to read it ! Thanks for re-directing me back to it :D

I think I'll try your "selectevery" method next, see how I get on with that. Obviously I will see the result when I try it but right now I don't understand how it would work (although clearly it does). Take the selectervery 4,0,1 method, am I not just selecting the first 2 frames from each group of 4 ? Also, which method do you use to go from 25 to 100, do you use interframe ? I am missing the point here by a mile aren't I !

[Didée]

I don't actually use Interframe or SVP. For the occasional PC-usage I'm okay with regular MVTools-in-ffdshow, (and I don't like SVP to always make my ffdshow script go Nirvana:devil:). - But generally, I just let my TV set do the interframe calculations - much easier, and if you happen to have a halfway-recent S*ny or S*msung, they do better work than any of the stuck-years-back MVTools-base.

For what is happening there, imaging a 25fps film on a 50Hz display. Played natively, every frame is displayed twice. I.e every 2nd frame has moved 0% in relation to the previous one. When doing full interpolation, then every 2nd frame shows motion states exactly in the middle between prev & next frame, i.e. the frame has moved 50%. This is, basically, as if the 25fps film would have been shot with a 50fps camera from the start. Quite smooth, but looks like video, not like film anymore.
The trick with reduced-interpolation is that the inter-frames are not showing objects having travelled the "full distance", but only a fractional distance. When compensating the full distance, it looks like video. Compensating a null distance (native film) causes judder because each frame is displayed too long at one spot, while the eye is moving along. Reduced interpolation reduces the judder because it makes the inter-frames move a little. But avoids video-look because inter-frames don't move the full distance.

However, for the concept to work out "easily", you really need to do "integral" fps upsampling. That's fine with 25->50fps, and modern TV sets can use a variety of refresh rates to make it "fit" (basically: 100/200 Hz for PAL content, 120/240Hz for NTSC/FILM content.)

The most poor situation is when you have 24Hz film, and are sitting in front of a 60Hz-limited PC monitor. Integral fps upsampling is not possible here.

[IanB]

The most poor situation is when you have 24Hz film, and are sitting in front of a 60Hz-limited PC monitor. Integral fps upsampling is not possible here.
[24]-->[240] .SelectEvery(8,0,4) 60p max soapy appearance
[24]-->[240] .SelectEvery(8,0,3) 30%
[24]-->[240] .SelectEvery(8,0,2) 20%
[24]-->[240] .SelectEvery(8,0,1) 10%

Downside, 4 of 5 output frames are interpolated, the 1 of 5 original is only every 2nd input frame.

[Didée]

That's right, of course you can construct the same motion-characteristics also in 24->60. What I had in mind, but didn't write about, was
Downside, 4 of 5 output frames are interpolated, the 1 of 5 original is only every 2nd input frame.
From the generalized point of view that interpolated frames "generally contain artifacts", it is much preferable to have an integral framerate ratio for the conversion. clean-artifact-clean-artifact-.... with all original frames being present, is much more forgiving to the eye than clean-artifact-artifact-artifact-artifact-clean-...., with every 2nd original frame not being present anymore.

And that's why 24->60 is the poorest situation. It would be a different story if the display can do eg. 72 Hz, or 96 or 120 Hz.
Another compromise would be to go with sth. like
A (20%) (80%) B (40%), by [24]->[120] .selectevery(10,0,1,4,5,7)

But anyway, hands down: if it's about movie experience, a PC monitor isn't quite up to the task.

[wonkey_monkey]

Don't interpolate the "full" distance, but just a fraction. So easy. So effective.

I'm surprised it doesn't actually look awful. Small motion in one frame, large motion in next... why doesn't that look really terrible? (assuming that is what my TV is doing with its judder reduction strength slider).

David

[Didée]

At the first thought, it might be somewhat against the guts, sure. But the more you think about it, the more it makes sense. And the more you look at it, the more it makes sense. :)

Example: 25fps progressive, displayed on a 100Hz panel. Darkblue = orig frame (and 2:2 pull frame), light blue = filler frames

1) Vanilla presentation. No motion compensation.
http://thumbnails107.imagebam.com/23325/860f74233249330.jpg (http://www.imagebam.com/image/860f74233249330)
Full 25Hz phase boundaries. Full Judder.


2) Interframes at maximum "strength"
http://thumbnails101.imagebam.com/23325/177504233249311.jpg (http://www.imagebam.com/image/177504233249311)
Smooth like water. 25Hz phase boundaries have completely vanished. Doesn't look like film anymore. Soap / video effect.


3) Interframes at 50% "strength"
http://thumbnails101.imagebam.com/23325/5f95e3233249298.jpg (http://www.imagebam.com/image/5f95e3233249298)
Judder reduced, because frames are tracked a little. 25Hz phase boundaries still present. Still looks like film, mostly.

[madhatter300871]

Fascinating !

I haven't had a chance to do anything over the last few days but I will be trying this out one evening this week. I live in PAL land and am working with a 50Hz LCD display, both my TV and projector. I haven't splashed out on a 100Hz set yet, and to be honest now that I have realised that I don't like the soap opera effect I am glad I haven't.

I now understand about the selectevery method talked about here and am going to have a play with it.

On a side note, the penny has now dropped regarding something I saw in the TV department of a high street shop. There was a fantastic Panasonic flat screen TV on display, big and thin. Avatar was playing. It was like watching "the making of Avatar". It actually looked like the people where inside cardboard spaceships and everything looked really fake. I couldn't work out why, or if I was indeed watching the making off. Now I realise, I'll bet money it was a 100Hz or even 200Hz display and what I was seeing was the effect of frame interpolation. I'll admit it was razor sharp, quite amazing actually, but for me at least was a very poor movie experience.

[2Bdecided]

I think you misunderstand.

Plenty of 100fps and 200fps displays keep film looking exactly like film (or pretty much like film, as Didée suggests), while using motion interpolation to reduce motion blur on 50i/60i content (which should be smooth, but appears far more blurred on 50fps LCDs than on the 50fps CRTs it was designed for).

Some 100fps displays apply full motion interpolation to 24/25fps content, but not all. Most can have this turned off (or down).

Some only have fully on / fully off options (and with fully off, even 50i looks bad - meaning "ideally" you have to switch manually between 25p and 50i), but by no means all operate in this way.

Cheers,
David.

[madhatter300871]

No, I'm pretty sure I understand now. What I saw with the Avatar demo was the effect of interpolation, on that I am now sure. I take on board your point about being able to turn down motion interpolation setting.

However, on my 50Hz LCD television, and my projector also, interpolating to 50fps makes a massive difference and all I have to do now is play with the selectevery method to see if I can achieve a result more pleasing to my eye.

I'm still not convinced that I will be upgrading to 100Hz any time soon, even you say that on some 100Hz TVs with interpolation turned fully off the picture looks bad. I would be gutted if I picked one of the TVs that didn't do a good job.