120Hz and True 24p (1 Viewer)

[troy evans]

This talk of frame rates is very interesting. I just keep coming back to the whole "looks like it was shot with a camcorder" thing. If movies start using higher frame rates as a standard in the future, it damn sure won't look like what's happening on these tvs with 120hz on. It's effect has degraded the image rather than improving upon it.

 

[Jeff Gatie]

Man, we aren't going to have one of those stupid "the director would have shot it in full color 3D hologram in 12.1 surround sound if it existed in 1941, so I want Casablanca to be colorized 3D in 12.1 surround" threads? I thought this was the HTF? :frowning:

By the way, the posters who said the frame interpolation feature is separate from the 120Hz feature are correct. The interpolation can be turned off (as it should be) and you can have just the 120Hz refresh rate (i.e. 24p x 5).

 

[Carlo_M]

Which leads me to an interesting question. Without the frame interpolation (which I'll assume is what creates the "unreality" look to things), then what really is the difference between 120hz (24fps x 5 each frame) and 24fps?

I ask because what people are calling as judder (which may or may not be the right term for it) for 24fps sources is presumably the "missing data" between frames. i.e. each frame accounts for 1/24 of a second, and something in motion does something in the time between 24ths of a second. So we have something like this:

1 - 2 - 3 - 4 - 5

With the theory being the judder is the missing information between 1 and 2, 2 and 3, 3 and 4, and 4 and 5 right? Frame interpolation is meant to fill in that gap so you get something like (roughly):

1 - 1.5 - 2 - 2.5 - 3 - 3.5 - 4 - 4.5 - 5

With the ".5" parts being interpolated and filled in by the processor to give a "smoother" look to it all. That's the "unreality" part of it that bugs most of us.

However true 120Hz with no interpolation would yield this (at 5x the speed of 24fps):

1-1-1-1-1-2-2-2-2-2-3-3-3-3-3-4-4-4-4-4-5-5-5-5-5

So the in-between data, the ".5" are still missing. So what would be the visible benefit to this? Just curious.

 

[Jeff Gatie]

The thing to realize is that since 120 is a multiple of 24, the actual fps will map exactly to the refresh rate:

1-1-1-1-1-2-2-2-2-2-3-3-3-3-3-4-4-4-4-4-5-5-5-5-5 @120Hz

This is in contrast to a 60Hz set, which will give you:

1-1-1-2-2-3-3-3-4-4-5-5-5-6-6 @ 60Hz

Since the 24fps maps exactly to the 120Hz refresh rate, the image is more representative of the actual film look than the 3:2 cadence needed to map 24fps to 60Hz. The benefit is not in the interpolation (Blech!), but in the superiority of a 120Hz display over the old 60Hz displays in displaying a true 24Hz film rate.

 

[ManW_TheUncool]

Agreed, if such displays actually allow this frame quintupling, instead of interpolation, at 120fps.

Also, depending on exactly how the display tech works out, running at higher frame rate like this can reduce the strobe effect. This should be the case for CRT-based displays, but I'm not sure about others like plasma, LCD, DLP, etc. since they don't have the same kind of image scanning issue.

BTW, I thought modern day theaters don't generally actually project at 24fps anymore, but at some multiple of 24fps for exactly that reason.

_Man_

 

[Carlo_M]

Agreed on both counts above. I can see how 120hz being a multiple of 24 reduces the 3:2 pulldown effect on 60hz displays. But it shouldn't result in that look that frame interpolation gives, right? That stuff makes things look "hyper-real" or "unreal" in a way that simple 5x multiplier would do since effectively it's still 24fps of unique information, just shown 5x.

 

[Allan Jayne]

24 fps source to 120 Hz TV set -- Should display with 5-5 pulldown if no interpolation is included.

60 fps 3-2 pulldown source to 120 Hz TV set -- Should display with 5-5 pulldown if no interpolation is included although some models give you 6-4 pulldown. The latter means that all of the 3-2 pulldown judder is still there.

60 fps 720p or 30 fps 1080i to 120 Hz TV set -- Should display with 2-2 pulldown if no interpolation is included. Interlaced material needs to be de-interlaced and not have individual fields used twice in a row as 2-2 pulldown.

30 fps non-interlaced video -- Blu-Ray player will impart 2-2 pulldown and output as 720p, 1080i, or 1080p. 120 Hz TV should impart 2-2 pulldown again with the result being 4-4 pulldown relative to the source.

 

[troy evans]

Thanks Allan, that made it very clear to me. So the effect we see on these displays is more the fault of a "tru-motion enhancement" rather than 120hz? That's what I originally thought was happening, but, wasn't sure.

 

[Sanjay Gupta]

There is a very interesting article on projectorcentral.com called, 'The Big Judder Problem and the Overhyping of 24p'.

 

[AmusingistheDawn]

Interesting discussion here. I happen to be in search of a new television and had been considering samsung's LCD line. I was looking at the series 6 46" because it had the 120Hz feature...and it was a considerable amount more for the series 6, whereas the line right under it only has 60hz, but is a bit more affordable by a couple hundred dollars.

Would it make more sense to deal with the 60Hz and pay less in order to afford a larger television...i.e. 52"?

 

[Reagan]

A quick comment. Some 120hz displays actually do shows a given frame (from a 24fps source) five times. Thus, whatever judder is in the original film will be present on screen at home - no more, no less. Other 120hz displays are not displaying a frame five times, but rather, do other stuff. As that is the limit of my specific knowledge, I'll leave it at that.

As for the Sony's, they have an option called 'motion enhancer' which, when turned on, does not display a frame five times.

Somewhere there's a list of display devicies that correctly display a 24fps source in a multiple of 24 (e.g., 96 or 120 hz) in 1080p.

-R

 

[Jon Lidolt]

They still shoot films at 24 fps simply because the industry is too cheap to spend more money on film prints. The original Todd-AO process goosed the frame rate up to 30 fps (only for the first two Todd-AO productions) and the little seen Showscan process was shot at 60 fps to eliminate strobing entirely.

 

[Sanjay Gupta]

I think the NO. 1 reason for films still being shot at 24fps, is simply the hundreds of thousands of movie theaters accross the world that would have to replace the projectors. Eventually the projectors will get replaced to digital ones and I am sure the industry at some point will then start shooting films at either 30fps or 60fps. Personally I can't wait for this change to happen. I see absolutely no artisitic merit in the judder that comes with shooting at 24fps.

 

[Stephen_J_H]

I used to work projection at a multiplex. Each projector was equipped with a power "rectifier" to reduce the strobe effect, but judder was till visible, moreso on horizontal pans than vertical pans.

 

[ManW_TheUncool]

IMHO, unless you plan to play *lots* of video games on the TV in a brightly lit room or leave still graphics and such on it for hours on end (again in brightly lit room), you're better off buying into some other kind of technology instead of LCD. Get a plasma, if you want a flat panel. Get a DLP RPTV, if you want bigger size for less $ (and don't mind the extra 12" depth), especially if your room isn't showroom floor brite.

_Man_

 

[AmusingistheDawn]

Are you sure? I'm not really into plasmas...I just never really liked them compared to LCD's...I dunno what it is, but it's just something that appeals to my eye. This is all $ for $ too. As far as DLP is concerned...will the picture be any different? I find the price difference to be a bit large to consider the fact that they might look the same. I'm open to suggestions though, as I'm still on the hunt.

 

[Stephen_J_H]

DLP is gorgeous. One of its major selling points is the lack of motion trails that sometimes occur with LCDs and plasmas, though I must say that my 27" 4:3 CRT has worse motion trails than either my 26" 16:9 CRT or my 32" LCD. Go figure.

 

[AmusingistheDawn]

For just about $1500 on amazon, they have samsung's DLP 61" with LED. Think I should just go for it, or wait until Black Friday? That's a pretty good price right now.

 

[professor]

120hz makes film look like video because our brains process images at the equivalent of 60hz. Film has traditionally had that "dreamy" look because it is shot at 24 frames per second. This introduces motion blur, since many things in life move faster than 24 frames per second can capture as a still image. Interestingly, wheels that seem to rotate in the opposite direction do so because they are rotating at the equivalent of 60hz. When the car or wagon slows down, the wheels suddenly seem to spin in the right direction because they are now below 60hz. When your computer monitor's refresh rate is set below 60 hz you might see flickering and get headaches because your brain sees the screen constantly refreshing. Anyway, the reason 120hz TV's make film look like "ultra-video" is because of the rate at which your brain is hard wired to process images. It really has very little to do with telecine pull-down. I will never buy a 120hz TV because it ruins movies for me. 120hz is not the way movies are projected in theatres. I just saw "Speed" at 120hz and I honestly thought at first it was a "behind the scenes" documentary they had made. When I found out it was the actual movie, I was turned off.

 

[professor]

Motion trails because of response time are completely different from refresh rate. If a film is shot at 24 frames per second, it WILL have motion blur. That is natural and desirable. Many things in life move faster than the equivalent of 24fps. That motion blur is permanently etched into the source film and nothing can get rid of it. What 120hz does is interpolates that 24 frame per second source material to artificially create an image that will refresh at 120hz. You still have the motion blur that was in the source film, but now frames are getting repeated and artificially created to hit that refresh rate. Response time is when the LED can't turn on or off or switch colors fast enough. This problem is totally due to the physics of LED's. LED's physically cannot keep up with the refresh rate. When there is no motion on screen, we don't notice that the LED can't keep up because each pixel is the same color it was the moment before. When the motion changes suddenly however, then we see the lag. DLP doesn't have this problem because the mirrors can rotate far faster than the source material's refresh rate.