Film-Tech Forum ARCHIVE: Are 120hz televisions ideal for 24fps blu ray playback?

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Posted by Cameron Glendinning (Member # 3516) on 05-18-2009, 06:14 PM:

I have been told that 120hz television is ideal for blu ray 24fps playback. Personally my eyes tell me it it looks wrong, Nothing like it did when I ran it at the cinema. Is there any truth in the statment below?

quote:
I'd like to make one comment about the 120 Hz feature. To the best of my knowledge, this feature is meant to display movies at their native frame rate (24 fps) -- exactly as the filmmakers intended it to look. Here's how:

A typical projector updates the image at 60 fps. If you try to show a 24 fps movie on a 60fps video display, each frame of the movie gets displayed for more than one frame of video. At 60 fps:

60 fps / 24 fps = 2.5 video frames per film frame.

Since you can't evenly divide the film frames into the video frames, you have to use a process called "pulldown" to evenly divide the film frames across the video frames. Here's what it looks like:

1 1 2 2 2 3 3 4 4 4

That's 4 frames of film as they are displayed on a 60fps device. Note that frame 1 gets two slots, but frame 2 gets three slots. So each frame of film is not on screen for exactly 1/24 of a second. In fact, frame 1 gets shown for 1/30th of a second and frame 2 gets shown for 1/20th of a second.

So it's not really 24fps. It's flopping between 1/20th and 1/30th as necessary to keep the frames synced and AVERAGING OUT to 24fps.

The beauty of 120Hz technology is that you can divide 24 into 120 evenly:

120 fps / 24 fps = 5 video frames per film frame.

So now your video frames look like this:

1 1 1 1 1 2 2 2 2 2 3 3 3 3 3 4 4 4 4 4

Notice how every frame of film gets exactly 5 frames of video at 120Hz? Guess what -- that's 24fps. EXACTLY. The way the filmmakers intended.

120 Hz technology is often advertised as providing "smoother" motion. This is true -- in smooth panning shots, the 3:2 pulldown process INTRODUCES JUDDER. At 120Hz, the judder does not get introduced, thus it is smoother.

However, 120Hz is NOT meant to add any additional temporal information, and shouldn't make your movies look like 60fps sports/news-casts.

Posted by Joe Redifer (Member # 3) on 05-18-2009, 07:13 PM:

If you see a 120Hz TV on display in a store, it is likely they have the smooth motion or whatever it is called turned on, which interpolates new frames to achieve a fake 60fos or 120fps look and feel. Yes, it looks wrong and quite awful, in my opinion. But with that feature turned off and the Blu-ray player delivering true 24fps material, it should look great.

Posted by John Hawkinson (Member # 1135) on 05-18-2009, 07:20 PM:

Perhaps it looks difference in 50 Hz countries and 60 Hz countries.

--jhawk

Posted by Cameron Glendinning (Member # 3516) on 05-18-2009, 08:45 PM:

John, In Australia we have motion flow 100hz, which looks, well showscan like, similar to how Joe discribes. The quote above comes from an American who is positive it is neccesary.

My own Blu ray and projector will both play and reproduce 24fps, My projector does not feature motion flow.

I am still trying to understand what the hell he is talking about ?

Posted by Bobby Henderson (Member # 840) on 05-18-2009, 08:46 PM:

120Hz HDTV sets always work with a 120Hz refresh rate. But the "motion flow" thing is another feature altogether.

I never use the Motion Enhancer feature in my 52" Sony Bravia XBR4 TV set when playing Blu-ray movies. It makes the movies look strange, like they're sped up and shot on videotape. Plus the interpolation blurs off a lot of image detail. With the feature turned off (as well as a number of other noise reduction and sharpening features turned off) you get Blu-ray playback results that look fairly similar to good 24fps film projection. The imagery is not "judder free," but neither is film projection in a movie theater. The upside is the imagery doesn't have the odd ball 3:2 artifacts common to transferring 24fps material to 30p or 60i fps rates. Since each movie frame is flashed 5 times image quality is dramatically improved over LCD-TV sets with slower refresh rates. The slower ones are more prone to lag and smear issues.

Posted by Julio Roberto (Member # 4976) on 05-19-2009, 07:47 AM:

It's my belief, that a lot of the information in the quotes is not correct.

Most modern TV's and projectors, like computer monitors have done for a long time, are able to NATIVELY display content at whatever (within reason) frame rates they are asked to.

Thus, most modern TV's, will smoothly and perfectly display 23.976, 24, 25, 29.970, 50 and 59.94. The TV will NOT try to convert either one of those frame rates into any other for display. They simply adjust the "scan rate" and "display rate" to match the input.

But recently, TV's have been introduced capable of (much) higher refresh rates, indeed reaching the 120hz or 240hz (or even fake 480hz). These TV's, if you so wish, can try to interpolate motion from whatever frame rate is input(ed?) to whatever other it supports for this function.

I totally agree with the opinions here that the motion interpolation can be and often is awful, and should be switched off most of the time.

I never liked that 100hz motion interpolation we had here for ages and a lot of TV's wouldn't allow you to turn the darned thing off.

Of course, a lot of people like the look of interpolated-motion at higher frame rates (all the way to 240hz!), but you know that what looks or sounds good to some, looks or sound like crap to others.

I would buy a TV with the highest "real" frame rate available (why not, they cost about the same and you could use it for frame-sequential 3D) and make sure that motion interpolation can be switched off. That way you'll watch 24fps at 24fps. No more, no less, no pulldown, no convertion.

Posted by Jim Cassedy (Member # 4115) on 05-19-2009, 09:57 AM:

quote:
process called "pulldown" to evenly divide the film frames across the video frames. Here's what it looks like:
1 1 2 2 2 3 3 4 4 4

Ok, it's been awhile since I've dealt with this and I haven't
had my coffee yet this morning so my brain hasn't fully kicked
in, but I thought at least two of those video frames contained
two film frames to make the math come out even.

(IE: Two of the video frames was composed so that video
field one contained info from film frame 1 and video field
two contained info from film frame two)

The pattern repeated every 4 video frames, and I think
it was referred to as 3:2 pulldown.

Kick me if I'm not awake yet!

Posted by Bobby Henderson (Member # 840) on 05-19-2009, 10:40 AM:

quote: Julio Roberto
Thus, most modern TV's, will smoothly and perfectly display 23.976, 24, 25, 29.970, 50 and 59.94. The TV will NOT try to convert either one of those frame rates into any other for display. They simply adjust the "scan rate" and "display rate" to match the input.

Most television sets have a fixed refresh rate that does not change, even the new 120Hz HDTV sets. In North America the vast majority of TV sets in use operate only at 60Hz. That includes many HDTV monitors, especially LCD-based monitors. Blu-ray players must have their video output settings adjusted for the resolution and refresh rate native to the TV playing the content. A 60Hz HDTV set will not play Blu-ray movies in native 24p mode. The frame rate will be converted via 3:2 pulldown to match the 60Hz refresh rate.

CRT-based computer monitors could adjust refresh rates based on resolution settings that were used. But that's an entirely different application than watching TV.

Posted by Robert Minichino (Member # 3495) on 05-19-2009, 11:06 AM:

As far as I know, the 120Hz sets don't do the 5:5 pulldown as they should, they just do either that stupid interpolation or 3:2 pulldown. So even with a 1080p24 signal going into your set, your set is doing 3:2 for 60Hz, or monkeying with it for 120Hz, and some do 72Hz which is good. If anyone knows of a set that'll do 120Hz with 5:5 I'm listening. [Smile]

Posted by Bobby Henderson (Member # 840) on 05-19-2009, 12:28 PM:

What is your proof 120Hz HDTV sets don't really do 5:5 pull down of 24p material on Blu-ray?

Posted by Julio Roberto (Member # 4976) on 05-19-2009, 01:41 PM:

Ok, just to be clear, what I meant, is that most modern LCD TV's refresh at effective rates that are indistinguishable from the native ones.

If they see a 24fps signal and they can refresh as fast as 48fps, they'll display it at 48fps, wich, w/o motion interpolation, would look exactly the same as 24fps, except the frame change will occurr much faster when it goes to the real next frame, like i.e having a 3 blade shutter as oppossed to a 2 blade shutter, except that there is no blank interval whatsoever and no flicker (unless the TV inserts one for added motion rendition on some models for which it looks better that way).

What I try to say is that no modern LCD TV does 3:2 pulldowns or stuff like that. They may try to do reverse 3:2 pulldown from sources for which the pulldown has already been inserted, but that's a whole different issue and the right way to go, anyway.

A TV that tops out the refresh rate at 120 can also refreah at 100 or 72h or 60hz or 50hz or 96hz, if so desired by the manufacturer (and it's often the case with most LCD TV's in the market today).

Plasma and CRT's are another thing, and in those, native refresh rates may not be so flexible, but often are pretty flexible as well.

If you want to call it pulldown (I call it variable refresh rate), they all do 2:2, 3:3: 4:4, 5:5 or whatever you want so it's an even number from the 23, 24, 25, 29, 30, 50 or 60 input. Basically, the same image remains on the screen all the time until it's the right time to change. Then it's switched for the next one as quick as the panel allows.

So, again, if you have say a 100hz screen, and you input a 24fps signal, the TV will display it 4:4 at 96hz, not at 100hz. If you shoot it a 30fps signal, it will do either 60hz or 90hz (if the manufacturer decided to support that rate). If you shoot it 50fps, it will do 100hz. If you shoot it 60hz signal, it will do 60hz. It will not try to make it an un-even 90hz or 100hz (tops in this example).

LCD's are NOT fixed to a given screen refresh rate. They are just limited to a MAXIMUM screen refresh rate and to those supported by the firmware and drivers, mostly. And nowadays, that includes support for 23,24,25,30,50 & 60 frame rates w/o uneven pulldowns.

http://www.hdtvmagazine.com/articles/2008/01/lcd_specs_playing_with_your_eyes.php

Of course, some older TV's were limited to say 1080i/60 and had to convert to that.

Those times are all but gone with modern LCD TV's. Refresh rate is more a marketing ploy than a real advantage. Of course, the faster the switching speed, the less you can see the motion smear in-between frame changes, but that's pretty small nowadays and many panels with active LED illumination hide it by dimming the screen during the duration of the change over.

Posted by Joe Redifer (Member # 3) on 05-19-2009, 03:37 PM:

quote: Robert Minichino
As far as I know, the 120Hz sets don't do the 5:5 pulldown as they should

Doing 5:5 pulldown is pretty much the entire point of a 120Hz television there, buddy.

quote: Julio Roberto
So, again, if you have say a 100hz screen, and you input a 24fps signal, the TV will display it 4:4 at 96hz, not at 100hz.

No, it won't. 100Hz sets are horrible. I am soooo glad I don't live in PAL land. There is absolutely no reason for 100Hz sets to exist any more.

Posted by Phil Hill (Member # 371) on 05-19-2009, 03:50 PM:

quote: Joe Redifer
I am soooo glad I don't live in PAL land.

Ditto!

Posted by Julio Roberto (Member # 4976) on 05-19-2009, 05:07 PM:

quote: Joe Redifer
No, it won't. 100Hz sets are horrible

It was just an example. With HD 100hz displays are a thing of the past. They already had their 20 years of life span gone. All the new HD TV's anywhere in the world now all support 50hz and 60hz (and 24hz) at least and thus 120hz when they double up. Natively, with no (uneven) pulldowns.

But I'll surely take 100hz any time before a 60hz one with it's here-it-comes-o-no-wait-here-comes-again-o-stop-for-a-moment 3:2 pulldown ...

lol

[beer]

Posted by Bobby Henderson (Member # 840) on 05-19-2009, 09:24 PM:

quote: Julio Roberto
LCD's are NOT fixed to a given screen refresh rate. They are just limited to a MAXIMUM screen refresh rate and to those supported by the firmware and drivers, mostly. And nowadays, that includes support for 23,24,25,30,50 & 60 frame rates w/o uneven pulldowns.

That is not true, and the article you linked from HDTV magazine didn't prove your point either. It did more to describe the limitations of older LCD-TV sets and the optional image interpolation features (motion flow, etc.) the 120Hz TV sets offer.

Most TV sets in North America are bound to a 60Hz refresh rate. Some newer, higher end models offer varying refresh rates, like 60Hz and 96Hz (I think the Pioneer Kuro is one such example). But such TV sets are not common since Blu-ray and HD-DVD were the first consumer video playback formats designed to support native 24fps operation. Some upconverting DVD players as well as high definition disc players can do reverse pull down tricks to make DVD look like 24fps, but 24p was not a natively supported frame rate for DVD.

The playback device (DVD player, Blu-ray player, VHS deck, etc.) is the main thing dictating the frame rate, not the TV set. In the case of older video formats the 60i/30p rates don't change. In the case of PAL in Europe everything is 50i/25p.

A lot of HDTV sets are not going to see a 1080p/24 signal at all. They're not compatible with it. The Blu-ray player has to convert the video to a 30p or 60i format for the viewer to see a video image at all.

Most new TV sets sold in the United States are not compatible with European 50i/25p broadcast signals and playback formats. I'm wondering if any new TV sets sold in North America are compatible with PAL at all. I've looked through the specifications on my Sony Bravia XBR4 TV set and it says nothing about PAL support. It only supports NTSC/ATSC signals, PC input and 1080p/24 material via HDMI from sources like Blu-ray and my Dish Network DVR.

My TV set primarily operates at a 120Hz refresh rate. It's running at 120Hz whether I feed it a broadcast HDTV signal or a video stream from Blu-ray. That doesn't mean I have the motion enhancer turned on. Based on the signal (720p/60, 1080i/30, 1080p/24) it's flashing each video frame from 2 to 5 times. The only time the TV changes its refresh rate is when I feed it a computer monitor signal via the old fashioned analog PC monitor input jack.

Posted by Joe Redifer (Member # 3) on 05-19-2009, 11:30 PM:

And even then, it doesn't change the refresh rate, it just "accepts" it and converts it. Today's TVs need to be more versatile. I want every resolution and refresh rate supported natively, but we are not smart enough to produce such TVs. Maybe if we invent something like a cathode ray tube, but that technology is years upon years away. Any interpolation or upscaling sucks ass. However I feel that I am the only one on the planet who demands more than mediocrity.

Posted by Julio Roberto (Member # 4976) on 05-20-2009, 02:15 AM:

Guys:

Obviously one of us is fundamentally wrong. It will be hard to prove to you that, in HD such as blu-ray, you will no longer see "PAL" or "NTSC" anywhere in the product because ... blu-ray is blu-ray and all blu-ray compatible equipment must support the blu-ray aproved frame rates in the standard, which are 24, 50 and 60 (which can carry 25p and 30p signals, of course).

If you don't like the article I linked, find one that says the opposite. I'm having difficulties finding articles that "prove it" since nobody cares to talk about it anymore, as there is no difference.

Another entirely different thing is the support of over-the-air HD in the tuner. That is different and incompatible from US, Japan and old-PAL-land (most of the rest of the world). We went with different standards, each of which may or may not allow for multiple frame rates.

But even your ATSC digital over-the-air standard in the USA must support all "standard" HD frame rates:

http://en.wikipedia.org/wiki/ATSC_Standards

Look at page 9 of the standard:
http://www.atsc.org/standards/a_72_part_1.pdf

Now the USA is officially, by mandate from the FCC, 25p land (as well) after the analog switch off.

LOL.

And another thing is support for old analog NTSC and PAL. All tv's I've seen here support old-analog-NTSC and, trust me, they don't convert 30/60hz to 50/100. Lol.

And I bet most (current) HD TV's in the USA also support old (i.e. composite input) analog PAL signals. Give it a try. But not all may. Analog support is just an "added bonus", not part of the "HD" revolution.

But we are not talking about old analog content which may or may not be supported (not converted, supported). We are talking about if an HD TV, and there is no "NTSC" HD TV set or "PAL" HD TV set ... they are all "HD" TV sets when it comes to the "HD" part supports natively frame rates other than 30/60 i.e.

And yes, they all do. They all support 24/50/60 (which can carry 25 and 30 progressive).

There are no longer 100hz tv sets. They are all 120hz/240hz. In Europe as well. That only means "up to 120hz". Not "fixed to" 120hz. If they support HDMI, and there is no "PAL-HDMI" and "NTSC-HDMI", they must support all the frame rates in the HDMI standard, which are 24/25/30/50/60.

It would be stupid (and very hard to do and with very bad results) for an LCD tv, that like the article I pointed work in a sample-and-hold fashion, to try to convert any of those frame rates to any other. That is not an even multiple, that is.

Find me an article or white paper that states that an HDMI signal is converted by any modern TV from whatever the HDMI standard is sending to another un-even frame rate. Other than to try to get rid of the awfull 3:2 pulldown on some content that was necessary with NTSC. Thank God you guys got past that [Big Grin]

But you also said it yourself.

If the Pioneer Kuros "use" a 96hz fixed refresh rate ... how the hell was it showing 60i NTSC material? Did they suck big time when playing back an NTSC 60i DVD with an NTSC 60i TV series and all critics just missed the (un)even convertion to 96hz from 60i material? The Kuros could do UP to 96hz (actually, up to 100hz), and would do whatever rate was the most appropiate for them (i.e. 100hz for 25/50 material, 96hz for 24p and 60hz for 30/60 material). And that was plasma, that doesn't have such an easy time with arbitrary frame rates like LCD has.

You no longer see "PAL" and "NTSC" HD TV's other than in the over-the-air tuner they can equipped with. But get your own, separte Tuner or Satellite or Cable box with an HDMI output, plug it in you TV, and you'll see 24/25/30/50/60 frame rates supported by (just about) all w/o convertion.

It's in the HDMI standard and supported by most new TV's anywhere in the world w/o pulldown or speed ups convertion on the TV's ... that would be impossible or at least impractical.

Same with the blu-ray players. They must all support all the standard frame rates. Obviously, those for sale in the old NTSC-land would include some convertion to allow support for analog outputs (i.e. 3:2 pulldowns).

How do you think our HD TV's over here (which again, are the same as over there except for the over-the-air tuner part) react to a 24p signal? Convert it to 25p and duplicate a frame every 24?

[Eek!]

I'm having great difficulties finding a definitive, more clear article than the one I posted before because ... well, nobody talks about frame rates anymore since just about all TV's support all the standard ones and it's no longer an issue.

I can only find a few discussions in forums with some miss-informed people.

If you can find one in which someone finds objection due to sampling artifacts on a modern TV with signals at different speeds ... let me know and we'll see where they mistake was on their side. [Big Grin]

And I'm not saying that some manufacturers may have cut corners and opted for supporting only a preferred frame rate and converting all the rest from the HD TV standard to it. I'm saying I'm not aware of that being the norm at all. It's probably more expensive for them to do (in the amount of RAM needed for the temporal adjustments, i.e.) with LCD's than just hold the display and release it at a variable rate, gives worse results and, well, it would be just stupid. But I'm sure someone somewhere is doing it. I'm just saying that I don't believe that's the norm with modern HD TV's, and certainly not the case in the ones I have direct knowledge of, until someone proves me wrong.

Posted by Bobby Henderson (Member # 840) on 05-20-2009, 09:40 AM:

quote: Julio Roberto
Obviously one of us is fundamentally wrong.

Think about what you have been saying. If any HDTV set could actively change its refresh rate to adapt to any frame rate (24, 25, 30, 50, 60) then there would be no need for TV sets to include high, common denominator refresh rates like 120Hz and 240Hz.

quote: Julio Roberto
It will be hard to prove to you that, in HD such as blu-ray, you will no longer see "PAL" or "NTSC" anywhere in the product because ... blu-ray is blu-ray and all blu-ray compatible equipment must support the blu-ray aproved frame rates in the standard, which are 24, 50 and 60 (which can carry 25p and 30p signals, of course).

North American made TV sets might be able to see the 1080p/24 video on a European Blu-ray disc just fine. But the matter will be different when it comes to extras on the disc. Unless the footage is 1080p/24 it will likely be PAL-oriented SD/HD footage not compatible with North American TV sets. And then there's the matter of region coding to consider as well.

quote: Julio Roberto
Now the USA is officially, by mandate from the FCC, 25p land (as well) after the analog switch off.

Linking to a page on Wikipedia proves very little since Wikipedia itself is often polluted with errors. The fact remains the vast majority of TV sets sold in North America are not compatible with PAL style 25Hz/50Hz video streams. They're certainly not compatible with over the air DTV broadcasts in that format.

quote: Julio Roberto
And yes, they all do. They all support 24/50/60 (which can carry 25 and 30 progressive).

You're claiming every HDTV set in existence natively supports a 1080p/24 signal? I have personally seen otherwise.

Most HDTV sets in existence do not natively support 1080p/24. In fact, most sets currently in use don't even support 1080p whether it's 30fps or 24fps. They fail the 1080p/24 compatibility tests with the latest DirecTV and Dish Network HD DVRs. Some crap out and fail to display a picture entirely when the Blu-ray player or PS3 tries to force a 1080p image via HDMI or component connections. For example, our company has an older 42" LCD-TV set in our conference room. I connected my PS3 to it during an office party. The TV set only worked properly with the PS3 set to output 720p. It flickered like crazy with 1080i and didn't show a picture at all with 1080p set. A lot of people are stuck watching any high definition content converted to 720p/60Hz or 1080i/60Hz, even if it is coming from a Blu-ray player. This gets to why I waited so long to buy my first HDTV set. I knew the limitations very well and didn't want to spend a significant amount of money on a new TV set until I knew for certain many of those problems had been solved.

Posted by Julio Roberto (Member # 4976) on 05-20-2009, 01:14 PM:

No big deal, we just agree to disagree.

I think that most/all modern LCD HD TV's (and others too) support natively 50/60 (and thus 25/30) content from HDMI anywhere in the world, including content from blu-ray that origintated in PAL 50i, and you think that they either don't, at least in the USA or, if they do, they do some funky rate convertion.

I agree 24p support is spotty, but still quite ubiquos.

[beer]

Posted by John Hawkinson (Member # 1135) on 05-26-2009, 07:24 PM:

You guys have got to be more succint. Come on! Editing, please. Julio, especially; few people are going to slog through all that.

I believe that a lot of this is irrelevant because smart TVs try to reconstruct 24p video out of pulled down 23.98 or 29.97 and play it back as 24p anyhow; and they do a good job of it, so whether frames are sent 24p or not matters not much at all.

--jhawk