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This topic comprises 2 pages: 1 2
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Topic: Are 120hz televisions ideal for 24fps blu ray playback?
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Cameron Glendinning
Jedi Master Film Handler
Posts: 845
From: West Ryde, Sydney, NSW Australia
Registered: Dec 2005
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posted 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.
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Julio Roberto
Jedi Master Film Handler
Posts: 938
From: Madrid, Madrid, Spain
Registered: Oct 2008
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posted 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.
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Bobby Henderson
"Ask me about Trajan."
Posts: 10973
From: Lawton, OK, USA
Registered: Apr 2001
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posted 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.
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Julio Roberto
Jedi Master Film Handler
Posts: 938
From: Madrid, Madrid, Spain
Registered: Oct 2008
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posted 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.
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Bobby Henderson
"Ask me about Trajan."
Posts: 10973
From: Lawton, OK, USA
Registered: Apr 2001
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posted 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.
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