24fps vs. 60fps - AVS Forum
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post #1 of 11 Old 07-08-2009, 09:11 AM - Thread Starter
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Let me first state that my TV's resolution is 1366x768. I notice on my Blu-ray player, there is an option to have movies play at 24fps. It's set to 60fps, by default. I've read everywhere on several sites that if your TV is capable of accepting 24fps, I should use that feature as it will give better results. Well, on my TV, it seems to be the opposite. If I set it to 24fps, my TV accepts it, but I notice that there's a little more noticeable motion blur present, not to mention that the input lag is slightly longer. On 60fps, there is less motion blur and the input lag isn't as bad.

Why exactly am I not getting the best results from 24fps? Is it because 24fps only works well with 1080p TVs?
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post #2 of 11 Old 07-08-2009, 09:34 AM
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Quote:
Originally Posted by xraffle View Post

Why exactly am I not getting the best results from 24fps? Is it because 24fps only works well with 1080p TVs?

Many (most) films on BD are stored in 24fps and many BD players can output this in native mode. Doing so does not require any reverse telecine. The idea is to output 24fps and have the video display device display the picture at a multiple of 24, i.e., 48, 72, 96, or 120. See if you can select the scan rate on your monitor or see if will tell you the scan rate. If selectable start with 72. If it will only do 48 then you may be seeing some flicker from the picture.


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post #3 of 11 Old 07-08-2009, 09:39 AM
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Yes.

24 frames only works with 1080P. Your tv can't do that so it can't do 24 frames.
Accepting the input is not doing it, as it just converts back to 60 hz and you lose quality.
You also lose having to down convert the scan.
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post #4 of 11 Old 07-08-2009, 10:05 AM - Thread Starter
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Quote:
Originally Posted by jhe View Post

Yes.

24 frames only works with 1080P. Your tv can't do that so it can't do 24 frames.
Accepting the input is not doing it, as it just converts back to 60 hz and you lose quality.
You also lose having to down convert the scan.

Thanks. That makes sense.
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post #5 of 11 Old 08-20-2009, 07:46 AM - Thread Starter
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Ok, I've been doing some serious research on this and I read that the motion blur I'm experiencing is normal. 24fps is suposed to have motion blur in order to give the motion a more fluid and realistic effect. An example they give is to wave your hand in front of your face. When you wave your hand, you see the motion blur. I'm still puzzled as to how motion blur is supposed to make the picture better. I'm confused.

For those of you that have the expertise on this, what exactly is the difference picture-wise between watching Blu-ray in 24fps and 60fps?
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post #6 of 11 Old 08-20-2009, 07:39 PM
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Motion blur is what's created by the slow shutter speed of the original camera during filming. If you don't have that, you get a "stop motion" effect; you can tell that you're watching a sequence of still images.

There are lots of other artifacts that you _don't_ want, though. I don't know specifically which ones you're seeing.

The big difference between 24fps and 60fps _progressive scan_ is an artifact called "judder". This is the slightly uneven motion caused by the fact that 60 is not divisible by 24. If you have two frames which follow each other called A and B, then you should see A displayed for 1/24 of a second, and B displayed for 1/24 of a second. On a 60Hz LCD or plasma TV, you will instead see frame A displayed for 1/30 of a second, and frame B displayed for 1/20 second. So uniform motion won't appear uniform because the frames aren't displayed for the same length of time.

BTW, it's not completely true that you need 1080P to display 24fps. But it's mostly true; there are few exceptions.
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post #7 of 11 Old 08-20-2009, 08:03 PM - Thread Starter
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So you need a 120Hz TV in order to benefit from 24fps?
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post #8 of 11 Old 08-21-2009, 09:00 AM
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In order to eliminate judder from 24fps content you need a display that can display each of the frames from the 24fps content the same number of times. A 120Hz display can do this since 5x24 =120 and it can display each frame 5 times. A 60fps second display displays 1/2 of the the frames 3 times and the other 1/2 2 times.
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post #9 of 11 Old 08-22-2009, 09:30 AM
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Quote:
Originally Posted by xraffle View Post

So you need a 120Hz TV in order to benefit from 24fps?

Yes.
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post #10 of 11 Old 08-22-2009, 10:57 AM
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Quote:
Originally Posted by xraffle View Post

So you need a 120Hz TV in order to benefit from 24fps?

Or 72 or 96--even multiples of repeating a 24p frame. 120 Hz may mean a frame-interpolation system (some LCD displays, for example), manufacturing additional frames rather than just repeating a frame. -- John
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post #11 of 11 Old 08-22-2009, 11:04 AM
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The better quality 120Hz LCD TVs do frame intrpolation when receiving 60fps content and do 5:5 pulldown to elimnate Judder when receiving 24fps content. AFAIK there are even some top quality 120hZ Models when sensing that they are receiving film based 60fps content as opposed to video based will perform Inverse Telecine processsing to recover the 24fps so that they can use 5:5 pulldown.
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