120hertz TV's and 24p

[sdeming]

My buddy just picked up a 40 something inch tv with a 120 hertz refresh rate. To celebrate, he watched Black Hawk Down. Later when we were talking about it, he told me that the tv took some "getting used to". He said that Black Hawk Down looked like a BBC documentary, and not like a movie. He went on to say that tv shows like LOST, looked...weird. Good, but strange somehow.

I started thinking about what he said about Black Hawk Down looking like a BBC documentary. If BHD was filmed at 24fps with a 180 degree shutter, we'd be used to watching this on a tv with a 60hertz refresh rate. Now, if we started watching those same movies (and TV shows that are filmed at 24fps like LOST) on a tv that doubles the refresh rate...would the fps be doubled too? Or at least, would you perceive double the frame rate? This would be why he thought BLD looked like a BBC documentary, if the frame rate were doubled to about 48fps this would be quite close to 50fps which is a PAL standard.

Obviously, watching sports or playing video games with a fast refresh rate is preferred. But film, which intentionally bathes itself in motion blur - looks, well, weird.

[CycleWriter]

I watched Iron Man on a 120hz HDTV. It looked very strange, to the point of distraction. It was somewhat unnatural, to my eyes. Convinced me that I didn't want one. I can live with the lower quality of sports broadcasts on my 60hz unit, but I want my BD movies to look as they did in the theater.

[iThinkergoiMac]

It looks so incredibly smooth because 24 divides evenly into 120, but not into 60. So, when watching a 24p movie on a 60 Hz TV, each frame is refreshed 2.5x. Every other frame changes halfway through a refresh on the TV, giving it the slightly stuttering effect. 30 fps video doesn't suffer this problem. On a 120 Hz TV, the screen refreshes 5x per frame, with every frame change coinciding with a screen refresh. This makes the video appear much smoother. 30 and 60 fps also go into 120 Hz evenly, so they will appear equally as smooth. It's distracting because our eyes are used to seeing 24p displayed on a screen that can't truly display it. Whether this is good or bad is, in the end, up to the user.

To answer your question, no, 120 Hz TV doesn't magically up the frame rate. It just refreshes more times per frame. What it really is is a lowest common denominator deal in reverse. 120 Hz (fps) is the lowest number that 24, 30, and 60 will all go into evenly. It's actually capable of displaying all those frame rates properly, while normal TVs technically aren't.

It looks like a documentary because those are typically shot in 60i, which plays back smoothly on a 60 Hz machine. Our brains have associated "smooth" with documentary/behind-the-scenes/soap opera/etc and "jittery/stuttery" with movies/high quality TV shows/etc. Technically, on a 120 Hz TV you're seeing 24p as it was meant to be seen, but if you're used to seeing it differently, major distraction!

Personally, I like how smooth it is and would love to pick one up someday... I know plenty of people who hate it, though.

@CW: Interesting comment about seeing them as you saw them in the theater. I know the couple times I have gone to see a movie in a theater with a really top-notch projection system, it had the same "unnatural" smoothness to it. I wonder if digital projectors are still 60 Hz with 24p movies, giving the same illusion of stutteryness. The main catch would be projectors that are still using film... they don't have that "unnatural" smoothness but should still be truly 24 fps (and technically 24 Hz as well) unless there's another shutter going at 30 fps.

[Koppel]

Turn off all the image quality aids, 600Hz sub-field motion, dynamic contrast and such and then see the movie again.

120Hz doesn't make anything smoother. Playing a computer game on a 120Hz CRT that had a framerate of 24fps still had a crappy framerate and was unplayable.
120Hz means that a frame from a 24p footage gets shown exactly 5 times.
In a movie theater one frame is shown 2 times, basically at 48Hz.

The most annoying thing for me when watching video on a computer monitor is screen tearing: http://en.wikipedia.org/wiki/Screen_tearing
Because the framerates of the video and the display does not match.

There is a feature in computer games called "Vertical sync" that helps. The graphics processor keeps the game at exactly 60fps, and since the display is also 60Hz there is no inbetween frames being shown.

120Hz does the same for video, framerates match.
Although TV-s are better at hiding this tearing phenomenon by using some complex algorithms, blending frames together and such.

So there shouldn't be much difference between a 100Hz LCD and a 120Hz one. Living in a 50Hz PAL land, I don't think the 120Hz is going to be very useful here.

[iThinkergoiMac]

There is a feature in computer games called "Vertical sync" that helps. The graphics processor keeps the game at exactly 60fps, and since the display is also 60Hz there is no inbetween frames being shown.

I agree with everything you said except this. The computer will keep the game at 60 fps, but only if it's capable of doing so. The simple explanation is that the computer redraws the screen in sync with each refresh, approximating the frame rate at which the computer can play back the game. For example, my computer can play Halo pretty well, but it can't do 60 fps unless I turn everything all the way down. V-sync still gets rid of the tearing, though.

[Khaver]

One of the features of these higher refresh rate TV's is motion interpolation. They actually "try" to fill in movement between frames. That's why movies look "different" on these TV's. When a theater shows a 24fps movie at 48fps, they aren't adding anything between frames, only showing a frame twice, you still only see 24 different pictures per second. As time goes on we will start getting used to the BBC documentary look as more movies are released digitally for IMAX and 3D.

[sdeming]

One of the features of these higher refresh rate TV's is motion interpolation. They actually "try" to fill in movement between frames.

That explains the 'BBC' look.

[iThinkergoiMac]

So, in theory, one could turn off the motion interpolation to get a more accurate view of the video and still benefit from the 120 Hz refresh rate.

[Khaver]

I don't have one of those TV's but it would make sense that you should be able to turn off that feature. Don't know for sure though.