Home Featured It’s Not You, It’s Your Television’s Framerate

It’s Not You, It’s Your Television’s Framerate

by alexis
Man who's angry about frame rates

I got a question from a friend of mine, and I thought it might be worth sharing my answer with a wider audience. He asks:

“What’s the short answer for why new 120hz screens make films look like video? I don’t know if you have had a chance to observe this yet, but it will effect you because it makes everything look like the ‘behind the scenes’ footage on a dvd, or raw dailies. People seem to love it.”

Well, I can attest to the fact that not everyone loves it, in fact the cinemaphile/home theater boards are filled with invective regarding how this feature despoils the cinematic experience, and I completely agree with them. I’m all about respecting the filmmaker’s intent regarding how they wanted the film to look, so whatever framerate they created their program using, that’s the framerate I want to watch it at.

The reason for the difference in “look” between 24p video viewed natively and 24p video that’s been converted via 120hz digital magic is virtually identical to the difference between 24p film and 29.97 video frame rates. We’ve all grown up with juddery 24p frame rates looking “cinematic,” even though the motion sampling is, strictly speaking, pretty crude compared to what is now possible.

On the other hand, since the motion sampling of interlaced 29.97 video is effectively 60 fps, “video” motion has traditionally looked much smoother, more “real life,” or more like a TV newscast.

The newer 120hz displays use motion estimation to generate/interpolate new frames in-between the original frames of the 23.98 image stream on a DVD/Blu-ray, and so the “cinematic” motion of 24p is changed into the “non-cinematic” look we generally associate with video, all because of the introduction of a smoothness of motion where there was none before. The result, to my eye, is that classic motion pictures end up looking like a shot-on-video sitcom.

Incidentally, speaking for myself I find that the reverse can also be distracting. I’m increasingly seeing 24p-acquired video used in programs like the PBS newshour, the result being a somewhat “cinema” look within traditionally interlaced video programming, which I confess looks a bit odd. I’m just not used to it, and I believe this effect is solely based in what we’re used to.

It’s entirely possible that, someday, the next generation may get so used to 60p that 24p will be looked upon as quaintly as silent film or black & white, (at least, if James Cameron has his way). However, there are so many advantages to the low-bandwidth of 24p that I suspect, similar to interlacing, 24p motion sampling will be around for a long, long time. (And I’m not even going to get into the debate over the “intrinsic” cinematic value of shooting one’s projects 24p and 24p only, this particular article is about watching movies, not making them.)

My friend went on to reply:

I can see that showing the same thing 5 times would look different than showing me the thing, and a thing, then a half a thing mixed with half of the next thing. [My note: this is a fantastic description of 3:2 pulldown insertion] I just wasn’t expecting it to change the character of the images so much. Seems like the old way is closer to what it looks like in the theater. I wish my dvd-blu-ray player could just do 24 frames without the pulldown. You kids, give me back my vinyl 78s!

I suspect most of you already know what my reply is, but for those who don’t, I’ll enlighten you.

If you’ve got a good flat-panel display (television or projector), and especially if you’re using HDMI (and really, who isn’t anymore), you should be able to set up your player/display combo to play back actual 23.98 right now.

You usually have to enable the settings manually within your gear’s menus, but the DVD specification (and now Blu-ray) has always allowed distributors to author a DVD with an encoded 23.98 video stream—all players are supposed to do 3:2 pulldown insertion when necessary in order to display content on a non-24p-capable TV. If the TV can handle 23.98, then the player can send it directly via Component or HDMI.

So there you go. If you get a new TV and your movies look like television news, do yourself a favor and disable that pesky 120hz interpolation mode. You’ll be surprised at the difference.

Added 1/12/11—There’s an interesting thread in the comments. Nothing is ever simple! Also, it was pointed out to me that Tom Lehrer, the mathematician, songwriter, and satirist, did not in fact host the News Hour. That would be Jim Lehrer. Of course, now it’s just the News Hour, so I’ve eliminated the names altogether.

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Patrick Moynihan January 11, 2011 - 11:16 pm

120Hz isn’t the problem. The motion interpolation is the problem. The motion interpolation feature can be turned off independently from the 120Hz feature in most cases. Here’s why you want it on:

A typical TV 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. If it does, you need to turn off the motion interpolation feature.

Patrick Moynihan January 12, 2011 - 12:49 am

Clarification: The first paragraph above should read:

120Hz isn’t the problem. The motion interpolation is the problem. The motion interpolation feature can be turned off independently from the 120Hz feature in most cases. Here’s why you want 120Hz:

Alexis January 12, 2011 - 1:23 am

Hi Patrick,

I understand what you’re saying, but I’m not entirely sure I agree, at least not based on the televisions I’ve set up so far. I personally watch a Panasonic TH-58PZ800U at home, which has an “Advanced Picture Setting” in the menu of 24p 60Hz, which according to their documentation “Achieves more cinematic playback by reproducing the movie contents at twice the speed of 24 frames per second (60Hz/48Hz).” Confusingly written, but I get their point.

I have been under the impression that 120Hz was usually tied to at least a certain amount of motion estimation for “smoother” playback, but I’m happy to be wrong. A writeup on the subject at CNET (http://reviews.cnet.com/4520-6449_7-6792632-1.html) seems to imply that 120Hz and motion smoothing are tied together in their tests, but they’re not specific about whether these two capabilities can be uncoupled. I’d love to find out more regarding what models and what menu options would allow this uncoupling.

On the other hand, I disagree with the notion that the motion artifact known as “judder” is due to 3:2 pulldown. Judder, the “stuttering” that can be seen in a shot where a film camera pans quickly across a scene, is a function of 24 fps acquisition, and judder can be seen in projected movies of any vintage, in movie theaters (despite film projectors shutters being run at 48Hz or 72Hz in order to avoid “flicker,” which is different from “judder”).

In fact, it’s my experience that 3:2 pulldown will actually ameliorate judder by virtue of the field blending that is part of the 3:2 pulldown cadence.

Both fortunately and unfortunately, running a TV at a straight 24p (48Hz) reintroduces the judder, pure and unmoderated, that audiences enjoyed during the original theatrical release. However, that’s the 24p experience. Like it or not, if you’re not seeing judder, you’re not seeing what folks in the movie theater were seeing. How important that is is up to the viewer, but as I said, I’m a purist and I like the closest experience to the original presentation that I can reasonably obtain.

Chris January 12, 2011 - 12:33 pm

The News Hour with Tom Lehrer? I would totally watch that show.

Alexis January 12, 2011 - 12:43 pm

Ah, I’ve given away my UC Santa Cruz alma mater! I of course meant “Jim Lehrer,” but I agree, an hour of news from Tom Lehrer would be unimaginably fantastic. I’ll make a correction…

….no wait ADJUST YOUR TELEVISION « January 12, 2011 - 2:30 pm

[…] of flat screen HDTV’s in general. Today I came across an article by Alexis Van Hurkman ( http://vanhurkman.com/wordpress/?p=786 ) that explained a feature called True Motion that is included in a lot of the newer […]

Zak Ray January 20, 2011 - 7:34 pm

“It’s entirely possible that, someday, the next generation may get so used to 60p that 24p will be looked upon as quaintly as silent film or black & white, (at least, if James Cameron has his way).”

I think it’s important to note that Cameron was testing 48p as well as 60p… given the choice, I’d be willing to be he supports 48.

Alexis January 20, 2011 - 10:57 pm

Good point. I’d be curious to see the difference between footage shot at 48fps and 60fps, progressive frame.

rodrigo monje April 14, 2011 - 6:01 pm

I totally agree with Alexis: 120hz, motion smooth, motion interpolation and so on are NOT the way I like to watch films, I like the cinematic look with that special atmosphere it can offer. I Hate the video look that create 120hz in feature films.


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