The Big Judder Problem and the Overhyping of 24p

Evan Powell, November 11, 2008
Contents
What Causes Judder

Your brand new 1080p home theater rig is finally installed and ready to go. You're all set to sit back and watch your favorite classic, Casablanca, like you've never seen it before, with stunning clarity and contrast. Your Blu-ray player outputs 1080p/24, the signal format everyone is raving about. You've got the Blu-ray edition of Casablanca. Your 1080p projector displays the Blu-ray signal in native 24 fps format--everything is as pure and pristine as it can get.

So, you hit the play button. The Warner Bros logo splashes onto the screen. The globe rotates slowly. The map of the Mediterranean is rendered in breathtaking sharp detail. You smile in deep satisfaction with your new system. And then it happens. At two minutes and 3 seconds into the film, the camera holds the skyline for a moment, then pans slowly down to street level. You recoil in horror as the picture comes completely unhinged. It stutters and shakes like a delirious madman. The buildings are seemingly in the throes of a bizarre earthquake. It hurts to watch it. You blink repeatedly in disbelief. How could your brand new state-of-the-art 1080p projection system with pure, native 24p transmission come so dramatically unglued?

Welcome to 24p. What you just experienced was motion judder, an extremely annoying artifact that derives from the fact that movies are filmed at 24 frames per second (fps). The 24 fps sampling rate was adopted as a de facto standard in 1926 when the budding film industry recognized they needed a sampling rate fast enough to support a coherent audio track. (The first talkie, The Jazz Singer, was released in 1927). Prior to audio-enabled movies, they were filmed at even slower speeds, in part to save film, and in part because film exposure speeds were a lot slower back then.

The industry standard 24 fps film rate is an albatross that we've been stuck with ever since. As it turns out, it is way too slow to resolve camera panning motion cleanly. So when a movie camera pans at an unfortunate speed, you get motion judder. Sometimes you get it in spades. The sad fact is, your high resolution 1080p/24 system is simply showing you the picture as encoded on the Blu-ray disc in its authentic naked form. We just never saw it in our homes quite as naked before the advent of Blu-ray and HD DVD.

Actually, we've never seen 24 fps film quite this naked even in a commercial movie theater since the double shuttering action of the movie theater's projection system reduces the experience of judder and flicker. You can see some judder in the movie theater, but it is not as pronounced as it is on a digital home theater projector playing Blu-ray or HD DVD at 24p.

But wait, wait, wait, you say...... "I thought these judder problems were related to this 3:2 pulldown thing, and once we went to 24p, we'd have a clean picture." Well, a lot of people anticipated that, because all we've seen in the NTSC world until recently is 24 fps film converted to 30 fps display. That conversion from 24 fps to 30 fps (typically referred to as 3:2 pulldown) does indeed introduce a slightly different kind of judder, as well as some blur, when the camera pans. So it is perfectly natural to assume that a native signal that hasn't been compromised by this nasty 3:2 pulldown conversion process would look better.

As it turns out, the opposite is often the case. The motion judder in native 24p can be atrocious. You can test it yourself if you have the equipment to do it. We'll assume that if you have a Blu-ray player, you are more likely to have a copy of Casino Royale than Casablanca. If you do, find a messy panning scene in Casino Royale. There are lots of them, but there's a real beauty in the 9th chapter, starting at 1 hour, 11 minutes and 13 seconds. The dealer is dealing, and the camera pans slowly around the table.

In 24p playback, this scene is a pure, unmitigated disaster. The people seated at the table come apart at the seams, the tuxes flash and strobe, the Casino Royale logo on the card table blinks like a neon sign. Once you've replayed this travesty a few times, switch your Blu-ray player to 60p output and run it again. Yes, it is still a mess. But look at it closely ... the juddering effect is actually reduced. That is because the 3:2 pulldown is blurring and masking some of the latent motion judder in the film. There is certainly a separate conversion judder that is added to the visual stew with 3:2 pulldown, but oddly enough it works in contravention of the latent 24p judder. The net effect is that the image is a bit blurred, and the overall judder is noticeably reduced. Scenes like this do not look great in 60p, but they look worse in 24p. After all the hype over 24p (the benefits of which we eagerly anticipated as much as anyone), it must be admitted that 60p playback can, in the final analysis, be less distracting for many people.

Contents: What Causes Judder Minimizing Judder Judder Elimination

Reader Comments(12 comments)

Posted Apr 29, 2014 8:43:41 AM

By Pete

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Films even judder at the movie theaters, even the ones boasting about 4K digital. Everything looks like total [censored] these days, but the majority of people can't tell.

Posted Apr 2, 2014 4:07:11 AM

By Kelvin

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This article is now out of date. TVs like Samsung have "Cinema Smooth" for 24Hz mode which doubles or quadruples the frame rate *without* interpolation (so you don't get the soap opera effect). It looks exactly like what you see in the cinema and it's a lot better than 60Hz.

Posted Mar 14, 2014 7:59:58 AM

By linto

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very informative article...

Posted Jun 12, 2013 2:10:02 PM

By SOTIRIOS

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Dear all, I am not an expert, yet I need an advice. I bought a Harman Kardon BDT 30 blue ray. When I watch a film periodically seems that the film speed slows down and after few seconds catches up. My tv is 120hz. What do I have to do in order to watch my discs without any visual problem. Change my tv. And if yes what do I need to know in order to buy one for maximizing my blue ray performance. Thank you in advance.

Posted Dec 31, 2012 6:40:32 PM

By RNMills

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just in reply to 'your reader' regarding the Sony Tv and judder.

I have had a Sony 40" lcd Tv for a while, and it has a function called 'film mode', which is different to the nasty motionflow (turn all that off), and seems to be there to eliminate judder from 24p and/or 3:2 pulldown. Set to Auto1, it worked brilliantly.

I recently upgraded to a newer Sony 40" led 3D Tv, which also hzs the same feature. Unfortunately, there is something wrong with it in the newer set. With it turned on, it still smooths out the judder, but for some reason causes the picture to also frequently 'pause' on frames. It's infuriating, and i had to turn it off in the end, and just put up with tne inherent judder. So i am not happy here, the tv is in this sense a step backwards, and also interlaces really badly on standard def footage, another problem that the previous model didn't have. Sony do periodically system updates for the set, and i'm hoping that there may be fixes for both problems in time.

Basically it's best to just experiment with your tv. try auto1 on filmmode, with motionflow turned off (especially if it's 3d, where motionflow vastly increases judder), and if that doesn't work, just tyrn filmmode off (not Auto2), and make the best of it... :/

Posted Nov 15, 2012 6:10:59 PM

By Darryl G. Jones

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As to the three blade shutter comment: I have worked as a theatre projectionist since 1968. Rarely do theatre film projectors use three blade shutters. The reason is that they reduce the light output too much. The typical theatre uses 2 blade shutters. Three blade shutters are used in industry screening rooms; the main reason for this is to reduce the flicker to almost nothing. I was never bothered by "judder" until IMAX came along. The large 70mm frame greatly enhanced clarity due to less magnification and less apparent grain. The clarity of IMAX unfortunately made the judder much more apparent than what it had been before. Showscan developed by Doug Trumbull captured images at 60fps and projected them at that rate. The system used 65mm negative stock which was contact printed to 5-perforation 70mm. The result was the screen was more of a "window' than a screen and the result was breath taking. The system was never adapted for feature release due to cost but the end result made 3D simply look silly by comparison. Digital capture and projection will eventually offer higher frame rates in the future.

Posted Oct 20, 2012 8:40:12 PM

By Filmsnob

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{Inappropriate remark delete} 1. Films are actually projected ON FILM with a 3 bladed shutter--not a 2 bladed shutter--giving 3x1/144 of picture and 3x1/144 of black for each frame. You just can't duplicate that on video because video technology does not incorporate those periods of black. If you watch films on FILM you won't ever see ANY "judder."

2. Film exposures are 1/48 fps for normal playback. The typical shutter on a motion picture camera is 180degrees (half of a pie). But that is not universal and many professional motion picture cameras have variable shutters, so the exposures can be longer or shorter than 1/48.

3. At 1/48 exposures, you get some motion blur in a tracking shot; that's what prevents "judder" when watching projected film on FILM. I don't have Casino Royale in front of me so I won't comment, but for comparison, look at the film, then the 23.976 video then the other flavors of video to understand the translation problems and their successes and failures. Taking any electronic representation of a film frame and then making inferences about the original is hopeless.

4. People who know nothing about film technology should should refrain from spreading misinformation based on inference from another technology, i.e. video. It's like apples and oranges.

Posted Oct 8, 2012 4:39:00 PM

By stephen

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Frame interpolation looks like crap. I will say it now, there is something magical about 24 frames even with it's limitations. If you've ever seen film at a higher rate (say 48fps) it looks like garbage. You argue that it is only because of our own paradigm but I disagree. I can't believe you would recommend frame interpolation to anyone who likes movies.

Posted Jun 9, 2012 8:51:04 AM

By Cassiel

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I have a blu ray player capable of 24p output and a plasma monitor able to display 24p (or better 23,976p) Once the 24p signal arrive the internal scaler is set to 96p, meaning each 1/24th of a second one frame is repeated 4 times. Blade Runner, Casablanca, you name it looks INCREDIBLE FILM LIKE. Just WATCH the begining credits of Blade Runner how smoth the glide on screen as other but particularly those ones.

Posted May 19, 2012 11:36:19 AM

By Brian berneker

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The judder you describe can also probably be eliminated by setting your television to 120Hz and thereby bypassing telecine frame duplication by using 5:5 pulldown and having a consistent stedy frame rate.

Posted May 14, 2012 6:43:41 AM

By Amazing

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[edited]

Pro tip: If you think you've figured out something that is contrary to what all of the experts/informed people think and you've never seen anyone draw the same conclusion as you: you're wrong. Or at least 99.999999999999999% likely to be wrong.

"Judder", as it is poorly being described here, is not judder at all. Judder is ACTUALLY a disconcerting difference in display time on alternating frames, as is seen in 3:2 pulldown. One frame will stay on the screen for 50 ms, the next for 33 ms, the next for 50 ms, and so on. Some people notice it, others have no issues.

What is being described here is, again, NOT judder in any form or fashion. The author is taking 3 pages to describe the visual effects of a mismatch between the low frame rate of film and the exposure time of each individual frame (which I certainly have no issues with, outside of the misleading and incorrect usage of a well established term).

If the film exposure were actually 1/24 second, then the screen would be a blurry mess any time something moved. The actual exposure time is typically 1/48 or faster. This introduces a gap in visual information that the brain finds disturbing. It is present in any perfectly displayed/projected 24 fps film due to (as the article appropriately points out) film industry idiots failing to update their standards to even 1950's/60's technology. At this point, all films should be 4k/60 fps. NO excuse except for film industry "stuck in their ways" stupidity and some "critics" find >24 fps to be "soap opera-ish" and disturbing. I think those people should be forced to stare at 24 hz of alternating black and white frames for eternity.

Hopefully Peter Jackson kicks the industry in the teeth with his 48 fps Hobbit films and we start getting more films coming down the pipe that aren't a flickery vomit inducing mess.

Posted Feb 2, 2012 7:04:49 AM

By your reader

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hi Evan,

i bought a sony ex520 32" led tv. it has 24p and a refresh rate of 60hz. i have read that this model has blu-ray judders. i don't have a bluray player yet, but i was planning to buy one. will i be greatly disappointed? will my movies shake, tremble and stutter?

and is there a solution to this problem? please reply.

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