Why stuttering in 24p content is something we'll have to live with for a long time

[matbezlima]

First, I need to establish some things.

The lack of a consistent meaning to the terms "stutter" and "judder" across all industries is very frustating. As a ground rule, I think it is better to define "judder" as uneven frame pacing (such as a 3:2 pulldown to fit 24fps in a 60Hz refresh rate, which means that some frames will stay on screen for longer than others), and "stutter" as the issue I will actually be talking about here in sample-and-hold displays.

The definitions I am using for stutter and judder here are how RTINGS, a site of specialists in reviewing TVs, defines them. But be aware that in many contexts, it's common to see the term "judder" being used with the meaning I set here for "stutter", and vice-versa.

Now I ask you guys to please watch the video below before proceeding to read the rest of my post. It explains in great detail what is "eye-persistence motion blur" (and keep in mind that whenever I say just "blur", I mean "eye-persistence motion blur"). It explains the concept far better than I ever could, with very educative and helpful graphs, so please watch it before reading the rest of my post. The video is overall great aside from three small technical hiccups. There is one instance when he says "microsseconds" when it should be miliseconds. There is a moment when he says "smooth", thought he meant "less blurry", at 14:27. And, at 15:30, what he calls "24fps judder" is actually 24fps sample-and-hold stutter, as we have defined the terms previously.

YouTube

Now, to understand the stuttering issue, we need to keep in mind what is a sample-and-hold display, and also that all our modern monitors/TVs, such as LCD, OLED and QLED, are sample-and-hold. Such displays hold the entire frame, from top to bottom, completely static in your screen till it transitions to the next frame. The faster the TV's gray-to-gray pixel response time is, the longer the whole frame stays completely static on the screen. Gray-to-gray is how long it takes for the pixels to transition from one color to the next.

For such displays, there is a stutter-to-blur continuum, and the frame rates at which stutter transitions to blur gets higher the better the display's grey-to-grey response becomes. The stutter of any object we track on the display follows the same law of eye-persistence motion blur, as the basic principle is the same. Don't forget the stutter-to-blur continuum. With slower grey-to-grey response, it adds more blur, and it makes the frames blend more into each other, lessening stutter. Gaming monitors and high-end TVs all have very, very fast grey-to-grey response time. Hell, even the mid-tier TVs nowadays have good response times, which maximizes stutter.

If you want to really did deeper on the technical side of this, check out this Blur Busters article, about the journey to 1000Hz sample-and-hold displays.

https://blurbusters.com/blur-busters...mple-and-hold/

Such displays will be the Holy Graal of display technology. They will be able to display any frame rate perfectly. You would be able to simulate the look of a three-bladed shutter film projector. Actually, you can do this in a 144Hz display (though HDR and overall image brightness will take a HUGE hit). How? Spread the 24 frames every second across a refresh rate of 144hertz. But instead of displaying each frame for 6 refresh cycles, do it like this:

Frame 1, black frame, frame 1, black frame, frame 1, black frame.

The same will be done to frames 2, 3 4, and so on. You will see that it will fit neatly with a 120Hz refresh cycle of a sample-and-hold monitor! By doing this, you will also get the motion artefacts of such projection: as the flickering refresh rate (96Hz) is three times higher than the frame rate (24fps), you will get triple images. Remember the double image artefacts in CRTs when displaying 30FPS?

In a 1000Hz display, you could simulate a panel with an extremely slow grey-to-grey response time whenever displaying low frame rate content. By doing this, the extra blur added will make the frames blend into each other far better, dramatically reducing stutter.

Of course, you will always want fast gray-to-gray response times for high frame rate content, such as videogames. You will want as little blur as possible. And remember that the stutter of low frame rates becomes blur in high frame rates. But even if you had a sample-and-hold display with instant gray-to-gray response time, you will still see far more blur in 60FPS being displayed in it than you will in a CRT. The phospor doesn't glow for long, so CRTs have very low persistence. But you will have understood all of this already if you saw the video and read the article.

Last, but not least, I wonder if 120Hz refresh rates of modern TVs aren't already enough to simulate a slow gray-to-gray response time panel. I wonder if we really need 1000Hz for that. If 120Hz can simulate a very slow gray-to-gray response time panel, then why haven't TVs done that already rather than traditional motion interpolation, which introduces the dreaded soap opera effect?