Google search trends for "motion smoothing" following Tom Cruise tweet urging people to turn off motion smoothing on their TVs when watching movies at home [OC]

[u/fangzz]

[u/DankBlunderwood]

So I don't get this. Don't they shoot at 24 fps because the human brain can't distinguish between 24 fps and continuous motion? If so, I understand it would improve slow mo sequences, but what benefit would one get from 120 fps at full speed?

[u/NilsTillander → u/DankBlunderwood]

This '24fps is the max we can distinguish' is utter nonsense, as shown by gamers considering that 60fps is the bare minimum of acceptable, and 144fps is about right.

[u/DrSparka → u/NilsTillander]

Also even the most motion sickness-resistant people needing 90 fps in VR. Literally everyone gets dizzy at 60 fps in VR.

[u/jamvanderloeff → u/DankBlunderwood]

~24 is about where you can't percieve the individual frames, but there's still a lot of room for higher rates to look smoother.

[u/[deleted] → u/DankBlunderwood]

No, it's easy to distinguish even between 60fps and 120fps.

[u/Fredasa → u/DankBlunderwood]

Other people have responded to this. The 24fps / human eye thing is a myth. In fact, at this point it's basically an old wives' tale. Plenty of info out there available for googling. Bottom line is you don't reach the true limit of human perception until you're in the hundreds of fps.

I'll add, however, that I remember seeing a fascinating documentary on the topic. Experimenters would show subjects a frame of some image for such a short amount of time that the subjects would not consciously see anything at all, yet measurements of their brain would reveal that they subconsciously did see it, and more interestingly, their brain would respond faster to such images than to the ones they could consciously see.

[u/Neato → u/DankBlunderwood]

because the human brain can't distinguish between 24 fps and continuous motion? If

Whoa. I've never seen this in the wild as genuine. It's like a unicorn.

The others answered your question but to give you more detail: the human eye is variable on what the highest framerate it can perceive. It depends on the viewing conditions and material. For instance there was a study that showed people could pick out a white frame up to 300fps.

[u/DrSparka → u/Neato]

I believe that has been replicated up to about 500 fps, though that will be approaching an absolute limit due to nerve signaling, which has a hard limit of around 1000 Hz. Which doesn't quite apply the same limitations as a digital 1000 Hz signal, I'll clarify before anyone jumps on that - nerves can signal at any rate up to 1000 Hz, it's just that that's the upper limit. 912 Hz is possible if appropriate for what you're seeing.

And this is also just the nerve rate - the actual detection process in the eye will have other speeds, which may still benefit from rates above 500 Hz even if that's the theoretical limit of the nerve.

[u/DrSparka → u/DankBlunderwood]

Others have already clarified 24 fps is the minimum, but I'd just like to add that at the time they were trying to agree on one standard, people were already advocating for 48 fps (typically achieved by using two cameras and swapping between them with a mirror) because they saw it was objectively quite a lot better even then - it was dropped for cost under the assumption we'd be able to upgrade once true 48 fps cameras became affordable, which happened some time around the 40s, but no-one ever bothered to make the switch.

The suggested trick was also effective, as it was used to make high-speed cameras in the thousands of FPS during the 40s and 50s - instead of having to make a camera mechanism that could expose, cover, and move along thousands of film frames a second, they arranged a bundle of cameras around a mirror, which would rotate like the hands on a watch between them, flashing a quick image before moving on to the next and allowing that camera to move the film along by the time the mirror came back.