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Comment by TacticalCoder | Hacker News Reader

When I was a kid I was taught by every adult that "humans cannot discern more than 24 fps".

Except that we could all immediately tell if a Commodore Amiga demo was running at 25fps or 50fps and groups that'd have the frame rate drop from 50 to 25fps on some frames were "lame".

So I knew it was obviously false that humans couldn't discern when something was running at more than 24 fps.

Same when little Windows 95 utilities allowed to bump the framerate from 60 to 72 or 75 Hz. I remember those: they'd enhance the experience. Yet everybody was still telling me: "Why do you even bother, 60 Hz is enough, humans cannot discern more than 24 images per second".

Same for cats and dogs and the TV of course. Which I knew was wrong because on my Commodore Amiga I'd take a big circle, filled with a solid color, and make it bounce across the screen and watch my cats' reactions.

People can be really extremely dumb, even in the face of evidence.

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The claim that nobody could discern more than 24 fps is an odd one (and not one I've ever heard), since it's been generally known that's not true even back before 24 fps was chosen as a standard. Originally some (including Edison) wanted to standardise on higher frame rates for better motion. 24fps was basically compromise to balance against the amount of film used, being fairly close to the minimum speed that was considered satisfactory for motion.

Even then, a two bladed shutter was used to flash the image on the screen twice for each frame, and more modern projectors used a three-bladed shutter to reduce flicker.

> being fairly close to the minimum speed that was considered satisfactory for motion.

Basically that: It's a repeated and extremely common misunderstanding of the actual claim, that 24fps is right about the threshold between interpreting a series of images as motion instead of a series of images.

A lot of people assume that once you see it as motion, there's nothing more that can be gained.

Fake knowledge was the most common thing circulating among people back then.

People mostly couldn't verify anything.

> People mostly couldn't verify anything.

May I inquire: How do we verify things today that we did not back then?

The literature is all there on the internet. If you want to repeat the experiments, the instructions are all there on the internet. If you want to look at the theory from what the fact was derived, it's there on the internet.

Approximately nobody had access to anything before it.

This is basically just a misunderstanding. There are multiple overlapping effects. Most of the 'hard' numbers for claims along those lines come from the flicker fusion frequency [0] around 50 Hz or so, which means that a video recorded at 25 fps and replayed by flashing every frame twice (like in old movie theaters) will not appear to flicker.

However, there's another important factor, which is that if you move an edge accross your visual field and sample at a certain frequency, depending on the speed of the edge, you might get a stroboscope-like effect and see multiple parallel edges. This is something a lot of people notice in 60 Hz computer rendered video, or when moving quickly under a lamp flickering at the mains frequency, because every frame is sharp without any motion blur. By contrast, you can run video filmed at an exposure time similar to the frame time at lower frame rates and it'll look fine, because the motion blur removes that stroboscope-like appearance.

[0] https://en.wikipedia.org/wiki/Flicker_fusion_threshold

There is research on humans showing that we can perceive at 500 Hz. There are devices that try to simulate a color by modulating a single LED (no color filter) and they don’t work on humans until you go past around 1 kHz.

https://www.nature.com/articles/srep07861

Yes, that's what I was referring to. If you have an edge flickering at a high frequency and perform a saccade (fast eye movement) over the edge, your retina will be exposed to the edge at regularly spaced intervals. So the motion will not appear smooth. That's what they call a 'flicker artifact' and I called a 'stroboscope-like effect'.

Importantly though, this is not us humans detecting 500 Hz flicker itself, quite the opposite -- the reason the artifact is visible is that our retina is not sensitive to fast motion, it integrates over a period of time in which the edge appears to be in multiple locations.

Indeed, I think that you can definitely see the difference between 25 and 50 fps... even 24/25 fps and 30 fps don't exactly look the same.

The 60/72/75/... Hz (some screens could display 85 or even 90 Hz) of the Windows 95 epoch was the refresh rate of the CRT tube: the higher, the less flicker. Once you tried 75 Hz, you clearly didn't want to go back to 60 Hz (or at least, that was my experience).

i can feel 144-200hz. above that i cant tell anymore, but probably pixel response times arent good enough yet on consumer hardware to provide a real test to me. 60hz feels awful to me. side note, i can discern stutters at 144hz + when i take a deep breathe.

Do you actively practice being able to discern high frame rates, or is it a "born with skill?" I often wonder if FPS gamers self select for those who can discern high frame rates, which then drives screen sales. Do you attempt to increase your frame rate perception?

Do you find normal movies in the theater difficult to watch because of your "high frame rate?" If I could see gaps in 144 Hz, then it seems (totally imagining with math), like it would be the equivalent of a 4 Hz frame rate for "normal" eyesight. 24 Hz / 144 Hz ( 24 Hz normal movie) = 4 Hz. 4 Hz looks super choppy bad. Seems like it would turn into the Flash trying to watch a human movie.

Course, I asked colorblind people about colorblindness, and it was totally crazy all the different colorblindness types they talked about. So could be bad mental picture.

In the theatre no, but scrolling shots on a fast panel can be particularly bad. There is no smoothing because the pixel response times are fast. I perceive a reverse motion of scrolling shots. If there is a slow scanning shot, say from left to right, after each frame stops, my eyes trick me that the whole image moves back to the left about an 8th of its rightbound motion. Its very mildly annoying, but I still watch though. I swear i can hear the frames stopping.

Many people have noted my particularly small head. But my reaction time is average. So time perception and reaction time may not be related.

Thanks, that gives me a much better idea about the experience from somebody else's perspective. A blog post or something would be interesting, if you have one on the subject. However, I may be a rather limited audience. Apparently up above somebody's saying 500 Hz tends to be the cutoff, yet I suspect there are large portions of the population with significant variations.

Like with colorblindness/synesthesia, I'm constantly surprised by all these different people I talk to who experience everything differently. Would not have guessed it would cause reverse motion scrolling. The eye exams and charts always made it sound like 20/20 at "normal speed" was correct, and the only change from correct was bad. Sounds like y'all just look at something different.

What's really crazy to me is that when you watch any film in >24(30?) fps, it looks like trash. I suppose it's because we're used to higher fps being home video? I wonder if films will ever be accepted or made in higher fps. Maybe if VR films actually become a real thing.

Part of the issue with higher fps is that it should be balanced with a shorter frame exposure time, so motion blur matches the frame rate. The rule of thumb is shutter speed should be 2x the fps, so shoot at 30fps, you want the shutter around 1/60s, if you shoot at 60fps, you should use 1/120.

This means anything that adds or remove frames is going to quickly cause the motion to look unnatural or at least different from the original.

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