Why does 30fps+BFI look as smooth as 60fps on my plasma

[pneu]

So I thought I knew all there was to know about motion resolution from reading about it over the last 10 years or so, then today I'm looking at this testufo pattern on my 60hz Samsung plasma and I'm noticing the 30fps+BFI is looking just as clear and smooth as the 60fps without BFI, and no "double image" effect either.

Like, what? There's only half as many images, it should at least have jitter due to the lower number of unique frames. I thought this can't be real, must be a fake "simulated" test like the simulated gsync ones.

My new phone has a 120fps video recording mode so I recorded the screen to see what's actually being displayed and sure enough the 30fps+BFI ufo is only showing 30 unique frames - it fades to black over 4 frames (4x30=120). And the 60fps one is showing 60 unique frames - the ufo moves forward every 2 frames.

Are you telling me this whole time we could have been getting 60fps CRT-like image with only 30fps rendered if the display is impulsed in just the right way? Really?

[RealNC]

Are you telling me this whole time we could have been getting 60fps CRT-like image with only 30fps rendered if the display is impulsed in just the right way? Really?

30Hz flicker would be intolerable. It's fine with a small UFO, but if the whole screen is running at 30Hz BFI, it's not so nice anymore:

EPILEPSY WARNING - 30Hz HIGH CONTRAST FLICKER

https://www.youtube.com/watch?v=buLbnUAiFgQ

Most monitor vendors are even afraid to support 60Hz BFI or strobing, let alone 30Hz.

Other than that, yes. 30Hz BFI looks as clear as 60Hz non-BFI. Same as with 60 BFI vs 120 non-BFI, 120 BFI vs 240 non-BFI, etc.

[pneu]

Are you telling me this whole time we could have been getting 60fps CRT-like image with only 30fps rendered if the display is impulsed in just the right way? Really?

30Hz flicker would be intolerable. It's fine with a small UFO, but if the whole screen is running at 30Hz BFI, it's not so nice anymore:

EPILEPSY WARNING - 30Hz HIGH CONTRAST FLICKER

https://www.youtube.com/watch?v=buLbnUAiFgQ

Most monitor vendors are even afraid to support 60Hz BFI or strobing, let alone 30Hz.

Other than that, yes. 30Hz BFI looks as clear as 60Hz non-BFI. Same as with 60 BFI vs 120 non-BFI, 120 BFI vs 240 non-BFI, etc.

Thanks that makes sense.

I am still shocked that 30fps could look as smooth as 60fps.

I had always thought that low frame rates would have inescapable "jitter" due to the lack of images per second.

I did not know that human vision could be tricked into making 30fps look as smooth and clear as 60.

Well, now I know

Now I do have one unresolved issue: I read CRTs have a very short duty cycle. If I recall someone said the duty cycle of a CRT is only a few milliseconds out of the 16.7ms total, and that's why they flicker like hell. This is a considerably shorter duty cycle than the 50% duty cycle of the 30fps+BFI ufo. So does this mean 30fps on a CRT looks smooth like 60? Because I don't recall it being that way, and there are anecdotes saying 30fps on a CRT has the double image problem, which is the same problem the 30fps without BFI has.

What's the deal?

[RealNC]

Now I do have one unresolved issue: I read CRTs have a very short duty cycle. If I recall someone said the duty cycle of a CRT is only a few milliseconds out of the 16.7ms total, and that's why they flicker like hell. This is a considerably shorter duty cycle than the 50% duty cycle of the 30fps+BFI ufo. So does this mean 30fps on a CRT looks smooth like 60? Because I don't recall it being that way, and there are anecdotes saying 30fps on a CRT has the double image problem, which is the same problem the 30fps without BFI has.

What's the deal?

CRTs don't use BFI. They are inherently rolling scan displays. As a result, some part of the image is always visible, as the scan area (a single scanline) scans out the image top to bottom. Combined with phosphor decay, which makes the flicker smoother, it means they flicker less, not more, even if the frequency is the same. Rolling scan + phosphor decay is just easier on the eyes compared to instantaneous BFI or backlight strobe.

On how that looks like, see the videos I posted here:

viewtopic.php?f=4&t=13605&p=106791#p106791

Since there's no BFI, 30FPS on a 60Hz CRT does have a double-image effect, since each frame is scanned out twice. You'd get the same effect if you view 30FPS content on a 60Hz BFI display (which is running at 120Hz but half of the frames are black.)

[pneu]

Yes that's why I used the term "duty cycle" instead of BFI.

I had already seen that slowmo footage of CRT scan when those videos were originally posted way back when but I'm not sure it is entirely representative of what you would see because of the camera settings. I'm pretty sure the scanned line doesn't immediate disappear like in the second video from Efectum Channel. I think the phosphors remain glowing for a while like in the first video but even that may not properly represent the actual duty cycle.

Anyway I understand why the double image - the double scan.

[pneu]

I guess I still don't understand why the double image with double scan - is it due to eye tracking? I'm looking at the 30fps ufo right now and I'm trying not to track it but then obviously I can't see if it has a double image

[thatoneguy]

Now I do have one unresolved issue: I read CRTs have a very short duty cycle. If I recall someone said the duty cycle of a CRT is only a few milliseconds out of the 16.7ms total, and that's why they flicker like hell.

Depends on the phosphor being used. 60hz on a consumer CRT TV won't flicker as badly, especially at bigger viewing distances. You do get worse motion though.

16.67ms is for 60hz. For 30hz like in your use case it's ~33ms.
With an unlocked tweakable strobe you could probably get a happy medium where the flicker isn't so bad(especially if you lower the brightness a touch) but you won't get amazing motion, just better than regular sample-and-hold 30fps.

Here's a thread of a guy called zone74 who tested 24fps@24hz on a PC CRT Monitor.
Check out zone74's posts here
https://hardforum.com/threads/24p-playb ... n.1836881/
He says that 24fps@24hz on a CRT Monitor looks like interpolated 24fps on a modern display but without interpolation artifacts.

[RealNC]

I guess I still don't understand why the double image with double scan - is it due to eye tracking? I'm looking at the 30fps ufo right now and I'm trying not to track it but then obviously I can't see if it has a double image

At 30Hz BFI why would it have double image? Watch it at 60Hz BFI (meaning 120Hz with half the frames black.)

[pneu]

At 30Hz BFI why would it have double image? Watch it at 60Hz BFI (meaning 120Hz with half the frames black.)

On my 60hz Samsung plasma I don't get a double image on the 30fps BFI UFO (the UFO has 2 legs) but I do get double image on the 30fps UFO without BFI (it has 4 legs) and like you said that's due to it being double scanned or in the case of plasma double flashed or however it builds its "subfields".

So I'm still not clear why the double image. I'm not sure why flashing it twice would cause us to see double image with 4 legs on the UFO. I mean obviously it does, so there's some reason for it, I just don't know if it's due to eye tracking or something else.

[RealNC]

On my 60hz Samsung plasma I don't get a double image on the 30fps BFI UFO (the UFO has 2 legs) but I do get double image on the 30fps UFO without BFI (it has 4 legs) and like you said that's due to it being double scanned or in the case of plasma double flashed or however it builds its "subfields".

So I'm still not clear why the double image. I'm not sure why flashing it twice would cause us to see double image with 4 legs on the UFO. I mean obviously it does, so there's some reason for it, I just don't know if it's due to eye tracking or something else.

It's how our brain works. Simple as that So you could call it an optical illusion if you wanted. Same with motion blur on sample and hold displays. There is no blur whatsoever. The image is crystal clear. But our brains generate blur unless frames are flashed in and out.