Surely this makes your actors feel sick? And wouldn’t it make your motion blur look dashed and also cause artifacts at the edge of the mask if there’s a lot of motion?

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throwway120385 14 hours ago | parent | next [-]

You could strobe at some multiple of the sensor frame rate as long as your strobes are continuous through the integration period of the sensor and the lighting fades very quickly. This probably wouldn't work with incandescents but people strobe LEDs a lot to boost the instantaneous illumination without going past the continuous power rating in the datasheet.

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amluto 13 hours ago | parent [-]

You mean do strobe, strobe, strobe, strobe, pause, pause, pause, pause? I bet that's at least as bad as holding the source on for the first four intervals and then off for the latter four intervals.

In any case, if you actually have a scene bright for 1/24th of a second and then dark for 1/24th of a second, repeating, you're well within photosensitive epilepsy range. Don't do that to your actors unless you've discussed it with them and with your insurance company first.

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actionfromafar 12 hours ago | parent [-]

So, shoot at 240 fps and strobe set lights for 1/240s and backdrop for 1/240s.

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wlesieutre 9 hours ago | parent [-]

And if you want a slower than 1/240th second shutter speed, no you don't

	▲	actionfromafar 5 hours ago \| parent [-]
		Or... you frame blend in Fusion or go full hog in Nuke. ( https://www.nukepedia.com/tools/gizmos/time/vectorframeblend... )

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kibibu 14 hours ago | parent | prev | next [-]

Incandescent and fluorescent lights already flicker at your AC power frequency. Just gotta be higher than that

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amluto 12 hours ago | parent | next [-]

No.

Incandescent lights flicker at twice your AC power frequency -- to a decent approximation, their power is proportional to V^2. But this is input power -- the cooling of the filament is slowish and the modulation depth is low. Most people aren't bothered by this.

Fluorescent lights with old or very crappy "magnetic" ballasts flicker at twice the mains frequency, with deep modulation. The effect on people varies from moderate to extremely unpleasant, and it's extra bad if anything is moving quickly (gyms, etc). There are even studies showing that office workers perform worse under such lighting even if they don't experience personally perceptible symptoms. The effect is so severe that people invented the "electronic ballast", which flickers at much, much higher frequency and avoids low-frequency components. Phew. (The light might still be a nasty color, but the temporal output is okay.)

"Driverless LEDs" are deeply modulated at twice the mains frequency. These are very nasty.

If you actually have a light that flickers at the AC power frequency (certain LED sources in a two-brightness diode-dimmed kitchen appliance fixture will do this, as will driverless LEDs with certain types of failures), then it's extra nasty.

There are plenty of people around who find (depending on the actual waveform) 60Hz flicker intolerable and 120Hz flicker extremely unpleasant. And there are plenty of people who can often perceive flicker under appropriate circumstances up to at least several hundred Hz and even into the low kHz with certain shapes of light sources. You can read up on IEEE 1789 to find a standard based on actual research on what lighting waveforms should look like.

The effect of 120 Hz flicker is bad enough that energy codes in some places (e.g. California) have started to require that LED sources minimize this flicker, but, sadly, it's poorly enforced.

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kibibu 9 hours ago | parent | next [-]

Hey thanks for clearing this up. I had no idea that CFLs and fluorescent lights with electronic ballasts now flicker at ~ 20kHz.

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SoftTalker 10 hours ago | parent | prev | next [-]

The fluorescent light strobing is why you often see fluorescent tubes in pairs. They will be wired in opposite phase to cancel the strobing.

	▲	tlb an hour ago \| parent [-]
		I think the total light output of each bulb in the pair is the same at all points in time, but the orange-blue gradient is reversed. So when one is orange at one end, the bulb beside it is blue at that end. IIRC, the end that's negative looks orange, because the electrons emitted from the filament haven't gotten up to speed yet and can't ionize the mercury atoms at that end to the highest states. If you didn't do this, you'd see 60 Hz strobing when you looked at one end.

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toss1 10 hours ago | parent | prev [-]

Also, the human eye sees flicker much better at the periphery than in the central area. The Rod receptor cells respond more rapidly than the Cone color-sensitive cells, and the peripheral vision is also more tuned to quick motions (much advantage in having faster detection of peripheral motion, so positive selection evolutionary pressure).

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13 hours ago | parent | prev | next [-]

[deleted]

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joecool1029 13 hours ago | parent | prev [-]

phosphors and capacitors are a thing that mask that, so is high frequency switching way above this rate…

Anyway, an old HN submission I still use when buying light bulbs: https://news.ycombinator.com/item?id=14023196

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actionfromafar 13 hours ago | parent | prev [-]

Feel sick? Possibly. People are more or less sensitive to imperceptable flicker.

Artifacts?

I bet that can be remedied by interpolating a new frame between every mask frame. Plus, when you mix it down to 24fps you can introduce as much motion blur and shutter angle "emulation" as you want.

Motion blur can also be very forgiving. You are more likely to notice artifacts in still or slow moving scenes and then the problem goes away.