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What's wrong with this motion blur


Heath Orchard

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50 minutes ago, Heath Orchard said:

So here's a couple stills pulled from the original clip that seem to support this. Notice the point sources read as sets of three as the camera is panning into position but once it settles for the take everything becomes one. But there is still no flickering anywhere. What's interesting is that we didn't see it on the day, which makes me think Mei Lewis has a point with the refresh rate of the monitor, which was a SmallHD 1703 P3x. 

Screen Shot 2021-01-16 at 3.33.28 PM.jpg

Screen Shot 2021-01-16 at 3.46.48 PM.jpg

Mmm interesting .. worth remembering..the perils of practical LEDS.. but what Tyler says is also true .. thousands of people are shooting with no film LED,s , Im sure I have many times on docs / corp shoots .. you would think this problem would be happening all the time ..

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I don’t know the Venice camera, but is it possible that it does multiple sensor read outs to extend dynamic range?

if so, it could create this effect, which in most circumstances is not noticeable.

This might be a question for the Sony engineers.

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So just to officially put this topic to bed. Phil was right the whole time. I sent a clip to a couple of true experts in motion blur, and while their initial reaction was a frame rate conversion problem, they ultimately came to the conclusion that it's the LEDs. And upon closer examination with them I agree 100%. At one point we started to believe that it might be caused a portable lantern my gaffer and I came up with that was essentially an array of NYX bulbs in a chimera lantern on a painters pole. Apparently these lights have an adjustable PWM (pulse width modulation) setting and we thought maybe that had been set to something that didn't play nice with our frame rate. An issue I've never encountered before and I was a little surprised to find out those bulbs had that functionality.

But that is not the problem here. In one of the final moments of the film there is a shot that is lit almost entirely by the NYX lantern and the problem is no longer there. It comes down to the LED string lights and it's clearly seen when the camera pans quickly and they all multiply. Tyler made a convincing argument that the background city lights were also multiplying, but as I looked closely at full resolution and even cross referenced the background lights from different takes, it's clear there is a normal motion blur happening in those sources or there are multiple sources giving the illusion of a multiplying effect.  So fortunately the NYX bulbs are still awesome and it all comes down to shitty mass produced LEDs aren't to be trusted. Duh. 

Thanks everyone for helping me get to the bottom of this!

-Heath

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2 hours ago, Heath Orchard said:

So fortunately the NYX bulbs are still awesome and it all comes down to shitty mass produced LEDs aren't to be trusted. Duh. 

Sounds like ya figured it out. Yea it's hard on the low-res jpegs, can't really see enough detail to fully get a good picture. I'm shocked it was the cheap LED's, I've used them a lot and never had that sort of a problem. Very very very odd. 

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On 1/20/2021 at 8:27 AM, Heath Orchard said:

So just to officially put this topic to bed. Phil was right the whole time. I sent a clip to a couple of true experts in motion blur, and while their initial reaction was a frame rate conversion problem, they ultimately came to the conclusion that it's the LEDs. And upon closer examination with them I agree 100%. At one point we started to believe that it might be caused a portable lantern my gaffer and I came up with that was essentially an array of NYX bulbs in a chimera lantern on a painters pole. Apparently these lights have an adjustable PWM (pulse width modulation) setting and we thought maybe that had been set to something that didn't play nice with our frame rate. An issue I've never encountered before and I was a little surprised to find out those bulbs had that functionality.

But that is not the problem here. In one of the final moments of the film there is a shot that is lit almost entirely by the NYX lantern and the problem is no longer there. It comes down to the LED string lights and it's clearly seen when the camera pans quickly and they all multiply. Tyler made a convincing argument that the background city lights were also multiplying, but as I looked closely at full resolution and even cross referenced the background lights from different takes, it's clear there is a normal motion blur happening in those sources or there are multiple sources giving the illusion of a multiplying effect.  So fortunately the NYX bulbs are still awesome and it all comes down to shitty mass produced LEDs aren't to be trusted. Duh. 

Thanks everyone for helping me get to the bottom of this!

-Heath

Thanks for the follow up.. so worth paying attention when using practical LED,s .. but you say its only happened when the dancers were moving quickly .. or there all the time .. ?

 

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7 hours ago, Robin R Probyn said:

Thanks for the follow up.. so worth paying attention when using practical LED,s .. but you say its only happened when the dancers were moving quickly .. or there all the time .. ?

 

Well, you'll only see it when there's enough motion to create significant motion blur, and it's subtle even then when you watch in full motion. I suspect this actually happens quite a lot, and people just don't see it because it's not massively objectionable. Also, if you're under a mixture of continuous and discontinuous lighting, it'll be less obvious. The clearest way to see it is often to whip pan across the scene and look at the lightbulbs - it should certainly be visible in a freeze frame, and you can sort of train yourself to see it in motion if you look at a few examples.

The other way to find it is to wave your hand back and forth quickly under the light. The motion will appear staccato and stroby under a light flickering at these sorts of rates. This is one of those things like rainbow strobing on single-chip DLP projectors that some people don't really seem to see, so get your eye in.

Another good trick is to get your cellphone out and stick it right into the light source so that it sees nothing but a blast of light and closes down its shutter timing; that'll provoke either venetian blind stripes, flicker, or some combination of the two, depending on the behaviour of the light in question. It's not completely foolproof but it can help you quickly recognise the most egregious problems, like so:

800px-CFL_flickering_visible_via_rolling_shutter.jpeg

lm7HG.jpg

Flickering_of_incandescent_bulb_visible_via_rolling_shutter.jpeg

1200px-Flickering_LED_lamp_visible_via_rolling_shutter.jpeg

P

 

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On 1/21/2021 at 7:05 PM, Phil Rhodes said:

Well, you'll only see it when there's enough motion to create significant motion blur, and it's subtle even then when you watch in full motion. I suspect this actually happens quite a lot, and people just don't see it because it's not massively objectionable. Also, if you're under a mixture of continuous and discontinuous lighting, it'll be less obvious. The clearest way to see it is often to whip pan across the scene and look at the lightbulbs - it should certainly be visible in a freeze frame, and you can sort of train yourself to see it in motion if you look at a few examples.

The other way to find it is to wave your hand back and forth quickly under the light. The motion will appear staccato and stroby under a light flickering at these sorts of rates. This is one of those things like rainbow strobing on single-chip DLP projectors that some people don't really seem to see, so get your eye in.

Another good trick is to get your cellphone out and stick it right into the light source so that it sees nothing but a blast of light and closes down its shutter timing; that'll provoke either venetian blind stripes, flicker, or some combination of the two, depending on the behaviour of the light in question. It's not completely foolproof but it can help you quickly recognise the most egregious problems, like so:

800px-CFL_flickering_visible_via_rolling_shutter.jpeg

lm7HG.jpg

Flickering_of_incandescent_bulb_visible_via_rolling_shutter.jpeg

1200px-Flickering_LED_lamp_visible_via_rolling_shutter.jpeg

P

 

Ok thanks sir .. another thing to look out for ..Im beginning to wish it all stayed fluorescent!!

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  • 1 month later...

In case anyone is interested in seeing this film and the freaky motion blur in action, San Francisco Ballet premiered it to the public this week as part of a benefit gala for their 2021 digital season. I think they pull it down after tomorrow. You can check it out here, https://www.sfballet.org/tickets/2021-season/leap-into-the-new-year/  scroll to the video at the bottom of the page and jump to 29:09. 

-Heath

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