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Rolling shutter & strobe light


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#1 Artyom Zakharenko

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Posted 18 April 2011 - 05:12 AM

Hi all

You probably all know the rolling shutter issue with CMOS sensors...

So here's the thing.. Im shooting a club scene (like the Blade's opening rave scene) and i want to have a strobe light effect on screen, now, i know that if i'll use a strobe light they use in clubs, i'll get flickering light stripes jumping up and down all over the image...

My question is: Is anyone familiar with this problem and if so what's the best way to handle it? Is there a way i can get the same light effect but without stripes?

Shot to be made on RED, 120fps (120fps because i want it to be slow motion)

Thanks!! :)
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#2 Mathew Rudenberg

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Posted 18 April 2011 - 01:38 PM

So far I have found no way around this with strobes and the Red. Lightning Strikes paparazzi units are much better then any other flash unit I've tried, but they still give you a half frame 10 or 20% of the time.

The alternative is to use a non strobe type light with a fair amount of punch and to flicker it (through a dimmer board or by hand if necessary).

Mini-brutes (fay nine-lights) are pretty good for this since their small filaments lighten and darken fairly quickly - I wouldn't try to use a single big globe like a 5 or 10k.
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#3 John Sprung

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Posted 18 April 2011 - 02:59 PM

Shoot without strobes. Shoot reference stills with constant sources in the positions where you want strobes. Fake the strobes in post. Each flash is just a single hand-made frame.





-- J.S.
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#4 Jim Menkol

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Posted 26 April 2011 - 10:45 AM

Shoot without strobes. Shoot reference stills with constant sources in the positions where you want strobes. Fake the strobes in post. Each flash is just a single hand-made frame.





-- J.S.



Agreed with John. Adding the strobes in post is probably your best bet. I've heard that The Foundry's Rolling Shutter works pretty well, anyone have any experience with this plugin?
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#5 Jim Menkol

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Posted 26 April 2011 - 10:52 AM

Agreed with John. Adding the strobes in post is probably your best bet. I've heard that The Foundry's Rolling Shutter works pretty well, anyone have any experience with this plugin?



Sorry, just found the thread on the plugin:
http://www.cinematog...showtopic=49616
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#6 Chris Millar

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Posted 27 April 2011 - 05:07 AM

Agreed with John. Adding the strobes in post is probably your best bet. I've heard that The Foundry's Rolling Shutter works pretty well, anyone have any experience with this plugin?


it aint going to help with half a frame of flash though (unless it has a mode they've added recently ?)
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#7 Phil Rhodes

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Posted 27 April 2011 - 08:07 AM

I'm not sure how you could possibly do that.

First task, figure out which frames have flash on them.

From the 2D image you have of the scene, reconstruct a 3D model.

Using lighting information (which you must have extrapolated separately from the 3D scene), figure out where the light is coming from and other characteristics of the source.

Render that lighting into the 3D model of the scene.

Superimpose that light on the part of the scene that wasn't originally exposed.

Next week, the world on a stick - I wouldn't hold your breath.

P
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#8 Chris Millar

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Posted 27 April 2011 - 03:19 PM

Well, yeh - sure. But you could take a more 2d approach and do a statistical analysis of real world footage before and after flash - throw in some on the fly analysis of the flashed area and unflashed area of the frame - then apply your math to the remaining pixels...

You could have some modes for extreme circumstances (whatever they turn out to be)

Its only going to be one frame anyhoo right ? you could be relatively rough
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#9 John Sprung

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Posted 27 April 2011 - 05:47 PM

The thing is, it would be easier to do on a whole non-flashed frame than on a half and half frame.




-- J.S.
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