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Keyed model dancing to camera flashes

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andrew donaldson
Keyed model dancing to camera flashes
on Nov 15, 2013 at 3:09:17 pm

Hi there bovine chums,

Firstly, what a horrible subject header i know. Sorry.

Im working on a job where we have a model dancing in front of a greenscreen.
That's all keyed fine and looking good.
We've got a stock movie of some paparazzi stlye camera flashes which is to be composited with said model.
Also fine. done.
I've got some VC Optical flares for added sparkle, etc so all is going good.

What i'd like to do is get the model's luma values to change when the flashes go off.
It doesn't necessarily need to be exactly in time, coz it gets pretty fast, but i wondered if an expression might do the trick? or pickwhip some max RGB value to a slider to something...

Anyway, I'll not waffle on for too long.

Can anyone point me in the right direction?

Many thanks, fellow grass munchers.

Andrew.


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Dave LaRonde
Re: Keyed model dancing to camera flashes
on Nov 15, 2013 at 3:43:29 pm

Hmmm... An expression can help you with the duration and frequency of the flashes, but the real question is, "does it have to look convincing?"

Here's the deal: it's not tough to jigger the footage to look overexposed for an instant. The thing that really sells a flash is where the SHADOWS fall as the flash goes off. Just set up a camera, roll on anybody, set off a strobe several times in a few different positions, then scrutinize the footage and you'll see what I mean.

How do you make the shadows? By masking the overexposed areas, and layering overexposed footage over properly exposed footage. For one frame.

I bet the model turns, moves and poses like all good models do. I bet those still photogs are intended to be in a few different locations. I bet the desired effect involves a few cameras, firing at different times, in a seemingly random pattern. Thus, you'd have to create a boatload of different masks for different angles.... it gets messy and complicated.

But if you really want to sell the shot, that's what it takes.

Dave LaRonde
Promotion Producer
KGAN (CBS) & KFXA (Fox) Cedar Rapids, IA


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andrew donaldson
Re: Keyed model dancing to camera flashes
on Nov 15, 2013 at 3:56:54 pm

Hi Dave,

Im sure im using one of your old Keylight tips on this job too btw! ;-)

I don't need shadows because its only been shot from the knee up and there's no reflective surfaces.

I really was looking for an expression to overexpose the shot when the flashes go off - that's a better way to explain what i meant.

should I shift this to the AE expressions forum?

Cheers,
Andrew.


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George Goodman
Re: Keyed model dancing to camera flashes
on Nov 15, 2013 at 4:26:25 pm

For clarity, are the flashes coming from footage or an effect in AE?


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andrew donaldson
Re: Keyed model dancing to camera flashes
on Nov 15, 2013 at 4:34:29 pm

Hi george,

They are a stock video file from istock.

The piece is only about 10s long, so i could probably keyframe what i wanted, but wondered if there was any super-pro tips out there!

Ta,

Andrew.


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Conrad Olson
Re: Keyed model dancing to camera flashes
on Nov 15, 2013 at 7:09:00 pm

Can you create a high contrast version of the layer with the flashes in? Crush out all of the blacks until all you can see are the flashes. Then you can take this layer, blur it, grade it, scale it, whatever, and add/max/screen it on top of your model. Then you have flashes whenever there are flashes.

You could even pull a key of your shadows, and use another copy of this layer set to max, to fill them in and keep Dave happy.

---

conradolson.com


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Dave LaRonde
Re: Keyed model dancing to camera flashes
on Nov 15, 2013 at 7:22:18 pm

I'd buy that trick with the shadows, but it sounds like the guy wants to have strobe flashes coming from several cameras, which implies a variety of different angles. I don't know if just one angle would cut it. It might. But then, it might not.

Dave LaRonde
Promotion Producer
KGAN (CBS) & KFXA (Fox) Cedar Rapids, IA


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Conrad Olson
Re: Keyed model dancing to camera flashes
on Nov 15, 2013 at 7:43:50 pm

Well if you use the layer with the flashes in, there will be light patches from different parts of the screen, so that will add a bit of directional light.

It's never going to be perfect Dave. I know it's good to strive for perfect, but as long as you sell the effect it's good enough. Flashing the whole layer should be enough to get the message across. Especially if you can lift the existing shadows, and it's quick.

---

conradolson.com


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Conrad Olson
Re: Keyed model dancing to camera flashes
on Nov 15, 2013 at 7:45:29 pm

Knowing what you need to do to make something correct is an important skill as a VFX artist. Knowing what you can get away with is equally important.

---

conradolson.com


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Dave LaRonde
Re: Keyed model dancing to camera flashes
on Nov 16, 2013 at 2:05:59 am

Yeah, I cheat a lot, too. I hear you.

But you never know: somebody may want it just picture-perfect. There's a person out there who probably thinks Lucasfilms-quality light saber duels are all done with expressions.

Dave LaRonde
Promotion Producer
KGAN (CBS) & KFXA (Fox) Cedar Rapids, IA


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Dave LaRonde
Re: Keyed model dancing to camera flashes
on Nov 15, 2013 at 4:38:10 pm
Last Edited By Dave LaRonde on Nov 15, 2013 at 5:32:17 pm

Um, are you SURE you won't need shadows?

Have you ever looked at a person -- shot on video, perhaps waist-up -- where a camera flash fired off in a different location than the videwo camera? At 45-degrees from where the video camera's located, perhaps?

Have you ever scrutinized the video frame of that flash? Before you say "I won't need shadows", I strongly recommend you take a look. Take a good, long look at the nose shadows. Take a look at the shadows cast by long hair partially covering the face. Take a look at the shadows cast by the chin.

Oh, and I just re-read this thread title: the subject's DANCING! Swinging arms around and such! Casting shadows! Another piece of the puzzle to consider.

Ain't nothin' like the real thing to teach you how to replicate reality.

Oh, and don't forget about the Inverse Square Law: if a light source is TWICE as close as a second source of equal brightness, its light falling on the subject is FOUR times brighter. Which means the overexposures can't all be the same, either.

And you thought this would be easy.

Of course, you can always blow off this quest for reality, and do whatever you want.

Dave LaRonde
Promotion Producer
KGAN (CBS) & KFXA (Fox) Cedar Rapids, IA


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andrew donaldson
Re: Keyed model dancing to camera flashes
on Nov 15, 2013 at 8:26:30 pm

Hi guys!

What an awesome topic this turned into!

Conrad, your high contrast suggestion sounds like a perfect solution for what I was after! Cheers!

Dave, you make some good points. I didn't even really think about the shadows on her face! D'oh!
the piece is only 10 seconds long and has about 15-20 cuts so its pretty quick.
we're not going for the ultra-realistic thing, so i suppose as long as i can make it look good!

And when I read your comment about DANCING! I laughed my ass off, it reminded me of the scene in Back to the Future: "1.21 Gigawatts!!! Great Scot!"

Anyway, thanks for all the suggestions guys!

Thank moo...


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George Goodman
Re: Keyed model dancing to camera flashes
on Nov 15, 2013 at 9:44:42 pm

I think what you need is an expression to link the flashes to the overexposure of your subject. The problem for me is that I wouldn't know how to extract the data since your flashes are derived from footage rather than an effect. There is probably some way to get the luma value of the flash footage into keyframes much like how you keyframe audio, but I wouldn't know how to do this.

If you can get that value though, you could write and expression that would tie the overexposure effect to the luma value of the flash footage.


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George Goodman
Re: Keyed model dancing to camera flashes
on Nov 15, 2013 at 10:03:44 pm

try this:

http://forums.creativecow.net/thread/227/20921

change the opacity value out for whatever effect you're using to get the overexposed look of your dancer. It doesn't help with the shadows, but hey, 1 problem down ... or close to


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