Green screen question

[lou4uandme]

To my surprise, I just received a over the shoulder 2 shot on green screen with a rack focus.

The green screen does go in & out of focus.



So My question is,

Is this ok or a nightmare? I never pulled a key with a rack

[tleisher]

Never done it either.

Sounds like a pain though. At the very least you may have to roto the out of focus people, blur the matte at the edges and then use that... but hey maybe it'll be easier then that. Only way to find out is to try.

[aaronber]

It completely depends on the shot. What does your shot look like (can you post some pics)? If you have a pretty clean greenscreen then it might not be so bad or the typical core/garbage matte approach might fall apart during the rack focus causing you to transition and blur between two separate keys.

[alexandru]

in a perfect situation there should be absolutely no problem. take it like this: if the screen is completly uniform and there is absolutely no spill, it should be rather easy to key. of course ... you'll never have this perfect parameters, but the closer they are to this, the easier it would be.

[bogenmichael]

I might be remembering wrong but two different keys and animate between them. One for each side of the rack.

Maybe?

[tleisher]

I might be remembering wrong but two different keys and animate between them. One for each side of the rack.

Maybe?

That's a very good idea.

[Junx]

I would just do a regular key, and then play with some edgeblur keyframing when it pulls from or towards the subject being out-of-focus. But thats my theoretical view, never really done it

[dcvfx]

the 'additive keyer' technique should solve such problems.

[lou4uandme]

Hi guys!
Thanks so much for your input.
No, I don't have the footage yet (2 more days) but I will fill you in on the project.
It was shot on the 5D, with an 85mm lens. It was shot outside on a sunny day. The screen had an exposure difference less than 2% at the most . (which was really nice) I "think" the screen should produce a good key.
Again, I had no idea the DP shot a rack focus.

I do have another question:
What would be the "easy" way to match this rack focus? I mean, its not like I have a reference of the background going in & out of focus. I have only a green screen. Am I going to have a problem matching the rack without a reference?

[Tagger]

what i usually do is, if there are points on the greenscreen.
Stabelize a point, just take a frame with the most focus, freezeframe it, and then put a defocus beheind that and try to match the focus of that dot throughout the animation. Use those settings for the plate.
after that you can still play with the values but this puts you in the right ballpark.

quick and dirty...

[lou4uandme]

That sounds great. You're the best!
I will try that THANKS

[alexandru]

yup .. always choose an empty region on your screen, one that would be very easy to garbage matte, and place a shape (like a square). not sure a point would be enough. with an 85mm lens, it might get all blured out, try something bigger. also don't forget that not everything is on the green screen's plane .. most of the stuff are further back. just shoot some reference to see how defocus works over distance and try to replicate that look. good luck with your work!

[aaronber]

I like to go out into the real world and take some reference photographs with a similar lens and lighting conditions for what you want to put into the background. In a perfect world you would be given some concept art or tests for what needs to be composited back there and what it would look like, but that doesn't always happen.

I think what alexandru said about distance is probably the most important thing and probably makes the whole point of matching to out of focus dots on your greenscreen kinda pointless. Your greenscreen may be ten feet away but what you are compositing may have elements as close as two (or even in the foreground) and as far as 5000 feet. Matching the focus blur at the depth of the greenscreen might not be the right thing to do. The dots in your background probably help with matching some 2D movement for your background so they are still useful.

[lou4uandme]

Thanks, I am still waiting for the footage to come in.
When I get it, Do you guys mind taking a look at it when I get it?

[alexandru]

if it's alright to post it on the net (no contractual or copyright issues), sure .. or at least i'll take a look.