GreenScreen, 3D integration, need Advices

[NNois]

Hi,
I'm in the case of the small team who is growing on a big project... As i'm a professional, i'm not aware of some common techniques used in film production.

Actually the project is base on Actors filmed on a green screen. So far so good but, some shoots needs some serious 3d integrations like:

- A guy driving a car with a full 3d env
In your opinion, do we even need a reel car as we have i think to model the 3d car and render it to get proper reflections/lights on it

- A guy on a beach, the beach is full 3d
In your opinion, do we need sand ? as we need the guy to make some sort of footprints on it.. Would it be more difficult to blend it correctly than even not using real sand ?

Well I have a plethora of question like this but this ones are the hard one i think

Cheers

[julius]

difficult to help with such a few infos and without seeing the footage...

It depends if you're confortable with ICE and/or other solutions too...

[FXDude]

Is all or most footage already shot?

For guy on sand,
he can have his immediate environment real which can help with integration, but you have to be sure about the final ground look, and will have to very closely match it in 3D lookdev along with lighting of course, but can still be more convinient than extracting shadows and making ground contact look seemless without too much involvment.

Or you can choose to have it digital, in which case you would then need to extract the contact and other shadows from the green screen, using the general key itself to focus only on the different shades of green, and probably at least rough rotos would surely apply, and since then dealing with slight luma variations, not only spacial but temporal noise reduction often helps alot.

Sometimes it may be beneficial to shoot it completely fixed and add camera motion in 3D (for handheld motion or not) in which case a clean plate from which you can extract difference mattes can help enormously.


For guy in the car,

Whatever he touches can be real (steering wheel, seat), and the car itself could not only easily be digital, but would almost have to be for all reflections and things.



If shot with a moving camera, you need well enough defined markers (in a similar but different green) to track the camera (if not motion controlled)


Otherwise Sound like a great project! are you free to say what kind of thing it's for?

Cheers,

[NNois]

Hi, such a few info, because the footage don't exists. The project is in a final dev phase where i'm taking tech in consideration before making final decisions about the storyboard...
I'm talking here because we need to shoot them right ;-)

FXDude, thanks I think we are on the same page, there's no voodoo tricks and we have to make it all 3d but the actors !
One thing by the way, i've done many greenscreen but i never thinked about a clean plate to extract the difference matte, seems genius ! Are you saying you can provide that to ultimate (or similar) to help the keying ?

About the project it's a tricky one, the output is mostly a 360 equilateral projection...

Thanks, I wish some more people can share their experiences in shooting footages on green ;-)

[Rork]

Maybe a thought or two...

Don't rely too much on getting clean plates at the shoot.
Due to the crazy paced day that comes with a shoot, there might not be enough time to shoot a clean plate.
Or they change stuff just before the shoot (e.g. lights), making it harder later to merge the two shots in comp.

Nuke has a pretty good keyer system for most things, even one that can get rid of parts of the screen to make a 'clean plate'. Works pretty good most of the time.

Be careful with 3d environments that will have a lot of reflections. That might mean that the actor's front/sides/back will also be in shot at some point, and if you only shot the one plate, you're missing the other ones. There might be multiple camera's needed to get your additional plates for comp later.

The shots are probably not static, so a proper marker setup for tracking later is a must. Don't go overboard with markers, as you might have a hard time painting them all out later ;)

And of course be sure to have a screen on site where needed, there's nothing more tedious than roto-ing out bits and pieces. And no, we can't fix it all in post, at some point crap in=crap out.

And regarding shooting stuff on set. Do it.
Even it's a small thing, it a physical thing on set and will look better in the shot afterwards.
Like the sand thing, I would shoot that for real (no 3D footsteps) and carefully comp that in the shot later. Just photograph the hell out of the props, so if needed you can redo/add to that afterwards. But you have textures based on the real thing and set lighting.
There's no substitute for the real thing, no matter how good the skills of the people are.

rob

[FXDude]

Good tips from Rob! And indeed taking clean plate shots adds one more thing to the sometimes long list of things to think about, and can be cumbersome if props need to be moved in and out of the frame. But if its just actors being shot you only need to roll a little bit before actors come in, perhaps along with grayball and/or color ramp board shots to calibrate things and match lighting to.

there's no voodoo tricks and we have to make it all 3d but the actors !
One thing by the way, i've done many greenscreen but i never thinked about a clean plate to extract the difference matte, seems genius !

There's no voodoo or magic there either, it's just like a simple blending equation like multiplying, and getting a "difference matte" is basically a merge in "difference" blending mode and making it grayscale, and adjusting levels.

it will also pick-up the green in things like skin color for instance, so it's not much use on it's own, but will also pick-up any subtle difference which can be used for say just the outlines of things (revealed by blurred key edge detections).

You can of course get quite excellent keys without any use of clean plates, but it can help alot for extracing subtle shadows right through all and any shading variations of the BG screen, even when great efforts are put on making it as uniform as possible.

Good luck!

[NNois]

Thanks,
So the actor in car will be the hardest one.. but each shots will be static. So i need to test this "clean" state and see if i can for example key the most of the car with this technique, but i have doubts need to test that monday ;-)

Thanks guys