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Advice for shooting outside against a green screen

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stan welks
Advice for shooting outside against a green screen
on Jul 7, 2015 at 3:49:05 am
Last Edited By stan welks on Jul 7, 2015 at 3:50:33 am

I want to shoot footage of a baby, and a dog separately, and composite both into After Effects making it seem like the baby is riding the dog.

My plan:
- use a c stand to hold a large collapsible green screen outside. I plan to use only natural lighting.
- place a rocking horse outside in front of the green screen (I haven't decided if it will be side profile or a front one)
- drape green screen fabric over the rocking horse, I will try to stretch it as much as possible with pony clamps
- put the baby on the rocking horse, and bounce her up and down
- separately shoot a dog running around in the same lighting
- key out the baby from the green screen in After Effects
- place the baby on the dog in After Effects

1. Any advice in general for what I'm trying to achieve?
2. Any tips for lighting that will work best to light my subject and green screen?
3. Any tips for maintaining scale when shooting video of the dog and baby? I'm guessing the dog is going to run at a distance from the camera farther than when I'm shooting the baby. I can control the shoot with the baby, not with the dog.

Thank you!

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Mark Suszko
Re: Advice for shooting outside against a green screen
on Jul 7, 2015 at 4:18:49 pm

Instead of a rocking horse, use a simpler form, without any obscuring neck and head. You can make that out of scrap cardboard and some 2x4's, or just an overstuffed duffel or punching bag, then drape that with the green cloth.

How I would do this shot would be to create a dolly track for one quarter to one half-circle. Starting with the baby head-on to the camera, shoot continuously, while dollying from the head-on position around to the side-on position, and around to the back, while an assistant grip moves the green panel to correspond to the camera view, and the baby-wrangler keeps baby's attention looking mostly forward. Might need to have the baby wrangler wear a green spandex body suit while working this shot. Heck, maybe you skip the rocking horse and just put the baby on the spandex-wearing wrangler:-) Tubetape sells those suits.

Some skate wheels or simple hardware store casters on the bottom of the butterfly frame holding your green screen can help make the frame easier to maneuver.

Repeat this shot as many times as the baby will tolerate, also doing the same shot with the baby's angle reversed, his back facing the camera, and ending up on the other side. Now you've captured a 360 view of him, more or less.

If the local park has a playground with a turntable or kick-operated merry-go-round, that might save you the need for the dolly. Spin the baby (slowly!) instead.

What this gives you is the proper body perspective to match whatever compass direction the dog is later facing. Using Adobe's new Morph Cut, blending between baby shot angles to match the dog's angles will be easier than it would have been a year ago.

People with a real budget would probably digitize the baby and create a model, put a saddle and doll with tracking markers on the dog, transferring the markers to the model in the composite. If you can avoid having to CGI the dog, it's a huge time saver.

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Blaise Douros
Re: Advice for shooting outside against a green screen
on Jul 7, 2015 at 11:23:08 pm
Last Edited By Blaise Douros on Jul 7, 2015 at 11:23:40 pm

I have a different take than Mark.

You need to first shoot the background plate of the running dog. Go through and find the take you like best, and then do your best to replicate the angle when you go to shoot the green screen; now, since you know what your focal length was when shooting the dog, you can use something similar for the kid. This may mean shooting on different days, in order to plan the second shot of the kid. You're going to have to worry about scale afterwards--the key is going to be the angle.

If you can, have your selected take on an on-set monitor with you. Put the kid on a rocking horse or sawhorse or whatever, and put that on top of a turntable. Someone needs to turn the turntable so that the kid's rotation matches the dog's as closely as possible. Remember, once you rotoscope the background out, you can control scale, vertical, and horizontal movement, but rotation is the one thing you can't control in post. I think it's also key to have the kid on a turntable, and not the camera on a dolly--if the dog makes a sharp turn, you want your turntable operator to mimic that, and the kid will sway in reaction to the turn.

As you said, you can control the kid shot, but not the dog. So why go through the trouble of shooting every possible angle on the shoot you can control, when it might be completely different from the footage you get of the dog?

Don't shoot this on a DSLR if you can help it. AVCHD or h.264 is going to make the chroma key difficult to pull; you need something that shoots 10-bit 4:2:2 in order to pull a clean key.

Make sure there are no shadows on the greenscreen, and that it's placed far enough back from your subject that the green isn't reflecting in their skin.

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Mark Suszko
Re: Advice for shooting outside against a green screen
on Jul 8, 2015 at 4:05:36 am

The farther back the screen goes, the larger it has to be, and large, outdoors, in wind, can be trouble. Just remember you don't need a *lot* of green around the edge,just a bare minimum and the rest you fix in post with a "garbage matte".

Ideally, you shoot on an overcast day. You might use another helper with a sheet of foil-backed styrofoam from the home improvement store as a reflector to fill in the front, but again, beware the wind. I would tip the green screen back a little bit, to catch even sunlight across the entire span. I agree about the codec choice and going 10-bit. If you have a color chip chart, do shoot a bit of that using the same setup, and use that for the initial color setup *before* you attempt keying.

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Aaron Star
Re: Advice for shooting outside against a green screen
on Jul 20, 2015 at 6:15:35 pm

Plus one to all the 10bit 422 video for compositing reasons.

You could also find a hilltop or roof top, and shoot against the north blue sky. A polarizer can help with darkening the blue contract of your sky background.

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Calvin Romeyn
Re: Advice for shooting outside against a green screen
on Jul 27, 2015 at 10:47:57 pm

I would actually recommend not using any green fabric on the rocking chair/whatever you put the baby on.

In my experience, you never get a good key off fabric that is folded or draped over things.

You usually just end up with lots of shadows and folds, which you end up having to roto, or crush your matte, compromising edge details. Not to mention all the spill you will have with having skin right against green fabric. Instead, I would just use a neutral colour like black or grey, and just roto all the parts that go over it. You will get more consistent edges, and maintain the natural skintones.

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