Shooting Cars against Green Screen
Published : 4th June 2005
I'm in need of some urgent guidance.
A drizzly weather forecast has forced our HD X-Games promo spot indoors (how un-Xtreme is that?). The dead lined producer's last minute idea is to shoot the presenting sponsor's shiny new car rotating against green screen so as to comp in fair-weather action of skateboarders flipping and jumping over the car. Whatever.
Anyway, I've never shot cars on green. It seems that it would be a green spill nightmare with all the reflective and transparent surfaces, no?
Keeping in mind the car lighting concept of "lighting the reflections", why would I want to surround half the car with a noxious green Cyc? Yet, it's done all the time with shiny spaceships and such I figure. Can compositing software render out such pervasive green spill? I assume a light coloured car would pick up more spill while a dark car may reflect more of the background, both problematic. Perhaps a red car is the answer?
I find myself wanting to keep the reflections clean by shooting the car against white (or black?) and have the effects team try to pull mattes off of the luminance difference. Is this a solution? Am I over-thinking this?
Of course, I will be speaking to the effects house in the morning to see what they can handle, but as this is coming up fast (tomorrow!), I appreciate any immediate feedback you all may offer. Thanks!
un X-treme DP, NYC
If you are shooting the car straight on and your can run your turntable slowly and it revolves smoothly and evenly (the same time for each rotation ) you can do a matte pass and a beauty pass.
Use white Cyc car studio and a moveable green screen.
With the matte pass, mask off all the green screen except enough to give an edge of green so that you can garbage matte the rest. Only light that area. Film a complete revolve. This will provide you with your Matte. You will get surprisingly little reflection, especially if the camera is at a fair distance - 30ft or so.
Remove the green screen for the beauty pass and light the car off the walls etc for a sunny day, but remember to add some hard "sun" light.
This is really a motion control technique but, because the turntable is running slow, you can more easily match the beauty position to the matte position.
Speed the result up in post.
Interestingly, I did a car job last year where I used rear projection for the background behind the car and reflections on the car.
One of the scenes was a snowboarder and you saw his reflection going over the car in the windows and it looked totally believable.
The RP screen was 30' by 20' and the projector was a 6000 ansi lumen Christie with the replay slowed down and the Camera under cranking for exposure.
RP screens tend to reject off-axis light so you can light off large flats around the car. A large (10'x30') overhead Chimera also works well for this.
Isn't it natural to have the surroundings reflect off the car?
The key to a good composite is to have elements of the matte as well as the live talent to interact. --i.e. shadows and reflections-- The main question is what composite base (hardware) will you be using for the composite? Is this a video shoot, or a 35 shoot transferred to video? In both cases I suggest shooting screen corrections and/or matte passes. Shoot the green screen(backdrop) without the car, shoot the car on the green screen(backdrop), then remove the green screen backdrop and shoot the car on the white Cyc of the stage (the camera position/frame must remain constant!)
Richard W. Gretzinger
Director of Photography
I would also look into shooting blue screen instead of green since the blue reflected in the chrome and glossy paint wont be as offensive and wonâ€™t need as heavy of a removal effort that may turn some colors warm.
The blue reflection can feel natural (like blue sky). And blue generally has less spill (although the mattes will be a bit noiser), but it does require a little more effort to light.
So much of it depends on the specifics of the shot itself, the compositor & the software. You may well be laying in white bounces or black negative fill wherever you can (in the reflections) and maybe even using some dulling spray or chapstick on the chrome.
I think some of the best advice is the matte/beauty pass if its possible on your shoot.
LA based DP