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Compositing a rooftop city scene

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Josh Brine
Compositing a rooftop city scene
on Sep 11, 2012 at 2:58:46 am

Ok, we shot a rooftop scene on our driveway. using a jib, we were emulating a rooftop, so we were blowing wind at our talent, this made the trackers on the greenscreen useless (lesson well learned)

however keying/roto(lots) is not the major issue, i feel confident i can seperate the areas i want to.

the real challenge is tracking.

It was not set up well to be a 3d tracking scene, there are no trackers 'off' the floor. so its really a 2dimensional image
from my understanding of 3d tracking. you need parallax and FG&BG and any other trackers you can to really give the computer depth to work with. this was not shot so. the camera is often gently craning forwards and backwards, with subtle jib movements that slowly shift the perspective.

Let me break down some of the challenges

the opening shot: the jib flies along the ground and then cranes up to reveal our talent standing on a 'ledge'

i use blender, and CS6

(not permitted to use actual footage, so explanation will have to do.

the floor is quite textured and possibly holds enough to get a few tracking markers down.

but i dont know 'what' to do with it.

i want to remove the ground where its flying across and create the face of the building. but using a planar tracker gives the wrong perspective,

3d tracking has no parallax,

is this something that a 2d tracker can handle?


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Darby Edelen
Re: Compositing a rooftop city scene
on Sep 11, 2012 at 9:41:54 am

From your description of the shot there may be enough information to solve for a camera (3D track).

Make sure that you exclude any moving objects (windblown hair...or windblown trackers) from the tracking.

Darby Edelen

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