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Children of Men effect?
I was watching the making of the film…and was curious;
In the opening when the coffee shop explodes, there is a bunch of effects including advertisements playing on the buildings in the background.I am curious with everything added to that shot….why does only the bus have green screen on it? Is it because it is moving? Why not drop green cloth anywhere else?
Any help appreciated,
Aat 6:30 you can see what i was talking about:
https://youtube.com/watch?v=4A55xTYXMpI
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6 Replies
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My guess is because the explosion happens right in front of it.
I would imagine that the signs on the buildings are easy to track and most of the objects that pass in front of them would be relatively easy to roto. However, since the explosion has a bunch of particles and debris that obscure parts of the sign, it would be next to impossible to roto and easier to key it.
Hundreds of sq feet of greenscreen is probably not cheap either.Just my guess…
Erik
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I agree. That sounds reasonable. But the most impressive thing about this movie are of course those looong takes, and the most impressive of all is the scene in the car. Just… wow…
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[Empathetic1636] “I am curious with everything added to that shot….why does only the bus have green screen on it? Is it because it is moving?”
Yup. Because the bus is moving you’d want to be able to track the part of it where the video plays. And since this area is independently shaped from the bus, it’s best to create an area for tracking. I doubt that the green area was used for keying – more for tracking purposes. Once tracked, one could use the perspective tracked points to create mattes.
They would also have to track two different rectangular shapes to crete the effect that you see. Some simple extrapolation of the tracked data would yield the numbers for the two overlapping tracked areas.
The buildings are stationary and the area where video is to be composited is essentially shaped according to the building. So there is no need to have additional tracking information.
Cheers
Roland Kahlenberg
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Wow!
Thanks for info…..I knew I would be able to find answers here.
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Thats a really cool making of video… especially the scene with the car is amazing!
For the explosion scene I think they would have used the green for keying. The buildings aren’t moving but the camera is handheld and was probably quite shakey (dunno how much of the shakyness was added in post), but I’m sure still the buildings would need to be tracked as well – but you don’t need green for that, just any highcontrast corners. There are bits where cyclists etc. pass in front of the building, those would have needed to be rotoscoped.
As for the bus, you get a lot of debris passing in front of the ad, and to rotoscope that wouldnt have been feasible at all! So the corners of the green would be used for tracking and corner pinning, and then the green would be keyed with the corner pinned ad video underneath.
Yea if they did cover the buildings with green as well it would have been easier in post (no need for roto’ing the passing cars etc..) but it definetly would have ended up being more expensive! (balance the cost of that size chroma green fabric vs rotoscoping a few seconds of footage…)
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So silly me, I forgot that there is an entire write up on Children of Men in the July issue of Cinefex magazine.
In it they have a quote from the VFX Supervisor Frazer Churchill talking about the advertisements.
“We had greenscreens on buses…but no greenscreens on the buildings, which would have been too big too erect. We matchmoved the street and tracked in the ads with a little bit of translucency, revealing structures through the screens, light reflecting and layers of dirt…”What I find amazing is that that coffee shop/street explosion scene is actually two scenes and not one long take. According to the article they spent a lot of time matchmoving the two scenes together which were filmed on different days.
Interesting read.
Erik
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