A Three-Phase Operation in a CG Shot

Suppose you have a scene where a car enters a shot and then gets exploded and obviously you prefer using CGI rather than a real explosion, because having a real car exploded using special effects might take more budget than doing that in CG.

Now that you have decided to use vfx, you are faced with a three-phase operation. First is the normal phase, which of course is the normal car. Second is the transition, which is the explosion and the third is the aftermath, which is the damaged car.

Now if you are going to create such a scene in full CG and use all the elements generated by the computer, there are not much of choices for you, you just simulate an exploding car with dynamics and distortions, but if you want to create such a shot with the help of real filmed footage, you have two options: Either you make the first phase which in our case is the normal car in real and then use CGI to simulate the explosion and then aftermath, or you can use CGI for normal and the transition phase, and then use the real footage for the third phase, which means filming a real damaged car.



So which strategy you should choose when encountering such scenario is up to the details. If you have more focus on the normal car, for instance a guy is shooting out of its window, the car is drifting and it has smokes coming out of its tires, it’s more realistic to shoot that event in real, rather making it CGI and you go with first method. Now imagine there is a car heading towards the camera, and you can’t see the driver because of the environmental reflection on its front glasses and that’s it! No more visual details. And when the car explodes, you will be having a damaged car, a little bit of fire rising and maybe someone getting out of it while burning, with flames all over his body. In this case it’s better to use the second method.

In addition, another benefit of using the second method is that before exposing the element of surprise, the explosion, viewer’s eyes are not sensitive, so you can trick them easily, but after the transition phase they get more sensitive and the viewer will try to watch the shot more in details, so it is better to film the aftermath.

Overall if you have the equal elements for making the shot in full CG or making it totally filmed with special effects, the result might end up the same, but remember, most of the times making something hybrid, half real and half CG, is the best way to trick the eyes of the viewer.



Children of Men

Now let’s check a real example in a feature film. I’ve picked a shot in “Children of Men”, because it is not perfectly composited and actually you can detect the CGI, not being tracked well and as a result you can see this method more clearly.

There is a shot where the main character “Theo Faron” played by “Clive Owen” is running away from some shooters to a wrecked bus on a street. When he gets inside, a window breaks so he can see what’s happening outside.

For shots like this, you either break a real window with explosives, or you make it CGI. In this case it’s CG. Now about the two options we’ve discussed, either you keep the real window there and use CGI to simulate the breaking, and showing the other side of the window which is hard to create, or you can remove the window at the first place and put a CG glass there, track it with the bus and when the moment comes, make it broken and move it away so the viewer can easily see behind it, which has done here.




But if you watch the normal window closely before we go inside the bus, it is modeled bigger than the frame of the window so it is not located properly. Even with a glass not matching the size of the frame, a solution could be scaling down when compositing it with real footage or go back and size it down.

So remember which option you are going to use, because it is a key decision and could be a time savior or budget savior later on.


By Mazyar Sharifian
From Cubichead.com

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