DUAL ROLE VFX IN MOVIES

 A dual role  which is also known as a double role refers to one actor playing two roles in a single movie.

In most shots one person is the actor, the other is a stand-in/body double,but we need to use directorial techniques to make audience to never see the stand-in’s face.

Due to the advancement in technologies currently we have many methods for achieve actor multiple role sequences. 

Classic split screen technique using stop block shots
We need to film the scene with the actor performing in one part on the left and we need to film the same scene with the same actor in the other part on the right then we need to cut the two physical pieces of film together.The problem here is for each shot, there needs to be an invisible center-line the actors can’t cross so we splice the two pieces of physical film together.Most important thing to remember in this technique is the camera should be locked it should stay still.Any movement would destroy the split screen effect.This kind of locking the camera is also called stop block.

If we film the actor on the left part then right part should be hided by black matte and if we film the actor on the right part then the left part should be hided by black matte.

But the method is now easier by adding and adjusting the cropping effect with the digital editing software, you can simply layer the two shots and put a mask over clip in top layer . Since many post-production soft wares let you animate masks but mocha is the best and convenient software to rotoscope.

.i.e CGI-enhanced split screen: Same principle as the previous, but with newer technology. Film the actor twice and then combine them digitally. Digitally we can rotoscope so we can make actor to cross the center line. But even now camera should be locked it should stay still.Simply layer the two shots and rotoscope performer in top layer.If you plan to move the camera then motion control rig is the only option.Motion Control means motion that is very accurately, computer controlled, using electrical motors.We can repeat same movement of cameras again and again using motion control rig.  Roto scoping layers takes more time so it is usually done with green screen.

With motion control rig you can shoot the scene with the actor multiple times with different characters and combine them digitally.

CGI Import. We can design camera moves on CGI softwares, such as Softimage/Xsi and Maya and import it  to the motion control rig.But having the characters interact directly is still a little kludgy. 

CGI REPLACEMENT. We can now use current digital technology to put the actor’s face on the body double.

The good thing here is you can then have the characters interact — fight, shake hands, whatever — because you’re literally face-swapping the second person.That's how they did it in The Social Network with Arnie Hammer:The same face replacement technique was applied in "The Curious Case of Benjamin Button".

Same technique is used to replace face of stunt performer who work as double for an actor.

Powermesh tool in mocha provides good support for swapping face.It includes 12 new blend modes, improved render quality, motion blur, and new Grid Warp interface to bend/distort source elements.

You can understand how far the face can modified from the vfx woks of the movie Fan.
The vfx is handled by redchillies which is one of the legendary studios of vfx in india.Kindly search dcstechie yash to see this blog on google search.

Watch this video to understand more