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Crowd Duplication Tutorial – by John Kennedy

Resources_Post_127 - VFX Crowd duplicationVisual effects artist John Kennedy gives a practical guide to the commonly used post technique, crowd duplication.

One little trick that compositors get asked to do more and more these days is crowd duplication and I’ve illustrated this with a favourite example from a few years back: Robert Quinn’s Dead Bodies.

In theory it’s pretty simple. You take fifty or so extras in a group, shoot them in different positions around your shot and layer them all up to give the illusion of hundreds of people.

It could be any open space: a football stadium, a train station, a concert or a rally. In this case, it’s the back tiers of an auditorium. The key thing is to divide your shot into imaginary ‘blocks’ that you populate with each ‘instance’ of your crowd. You then get them to remove/change jackets, clothing, caps, tie hair up, let hair hang loose, etc. and place them in the next ‘block’ or layer. And so on, until all the blocks that make up your shot have been filled.

The compositor takes each layer and places them over each other. Obviously, the empty space around each action needs to be cut out to allow us to see through to the action behind or around it. The entire picture is built up and, hey presto (it’s not really that quick!), you’ve got a crowd of perhaps several hundred people.

The Golden Rules

Even if you’ve done it before, get your artists and effects people involved in helping you shoot this and don’t forget to cover the following:

  • How close are you to the crowd?
  • How long is the shot?
  • Is the camera moving? A moving camera will vastly increase the amount of work required in making the crowd-duplicated shot work convincingly. The only real way for this to work practically and effectively is by using a motion control rig.
  • Use as many tricks as possible to change your extras’ appearance between takes. You don’t want your audience spotting doubles.

Then, of course, there’s CG crowds but I think that’s for another day…
This article first appeared in Issue 127 of Film Ireland Magazine.