Dirt adds realism to CG creations

Schmutz makes visual effects more convincing

The latest and greatest CG creations for film are borne from their digital wombs so perfectly and pristinely that they’re nearly unbelievable — and that’s just the problem.

They lack the scratches, gouges, wear and tear, traces of grease and grime, even surrounding haze that every object in the real world would have.

So visual effects artists have had to become digital Pigpens, leaving a dirt trail in their wake, to make their creations more convincing.

In Warner’s “I Am Legend,” for example, the human race has been all but wiped out by a virus, and Will Smith is the last man in New York. The city is going back to nature, so the CG images of familiar buildings needed weathering and aging.

“The sort of visual effects lens we look through doesn’t have the physical, mechanical imperfections of the camera and doesn’t capture the same kind of depth or atmospheric layers,” says Janek Sirrs, a visual effects supervisor on the film. “We call that process ‘sweetening’ when you take the shot and add bits of dust and things so it will fool the eye.”

All that dirt, smoke, haze and grime — let’s call it schmutz — was an important part of the look of “Transformers” as well.

“When we were working, (helmer) Michael Bay kept saying to mess things up and make them look gritty,” says Scott Farrar, visual effects supervisor on “Transformers.” “You need to be able to make it look like they’re really there and that there’s some kind of believable atmosphere between Optimus Prime and the actors.”

Layering in all that schmutz isn’t something to be fobbed off on vfx interns, either. “If there was a button that you could just push and have it all done, that would be great, but that’s just not how it’s done,” says Farrar. “Adding touches of dust and haze is a real art because small changes ultimately make all the difference. You have to be really good to know how to do that.”

Some visual effects supervisors use both digital and photographed “live-action” dirt and grime elements to make their CG elements real for the viewers. When they do, the in-camera elements actually help with their digital effects later on.

“If I can shoot something on set and get that lighting information, then everything else I do afterwards is easier,” says Patrick McClung, visual effects supervisor on “Live Free or Die Hard.” “For one scene, we hung a helicopter shell on set and drove a car right into it. It was my job to add blades, paint out the wires and add dust and some elements of the explosion later, and having the light information on those pieces makes that a lot easier.”

Tim Burke, visual effects supervisor on “Harry Potter and the Order of the Phoenix” always likes to use both digital and practical, in-camera effects.

“A specific example,” says Burke, “would be when Bane (the centaur) is attacked by Umbridge and falls down the slope on the forest set. For this we shot additional dirt, dust and clumps of earth being kicked up separately and then used them to bed the CG centaur into the plate.”

Oddly, even digital dirt and grime runs the risk of being too precise to look real.

“What we’re doing is actually very lightly added,” say Jim Berney, who is a vfx supervisor alongside Sirrs on “I Am Legend.” “We were trying to add some haze to scenes with our dog and our creatures, and it ended up looking really corny for a long time because we’d been too elaborate. Finally we realized we had to keep it as simple as possible for it to look right and real.”

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