What is that for? How Avatar The Way of Water controls light underwater for performance capture?

James Cameron learns from his mistakes on The Abyss (1989)

I love Avatar the way of water it's a beautiful film painstakingly assembled that transports you to an incredible fantasy world, but what I love the most is the innovation and problem-solving behind it. One thing that caught my attention with these white balls or beads floating above Sigourney Weaver. The production posted this photo on Twitter of the actors floating among these balls and then explained that the layer of white on the water's surface comprised of floating balls that prevented lights from interfering with underwater filming.

Source: Twitter

Avatar 2 is the first feature film to attempt underwater motion capture and when pioneering a new technique unforeseen problems will always arise. One of the problems the production had was the way light behaves as it enters the surface of the water. They needed to use very powerful fixtures to prevent the loss of intensity as light travels through water however as the surface of the water moves it grades distortions known as caustics. Caustics are the distortions caused by light as it reflects or reflects off of a curved surface or objects like light moving through a drinking glass.

Source: Blade Runner 2049

The motion capture system is optically based meaning markers are photographed by hundreds of cameras the caustics like tiny random reflections in a mirror confuse the cameras and cause false markers. To solve this problem they covered the tank with a four-inch layer of white balls they would then shoot the lights from above the tank into the balls which would diffuse soften and spread the light evenly inside the tank.

This would thus tame the caustics this was not the first time James Cameron used this technique to control light for underwater filming in his 1989 feature film The Abyss. He used black beads to effectively be able to shoot day for a night in the giant tank these beads would block the light coming from above the water so it would look like they were deep, deep in the ocean. You might be asking yourself why they didn't use a tarp or diffusion material instead of these beads one of the main answers is safety with the balls or beads the actors and crew can just pop their heads up above the water without getting caught in the material like a fishing net. An interesting side fact they use these black balls on bodies of water situated close to airports to prevent birds from nesting there and causing birdstrike as the planes take off.

Diffusing light with these white balls is only one of the many fascinating Technical Solutions that brought us the film Avatar the way of water.

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