DIY Underwater chroma / greenscreen compositing ?

J

Joe N. Obody

Member
I have some scenes with an actor underwater in a lake or river, any ideas on how one could cheaply DIY underwater greenscreening? Maybe rent the pool during graveshift hours at a local YMCA, do underwater green screening in the deep end of the pool? Say I drop a 8'x12' chroma muslin (or are there non-muslin green chroma sheets made of plastic or something?) along the wall of the deep end. Use underwater lights, waterproof housing for a DSLR camera (I already have that, cheap $200 unit)-- wouldn't i be able to do my own underwater chroma filming to then composite whatever i wanted? I figure less than $5000 for the hardware and rental of the YMCA pool?
 
You've outlined an incredibly difficult project. Why?

I would think that if the finished scene is a dramatic action scene you should shoot it as such. . . don't complicate it by injecting greenscreen. Why?

If you don't have any clear natural water where you are then go to Florida, or somewhere that does have clear rivers or springs. ($5000).

With green-screen you will have to deal with camera stability (not necessarily desirable for action), green-screen color accuracy, prop shadows (from background scene props), power, background/live action lighting and ratio match. It is a complicated project for even the most advanced production crew. And I don't think that I would trust an expensive camera to a $200 housing.
You better think this through a bit more.
 
Have you considered filming 'dry for wet'? I.e. the actor and background are nowhere near water, but you add filters (either in-camera or in post) to make it look like they are underwater. Obviously this does limit your shots a lot, e.g. you can't do a full body shot unless you suspend the actor from wires, but for close-in shots it can work well, and is a whole lot safer, faster and easier than doing it underwater.
 
Well, you'll have to deal with how hair moves underwater to fake it.

I have mused about the idea, never for a specific project. I'd think swimming pool in the daytime and not mess with lights - I'd rather hang a black frame (with a hole or slot if light needs to be directed) over a pool than a light.

The effect of water on color is an issue that could make keying hard. And getting a tight screen underwater may be a problem, though a butterfly frame might work OK. I could see it being done DIY, but I'd want a trained lifeguard who's a divemaster on hand. But getting a perfect green screen lit is hard enough on dry land...
 
Oh yeah, forgot to mention hair - short hair only for filming 'dry for wet' :) Similarly you need to avoid loose clothing or equipment which would swirl around if really underwater.

Michael's point on the effect of water on colour is also good - real water does tend to filter out (or absorb?) certain wavelengths, and the last thing you want is to lower the quality of your greenscreen key.
 
Don't use muslin underwater. It's going to soak up the water and relax in weird ways, change it's color to a much darker green, and generally give you a headache. Use Spandex instead. Rosebrand carries keying spandex. That'll make your life much easier, it will stay taught on the frame and when you pull it out of the water it will not weigh 5 times what it weighed dry.
 
Short hair underwater? Maybe a brush cut. Even 1/2" long hair moves and waves under water. Though you could shoot at a high frame rate with some wind machines or something.

Some particle stuff could go a long way towards selling it. Water generally blues-up your footage - I remember those disposable underwater cameras that used special film and had an orange lens. But there's plenty of info about shooting underwater, there must be massive forums (such as this) for scuba guys. Nikonos has been around for some time, after all..
 
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