Retaining shadows with chromakey...?
I make language tutorial videos and I'm looking to do some fancy "hands" videos, where I set my camera up looking down on green baize card-playing mat, and then I explain some printed material, with the print changing dynamically under my hands, through the magic of compositing.
Now usually green-screen work means eliminating all shadows to maintain the illusion that the screen isn't there, so the chromakey effect is built under the assumption that that's what we want. However, I'm working with a virtual piece of paper here -- the green screen is a flat surface in exactly the same place the virtual flat surface of the paper is going to be. Because of this, the lack of shadows now breaks the illusion, rather than making it.
I've been looking around for a way to retain luma information from the keyed-out area, and apply that as a shadow in the compositing process.
Is there a straightforward way to do this?