Adding shadows to a projected plate for relfections.

[Justinoman]

Say Im projecting a plate for a ground plane I am using for reflections on my subject. The subject should be casting shadows on the groundplane and that should show up in the reflections(or even lighting if your kicking up bounced light). You cannot achive this currently. Currently if you want the groundplane used for relfections to have a shadow, you need to light it. If you light it, you lose the 1 to 1 color from the plate.

The material wrapper seems like the obvious choice, but it can not do what I need. It is only good for generating rendered shadows, not relfected shadows.

I need to be able to reflect a 1to1 plate (self illum 100%, light material, surface shader ect.) But also for that relfection to contain the subjects shadows that would cast on the object I am using for reflections (the ground plane)


Justin

[kweechy]

My current workflow is to render out a matte shadow pass of your object affecting the plate. Take that back into Nuke and correct the plate with it so the shadow is baked in. Render that out of the compositing suite and then pipe it back into Maya as your new plate projection.

[Justinoman]

Yeah but that only works if the shadow on the plate has enough definition. There are cases where the camera is at such an angle that the cast shadow is a thin sliver. But the reflected shadow is not. Also it would be way cooler if you didnt have to prerender every time the animation changes.

[joconnell]

The sneaky guys in frame store do a great trick with this - They light their object that they're integrating to whatever level they want, then put a white material on the ground plane they want it to sit on. Next they assign a white material to the ground and do a texture bake of the ground plane - this gives them the plain white material affected by whatever amount of light is in the scene. So say for example your lights might give it a slightly blue tint or whatever it is. Lastly they put on their projected background again, but they use one of the little maya math nodes to take the texture baked white texture away from the projected background. They're using the white texture as a way to find out how much light falls in the scene, so that when their live action texture gets lit by the scene lights, they can remove the extra amount of light that gets put on to it by the scene to give you the original look of your projected background but with correct shadows. Sneaky!