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We do a lot of work adding cg elements to live action plates. One thing I like to use to create more realistic shadows is have the matte object recieve GI. This really created a nice fill in the shadows and looks very natural. However, there is one side-effect that happens. When the matte objects are set to receive GI, and shadow + affect alpha are checked, the matte surface gets DARKENED where no light hits it. This is even where there are NO shadows cast on it from other objects. If i turn rec. GI off on the matte object, the artifact goes away.
It appears that any area where the GI environment (hdri map) is blocked from hitting the matte object, it creates GI SHADOWS and darkens the matte object. This makes the background plate get darker instead of simply staying the same as it should. If there was no GI in the scene and NO lights at all, the matte object would not get darker and show shadows in the alpha...it would simply not recieve any light. This is how i need it to behave when lit by GI too.
any ideas?
thanks,
Mitch
It appears that any area where the GI environment (hdri map) is blocked from hitting the matte object, it creates GI SHADOWS and darkens the matte object. This makes the background plate get darker instead of simply staying the same as it should. If there was no GI in the scene and NO lights at all, the matte object would not get darker and show shadows in the alpha...it would simply not recieve any light. This is how i need it to behave when lit by GI too.
any ideas?
thanks,
Mitch
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