Friends who work in the VFX compositing departments always talk about how they integrate the cg elements into the video by doing something called "lifting the blacks". They can say it better, but this is what I understood the process as.
When you render out your 3D elements you can get a realistic output but it won't match to the real environment they should be part of. So with a bit of tooling and artistic eyeballing they match the darkest point of the real video to the darkest part of the cg render resulting in the feeling of the 3D element integrated in the real environment. They call it "lifting the blacks" because usually the 3D elements which are rendered are pretty dark, as in the shadows and stuff being black and they need to saturate them and add more light to be able to fit into the real environment, which is mostly done in a compositing software like Nuke.
When you render out your 3D elements you can get a realistic output but it won't match to the real environment they should be part of. So with a bit of tooling and artistic eyeballing they match the darkest point of the real video to the darkest part of the cg render resulting in the feeling of the 3D element integrated in the real environment. They call it "lifting the blacks" because usually the 3D elements which are rendered are pretty dark, as in the shadows and stuff being black and they need to saturate them and add more light to be able to fit into the real environment, which is mostly done in a compositing software like Nuke.