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NOTE: Click on the thumbnails to see full size image.
After fiddling around (a lot) I've finally come up with a decent way to composite CGI onto live action using alpha channels. Read on!
Get a back plate video of your shot. Here’s mine.
Then, you need to get some 3D animation software (I’m using www.anim8or.com) and make an animated video of something. Make sure the background is black.
Also render an alpha channel of the animation, with white as 0 transparency and black as full transparency.
Now, open up your video in EffectsLab. Import your alpha channel video into the project and put it on top of your video. You should get this:
Now you need to add a grade object above the alpha video, and make a mask with it. Choose object mask, and put in these settings:
Now find your alpha video on the timeline and click the green button to disable it. Looking closely, you should notice that a band of white disappears from the edge of the CGI.
Now import your animation video, the one with the black background. Stick it on the top of your layers in the timeline:
You should find it sits quite happily on top, without any annoying colour bands round the edges.
Now for the realism. It looks all right, but to make it more convincing, you could add a shadow. Make a new grade object and place it in between your alpha file and your raw back plate.
Now make a shadow shaped mask like this one with these settings:
This should be your result:
Now for masking. When something moves in front of your animation, make a freehand mask on the alpha video. Make sure you have your mask finished to perfection before copying the mask and pasting it to everything above it. It’s important that you get your mask perfect here, otherwise you’ll be changing each one individually afterwards.
Now you may or may not want to colour correct your animation, but I thought in this case all the plane needed was a simple ambient light filter:
By the way, when you do this grading, do it to the top video – the animation with the black background.
There you go! Fairly simple and quite effective when used right! AND it means you don’t have to fork out a whole load extra for CompositeLab.
There is a final version of the video here.
It's very short, but that can be changed depending on your needs. And I know the perspective's a bit off, but oh, well...
You may have noticed that I am only using the trial version of EffectsLab. I’m trying to find new things I can do with it, and this is just one of them.