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Use Boris Motion Key After Effects plugin in Reverse
Hi. I’d like to say in advance that I’m not an animator, I’m asking this question based on an idea an animator had about using this plugin and I’m trying to figure out if it can be done. Consequently my terminology mightn’t be correct but I’ll do my best to describe exactly what’s trying to be achieved and maybe that’ll be enough information.
The animator has a scene in which a person walks across a static shot from right to left in the foreground. In the background behind them is the wall of a building. The shot has had footage from a talking head placed onto the building and so now when the person passes the building they now pass under this layer. That is, the talking head (not 100% opacity) appears over the moving figure.
For this shot we would like to have the person walk past the wall appearing ‘above’ (or in front of) the superimposed talking head as though it were naturally a part of the scene and the person obscures it by walking past in the same way as they would obscure the wall normally. As I understand it Motion Key is for removing moving figures from static shots, could it be used to recognise a moving figure and place it in to a scene or for our purposes specifically place it over another layer? At present the shot is being painstakingly rotoscoped.
This is being done in after effects cs5 on a Mac Pro running Mac OS X 10.6.7
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4 Replies
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[James Clark] “This is being done in after effects cs5”
No, I don’t believe that Motion Key can be used in reverse but After Effects CS5 has a new Roto Brush tool which can be used to create a moving mask around the foreground subject so that you can place them on a layer above everything else. This should do exactly what you want.
~jr
http://www.johnrofrano.com
http://www.vasst.com -
John, great point about Roto Brush, I completely forgot about it. Definitely something to try in step two. You will still need a clean plate from step one (if I understand the effect correctly).
Boris Yamnitsky
BorisFX -
It sounds to that you have two separate tasks:
– create a clean plate by removing the walking person from the scene. This part can be accomplished with the BCC Motion Key filter. Make sure to roughly isolate the moving person with a rectangle or oval tool as demonstrated here:
https://www.borisfx.com/videos/BCCAVX/Motion-Key.php
the demo is done in Avid but the steps are the same or similar in AE
– Second task is to isolate a moving person and composite it on the clean plate. This is something that BCC Motion Key does not do. You may get close to this goal by using AE diff mode between clean plate and original but the edges are not going to look great. A BCC Matte Choker may be helpful here.
FWIW
Boris Yamnitsky
BorisFX -
Looks like the roto brush is what I’m after. Shame, was hoping this plugin would make the animator’s job much easier for this purpose. Thanks for the help guys
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