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Using Mattes with Video
What is the best way to approach masking a moving subject in video? Say I want to mask the video to reveal only the person in the video, or want to remove the background sky behind mountains, there must be a more logical way than drawing a fitting matte every 1-5 frames, right?
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1 Reply
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It’s called “rotoscoping”.
First you try to key out as much of the subject as you can, then you draw a mask for the rest, and keyframe its shape parameter.
However, you shouldn’t just draw a mask every 10 frames — you should find the places where the mask shape would hit an extreme, and draw it there, letting AE interpolate from extreme to extreme. Say the person being masked stretches out his/her arm, then retracts it. You draw a mask at three points in time: arm in, arm out, and arm in. AE interpolates between the three.
Also, if parts of the person do not change shape, you draw separate masks for those parts and just keyframe their mask shape by dragging their position around, making keyframes at extreme positions.
By extremes, I don’t mean just the ends of motion, but also where motion changes direction: points of inflection.
There are other rotoscoping tips on the COW, no doubt. Search and ye shall find.
Steve
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