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Wind Gust In Grass Effect
Gave this a go in the AE forum, neglected the motion graphics note…my bad! Any ideas?
I have some head-on wide footage of a man standing in desert field full of yellow straw/grass about a foot high. I’m compositing a large object swinging down in an arc from the left to the right, and almost hitting him (he falls to the ground to avoid it)– like a wrecking ball. I want this ball to create a gust of wind through the grass as it goes by, and then once it has passed out of frame, have the grass slowly resolve back to its regular windless state.
I’ve read some threads about how to do the wind effect, basically by creating displacement maps and perhaps using the wiggler to skew out the horizontal/vertical displacement. I made a displacement map off of a radial ramp and made it track the object to follow behind it as it crosses the screen… then I masked off the area I want affected by the wind, feathered it a lot, and applied the map. This looks like it will work once it is well-tweaked. It creates the beginning of the wind effect, however, since it is just a circle the map is over too quickly and the grass returns to its normal position too quickly–it looks unnatural. Ideally I suppose the map I would want would look a “comet”, I guess… total black to almost total white at the rightmost side then slowly tapering off on the left to produce the effect of the wind slowly dying out. It seems like that would work. Any idea how I would produce this map, or even better, of any other way to make the effect look more realistic?
I also have two other questions while I’m here (I’m new to displacement maps). When the map tracks too far to the right of the screen, whatever is cut off wraps around and comes out of left frame. How do I extend it so this doesn’t occur?
This last one is really confusing me… about the time the object first comes onscreen, the grass suddenly starts to become displaced, even though the map has not reached those pixels yet– that area is still fully black on the map. They only become slightly displaced, however. When the actual map comes through they become extremely displaced as expected, but I have no idea why its displacing before the map gets there? All compositions and the ramp layer are the same dimension. Sorry for all the questions but I have much to learn. Much thanks.
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2 Replies
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You could try Distort>>Mesh Warp on the grass. Set a keyframe at the beginning right before the grass is supposed to move, and then set another at the peak of the movement. Drag around on the mesh a little to get the movement you want. Copy the first keyframe and paste it at the end where you want the movement to stop.
You may have to do this over different sections of the grass to get the intended effect at different times if you want to give the illusion of sweeping from one side of the frame to the other.
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The other possibility if you have it at your disposal is the “Puppet Tool” I don’t know much about it, but I know it can do quite a bit with moving pixels around etc.. might be what you need w/ that grass…
Im sure if you search you can find some tutorials on how to use it..
-Jeremy
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