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Changing Camera Distortion on Tilting Camera
Hi, Everyone.
I am not an everyday user of After Effects, but am trying to pull off a temp comp for a project that is proving tricky. I’m not sure what to do and am looking for advice.
In the shot, the camera tilts down from the roof of a building to an alley below. A lot of the tiles of the roof are missing, which I painted in on one frame in Photoshop (I find Photoshop easier to paint with than AE).
Ordinarily, I would just track the phototop file to the shot, but there is massive lens distortion as the camera tilts down, which makes my single frame of the roof completely mismatch the original shot by the time the tilt is finished.
I can kind of get away with it, but it’s tehnically wrong, as when I a/b/ the VFX shot with the original plate, the painted roof is wildly off from the original.
How would one go about working on a shot like this? Would they have to undistort everything and then redistort? How would you do that? This distortion also seems to animate. Would you have to animate a distortion?
I maybe dealt with something like this in school, over a decade ago, but I’m not REALLY a VFX artist and can’t remember how to handle this. I don’t understand the physics of lens distortion. A lot of the youtube tutorials on this topic don’t really make sense to me.
Does anyone have any advice for how to handle a shot like this?
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2 Replies
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Yes Scott, you would straighten out the lens distortion, then do the tracking and patchwork, and finally re-introduce the original distortion.
If the distortion seems to be changing, then perhaps the footage was cropped or digitally stabilised ? That’s a final step that can only occur after the lens correction and tracking.
After Effects has a basic lens correction plug-in “Optics Compensation”, Red Giant has one that’s supposedly better, included in VFX plugin suite: https://www.maxon.net/en/red-giant/vfx-suite/lens-distortion-matcher
If it’s a reasonably short shot, perhaps you can even correct the lens distortion in photoshop as an image sequence.
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The Lens Distortion Matcher from Red Giant’s VFX Suite can do some magical things if you’ve got it. It’s extremely handy for working with wide-angle shots like you describe.
If you don’t have it, sometimes using Mesh Warp and manually creating the lens distortion grid can solve things, but it takes a lot of tedious work to match the distortion. Try to find a distortion grid online to help you instead of eyeballing it.
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