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View Full Version : Measuring and correcting for lens distortion


dhenion
08-15-2006, 03:21 PM
I've been dealing with quite a few HD shoots, either on green screen or just on location, where we track the camera and composite in CG objects.

One thing I haven't been doing that I know I should to get better results is measure and correct for lens distortion. But I'm not really sure how to do this. I've been looking online for some camera grids that we can shoot on set - but once I have that - how do I take that image and correct the footage?

My guess would be to superimpose the footage of the grid with a direct image of the grid and modify/warp the footage til they match up. Is there a better way? Once I've done that should I run all my footage through that process to end up with 'corrected' raw footage that I can then use for camera tracking and compositing?

Many thanks for any help.

Pongoloid!
08-15-2006, 10:41 PM
That is a good way to do it. Or you can warp your footage with a lens correction plugin like 55mm from Digital Film Tools or PFBarrel from the Pixel Farm if you want to spend some cash.

evanfotis
08-16-2006, 07:23 AM
Does AE not have the lens correction filter of PS as optics compensation?

Pongoloid!
08-16-2006, 05:02 PM
I don't think so, but I could be wrong.

evanfotis
08-16-2006, 06:57 PM
In AE pro, go to
Effect> Distort>Optics Compensation.
from the help center: To add and match lens distortion with Optics Compensation (Pro only)
To match FOV values, layers must be the same size. However, if you select Resize, you can apply Optics Compensation again and reverse the distortion using the same value (reversed). You can then apply another effect between the two instances of Optics Compensation.
If you resize a layer using Optics Compensation and then precompose it into a larger composition, you cannot reverse the distortion using the same value until you enlarge the precomposed layer to accommodate the expanded layer.
Select the footage layer with the distortion, and choose Effect > Distort > Optics Compensation.
In the Effect Controls panel, adjust the FOV until a distorted edge or line appears straight. Note the FOV value.
Select the computer graphic layer you want to distort, and apply Optics Compensation to it using the FOV value from step 2.
Select Reverse Lens Distortion.
Remove Optics Compensation from the footage layer.

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