Projection and lens distortion ,the correct workflow ??

[coolchipper]

Hi Nukers,
Well, i am a prep artist at my vfx studio, There is one thing that i struggle a lot during my work is Lens distortion.I do lots of projection stuff everyday, and usually end up doing a grid warp over my projected patch.Well i searched a lot and got a solution that i should take out the lens distortion of a shot before projection it.I have few doubts regarding the workflow and trust me i searched the whole forum for this.thats why troubling you guys.

1.Have heard people using the overscan thing.i know its a percentage by which the footage is extended as delensing stretches the edges.But how to calculate that.ex.if i know the footage was extended 20% by the matchmove dept, then how i calculate the overscan format.?

2.What is the correct workflow. if i have a dmp of a certain frame. should i just undistort it first and then comp it over the plate or undistort the whole plate ,render ,and then comp my undistorted projection patches.?

If you can show this with a example script it will be a great help

Thanks a lot.

[Scrypnik]

Hey collchipper. I think the best is to just use the footage to CALCULATE the lens distortion. Then apply this distortion to the 3D render (output from nuke's scanline render or a render from other app like maya) and then merge this over the original DISTORTED footage. This way you never apply a transformation to the footage and mantain its quality untouch.

[hgelpke]

I've always been under the impression that it's undistort - patch - re-distort so that you are doing your cleanup on an undistorted plate.

[radders]

The lens distortion needs to be figured out during the match move process so if you are doing projection you should already know it.

Once you know the lens distortion you need to un-distort your image before you project it, then re-distort the output of your 3D projection.

As a rule, anytime you take a 2D image into the 3D environment it should be un-distorted and anything that comes out of your 3D environment should be re-distorted.

[coolchipper]

Thanks conard

The lens distortion needs to be figured out during the match move process so if you are doing projection you should already know it.

Once you know the lens distortion you need to un-distort your image before you project it, then re-distort the output of your 3D projection.

As a rule, anytime you take a 2D image into the 3D environment it should be un-distorted and anything that comes out of your 3D environment should be re-distorted.

[lamakaha]

Have a look, that is my usual workflow

[manuqc]

Hey Lamakaha,

Just downloaded your tutorial, really like it man!

Thanks for taking the time doing this, very cool!!