4.3 Lens Distortion and Overscan
A brief look at the concept of Lens Distortion and the Overscan workflow
Lens Distortion
Every camera lens creates lens distortion. The CG camera doesn’t create such artifact, the render will have straight undistorted lines. We need to apply lens distortion to the CG to make it accurately fit the footage
Original Footage
Footage has convex distortion, like a cushion
To undistort, we would need to pull the corners out
CG without Distortion
The CG has no lens distortion, all lines are straight
This can’t fit accurately on distorted original footage
CG with Lens Distortion
Applying lens distortion, now CG fits on footage
But lens distortion pushes corners inside
CG gets smaller and we’re missing image content
Overscan
The missing image content has to be rendered in a larger canvas size called Overscan
CG with Lens Distortion and Overscan
Lens distortion pushes corners in, but CG with overscan has enough image content
Overscan Workflow
Integrating overscan CG on footage would go like this
- Lens Distortion is applied to overscan CG
- Then merged with overscan footage
- Before writing out, overscan is removed
You could remove overscan from CG before merging on normal size footage, but keeping overscan thought the comp is useful, especially when operations affecting edge pixels, such as blurs, are involved