<aside> 🎥 Every lens has distortion. But virtual camera used in 3D editors does not have this effect - the render always has straight lines, without distortions.
To combine CG with shooting material, it is necessary to apply lens distortion to the render. At this moment, one may encounter a problem - after applying distortion to the CG material, there might be a lack of content at the edges of the frame. This is why it is necessary to consider overscan and output the render from 3D editors with a margin, so that after applying distortion, there are no empty areas at the edge of the frame.
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This guide shows how you can apply overscan when working in different 3D packages
Script download link:
Screenshot 1 shows a grid with lens distortion. You can see how straight lines are distorted at the edges.
screenshot 1
Let's assume that the CG object is at the edge of the frame (screenshot 2)
screenshot 2
In order for a CG object to render correctly in the footage, you must apply distortion to it that corresponds to the lens. In this case, after distortion is applied, the CG part will be stretched and "tiling" will occur.
screenshot 3
In order to avoid this and CG rendering was displayed correctly for this purpose is necessary overscan. That is, at the moment of rendering additional pixels are added on the edges so that they are enough to apply distortion.
screenshot 4
To find out which overscan is needed, you can look at the bounding box settings in Nuke. The dotted box shows how much the image extends beyond the edges.