user20944: I need to fix this in post. Can I do it? 

user1950: If you shoot an evenly lit white frame you could invert it, adjust the levels so that the non-affected areas of the frame were completely black, and then add the result to the original footage. It might take some tweaking of the levels to get it right.

20944: <p>I need to fix this in post. Can I do it? <a href="https://i.stack.imgur.com/ZioUX.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ZioUX.png" alt="enter image description here"></a></p>
 1950: <p>If you shoot an evenly lit white frame you could invert it, adjust the levels so that the non-affected areas of the frame were completely black, and then add the result to the original footage. It might take some tweaking of the levels to get it right.</p>
