Vignette above overexposed and repositioned clip

Hey,
I am shooting a talking head video with white background. The background drop wasn't properly light the whole time, so I had to do some slight color correction within final cut that over exposes the left and right sides of the image a bit more.

What I have been trying to do now, was overlaying a vignette PNG over the whole image. It works well when I use the original frame, but there are some shots where I moved the person and whole clip to the right or left third of the frame. To cover up the empty background I just used a 100% white background image behind the clip. And in these parts it looks like the image correction is applied as well to the vignette PNG image. I get a break between where the clips end and the white background starts.

Its probabbly easier to understand with these images:

The shot I am talking about with a viginette applied


The same show without viginette (no difference between background and clip)


The mask applied to the overexposure color correction


The viginette PNG (take in mind that its background is transparent)


My timeline:


I tried to get the same effect using the build in viginette effect but encounter the exact same problem.

When you check your compo with the scopes you can see what's happening:




your vignette is applied to the added white generator, nice curve ... but your CC background behind your talent doesn't match the levels of the generator = flat/clipped white.

So, the 'sums' are different = that ugly border....

workaround: level both whites to the same level ... than apply vignette ...