have you tried to extract the vignetting pattern form the captures and using it to normalize them? My first try would be to calculate the median grayscale image of all 9000 captures and then using this to normalize the intensity.
Thanks for sharing constexpr-everything, i was looking for a tool like that. Did you consider to implement it as an (implicit) optimization step for clang? Also, i like how short the source is, i think it will help me getting started with libtooling.