OK. Back at my notes. To get rid of the brightness boost inside Final Cut:
Effects, Video Filters, Levels
Input 0
Input Tolerance 98
Gamma 1.23
Output 50
Output Tolerance 100
You can't ever go back exactly because you end up splitting pixel brightness levels--you can't hit brightness value 191.5 for example.
There is a rumor that in the latest Final Cut, it's possible to turn off the boost. I don't know which FCP and whatever it is, I don't have it.
We will shortly be enjoying this very same process in HiDef. We have a Short that showed up from the client as an enormous collection of carefuly numbered stills.
Enjoy
Koz