Background extraction info

A question about background extraction.
When invoked, does it apply your desired settings to all three channels, or just the channel you have selected on the ‘tab’?
Or another way, is it possible to test and apply BE settings to one channel, then test and apply to another channel to optimise?
I guess you can extract channels and do it that way?
I have different gradients in different channels I wish to address.

BE is computed per channels.
You don’t have to worry about .

Thank you!