From VFXPedia

InvertedBC

This macro does inverted operations of the Brightness/Contrast tool in reversed order to restore the original color.

Used formulas:

NewColor=Color*Gain

Color=NewColor/Gain

NewColor=Color^(1/Gamma)

Color=NewColor^Gamma

NewColor=Color+(Color-0.5)*Contrast

Color=NewColor+(NewColor-0.5)/(Contrast+1)+0.5

NewColor=Color+Brightness

Color=NewColor-Brightness

NewColor=(Color-Low)/(High-Low)

Color=NewColor*(High-Low)+Low

You can make inversion of Brightness/Contrast using the Brightness/Contrast tool. In this case you need separate BC node for each parameter to apply operations in reversed order.

Use the following parameters:

InvertedHigh=High/(High-Low)

InvertedLow=-Low/(High-Low)

InvertedBrightness=-Brightness

InvertedContrast=-Contrast/(1+Contrast)

InvertedGamma=1/Gamma

InvertedGain=1/Gain