imaginary numbers for the outputs of the Gain-Offset_Gamma for gamma

Hi all,

I am using the GOG model Y=(gain*X+offset) ^gamma to fit the tone
curve of each channel of a monitor. ( X is normalized to be between 0
and 1).
My results are a negative offset and non-integer gamma. I get a
problem with the low digital values. At a low digital value, the
(gain*X+offset) is negative , and thus the (gain*X+offset) ^gamma
will be an imaginary number (gamma is around 2.3).

Can you please suggest what should I do?  Just take the real part, or
anything else?

Thanks