That is going to depend on how you measure the intensity, and might depend upon the exact order of operations in the intensity measurement.
If I am someone trying to "sneak" a stego image past you, and if I know exactly how you are computing intensity, and if I can find a way to exploit round-off error in your calculation, then I would do that. It would not matter if some other way of calculating the intensity might theoretically detect the stego image: if I can find a mistake or limitation in your calculation code, I would exploit it.
