MichelB wrote: With Rusty's setup, the type of adjustment layer is indifferent. No effect. The masked (black) part of the mask and the white one are not changed.
What is very important to understand is that the upper layer is linked to the adjustment mask. The upper layer blend mode is normal, that is the pixels of the above layer will replace the values of the effect of the background copy modified by the (null) adjustment. However, the masked part will suppress the efect of the adjustment layer and its linked upper layer: the background will show through.
In this example, it is not important if the upper or lower layer is desaturated. You only have to invert the mask.
Yes, but in the interest of keeping the file size low, wouldn't the background plus a Hue/Sat adjustment layer plus masking be the optimal solution?