Today’s Question: When creating targeted adjustments in Photoshop, is there a way to duplicate a layer mask (for the sky, for example) but for the opposite area (the foreground, for example)? Sometimes I want to apply some adjustments to the sky, and then apply different adjustments to the foreground, and I’m looking for a shortcut.
Tim’s Quick Answer: You can indeed create a layer mask in Photoshop that is the opposite of an existing layer mask. There are various approaches you could take, but I generally use a selection for this purpose. Start by holding the Ctrl key on Windows or the Command key on Macintosh and clicking on the thumbnail for the existing layer mask on the Layers panel. This will create a selection based on that mask. Then choose Select > Inverse from the menu to create the opposite selection. Finally, add a new adjustment layer, which will now have a layer mask that is the opposite of the existing layer mask.
More Detail: It is important to keep in mind that in many cases you will need to perform some fine-tuning for the inverted duplicate layer mask you created. Chances are, for example, you have applied some feathering to the original layer mask. That feathering will be reversed for the duplicate layer mask.
Because of that feathering, there will be an area along the transition edges of the two layer masks where very little adjustment is applied. The adjustment for the sky, for example, will taper off before reaching the foreground, and the adjustment for the foreground will taper off before reaching the sky.
The result can be an obvious area where the adjustments don’t blend together very well. You can use the Refine Mask controls (by clicking the Mask Edge button on the Masks tab of the Properties panel) to improve the blending. The “Shift Edge” control in particular can be especially helpful for this purpose.
So, while some refinement to the individual masks may be necessary (depending on the nature of the mask and the strength of the adjustments applied), it is quite easy to create a copy of an existing layer mask with the opposite shape.