Replicating functionality of intersecting masks in LR/ACR into photoshop

[zuru]

The new(ish) masking options in LR/ACR are just phenomenal. There is one particular option that I would like to replicate in photoshop for a mask: "intersect". For example, I learned this trick from another photographer that when lots of trees are present in the horizon, in LR selecting "sky" and then intersecting it again with "sky" creates a much, much better selection.

Can anybody think of a way to at least emulate this "intersect" functionality in Photoshop?

[Conrad C]

A problem with Photoshop masks is that you get only one pixel mask per layer. The new masks in Lr/ACR allow mask groups, which is what allows operations such as Add/Subtract/Intersect among the mask group components. At this time in Photoshop, only a vector mask supports multiple components that can be combined with operations, as shown in the picture below.

I haven’t looked much into how you might emulate intersecting multiple pixel masks in Photoshop, but I’ll guess that one way might be to set up your two selections as different channels (in the Channels panel), then mix them into one mask using Image > Calculations. But I’m not sure what the correct settings in Calculations should be, such as the blending mode. And it still wouldn’t be as flexible as the mask groups in Lr/ACR, because it all gets baked into a single result.

[zuru]

When you do a "Select sky" operation, you see that the mask the PS creates is graded. Maybe my question should've been reframed as doing operations with these masks and not with the selection. The reason that intersecting a sky selection with itself works so well in LR is that the edges get sharper. 

Maybe I could achieve the same thing by multiplying the mask with itself, or thresholding, or something like that. But it's a lot of stuff to do vs the way LR/ACR mask intersection works so simply.