Page 213 - Photoshop for Lightroom Users – Scott Kelby 2nd Edition

lock in your transformation.

Step Six:
Of course, you can see a hard edge on our flipped wall layer, so we’re going to softly paint that edge away so you don’t see where the new wall starts and
the old one begins—we’ll create a smooth transition between the two. For erasing edges like this, we don’t get the Eraser tool (it’s too unforgiving and uses
a hard-edged brush by default). For stuff like this (hiding edges), we go to the bottom of the Layers panel and click the Add Layer Mask icon (the third icon
from the left) to add a layer mask. That way, if we make a mistake while we’re painting away that edge, we can just switch our Foreground color to white
and paint over our mistake. Press D, then X to make sure your Foreground color is set to black, get the Brush tool (B) from the Toolbar, choose a large,
soft-edged brush from the Brush Picker up in the Options Bar, and then paint right over that hard edge to mask it away (as seen here).