Here’s a tip for editing your selections in Quick Mask Mode. Near the bottom of your toolbar you’ll find two buttons that allow you to “Edit in Standard Mode” and “Edit in Quick Mask Mode”. You’ll be in standard by default. If you enter Quick Mask Mode you’ll notice everything turn red.
Everything that’s red is unselected. We’re essentially going to be painting the selection by using black and white. If you use your paintbrush and start brushing in white, the red will start erasing away and will become transparent.
If you go back into standard mode you can see your selection now.
You can either hold down SHIFT while using the Lasso Tool to draw more into your selection or go back into Quick Mask Mode to paint in more of your selection until you have the entrire subject lassoed. The beauty about Quick Mask is that you can use black to paint in a deselection, if you will.
In this instance, I had the plane selected and I Ctrl+C to copy and Ctrl+V to paste. Now the plane became separated from the background for me to manipulate separately. Just as an exercise I right clicked the background layer and chose Duplicate and proceeded to go to the top menu and choose Filter>Blur>Smart Blur with the following settings:
And this is how Quick Mask Mode can help you separate imagery elements.