A nice feature with adjustment layers is the fact that they come with their own masks. If you are familiar with masks you know that a mask allows you to control what part of the image you want the adjustments made to.
Here is my original photo.
I like the dark background but the object needs to be lighter. Below is my resulting photo. Using an adjustment layer with levels and a layer mask.
- I created a new adjustment layer and selected levels
- I adjusted the midtones up by sliding the middle triangle to the left
- I selected the mask in this adjustment layer and filled the mask to black
- Black conceals everything
- I painted with white to reveal the levels adjustment just on the piece in the foreground
If I accidentally over painted the white and got some of the background I simply use a black paint brush to paint it away in the layer mask.
The result is the perfect image of saving the background and just making edits to the area needed.