Photoshop Elements > Levels >

Layer Masking

You can make a change in only a portion of your photograph by painting a layer mask on the photograph.

Be sure to check off as you go along.

Original

Brightened Everywhere

Original in the Background

Brighter in the Foreground

You have used a Levels adjustment layer to change a photograph overall.

Now, you want to confine the changes made to only part of the photograph. 

1) Click the Brush tool.

Because the areas to be selected were clearly demarcated, a brush with little feathering, and an opacity setting of 100%, was used.

In other situations, use brushes with feathering to blend the effect.

If you haven't already done so, go to Feathered Brush.

Make sure the Levels adjustment layer is active (highlighted).

Make sure the foreground color is black.

If you haven't already, go to Foreground & Background Colors.

2) Paint the mask on your photograph.

Where you paint with black, the foreground color, the effect of the Levels adjustment layer is concealed.

You can see the mask thumbnail in the Levels adjustment layer.

The black mask above is blocking the effect of the Levels adjustment layer in the background of the photograph.

If you haven't already done so, go to Masking.