Adjustment Layers are among the most useful and powerful editing tools in Photoshop's extensive arsenal of great stuff. This technique will undoubtably improve images that you use over time. It's one I go back to again and again. Sometimes to simply fix a problem, other times to help create a look and sometimes a bit of both. 

Step 1 - Open an Image that requires some work

This image is a lovely picture, however the high exposure look has impacted on the model's face more than I want. I'd like to give the face a bit more definition by lowering the exposure. At the same time I want to bring the exposure of the model's clothes down a bit, but not as much. The background I will leave bleached as I like the effect. 

Step 2 - Apply a Levels Adjustment Layer

In the Panels Group open the tab called Adjustments.

Click on the Levels Adjustment icon (circled in red below):

Step 3 - Increase Black Levels

The Adjustments Panel will now contain the Levels Editor.

The Levels Editor is made up of 3 key items:

1. The Histogram: Shows you a graph plotting the levels of your image.
   
2. Levels Markers: These show the position on the Black (0) and White (255) pixels on the graph.
   
3. Output Levels: The output levels set the Blackness of Black and the Whiteness of White for your image, especially useful when images are over or under exposed.

Using the Levels Markers I've set the Black point up to 46 in order to increase the amount of light at the Black end of the scale, adding more contrast. 

Step 4 - Decrease White Levels

Using the Output levels I've decreased the intensity of white to 218 in order to bring more detail out in the highlights. 

The image now looks like this:

Step 5 - Setting up the Adjustment Mask 

Now open the Layers Panel: there you will see a new Adjustment Layer is sitting on top of the Background Layer. 

All the changes that have been made to the levels have been made on this Adjustment Layer rather than the original image. 

Tip: Click on the Adjustment Layers Eye icon to disable the Adjustments and see the image revert back to the original.

The object that contains all the Levels Adjustments is the Layer Mask associated with the Adjustment Layer. Select this Mask by clicking on the white thumbnail like this:

With the Mask selected we are ready to start customizing the mask in order to hide some sections of our edited image. 

Step 6 - Setting up a Brush to Edit the Mask

To start with we need to set the Foreground and Background colors to Black and White (or vice-versa) as these are the two colors needed to edit the Mask. Use the default Black and White button on the Toolbar; it's the quickest way.

Choose a Brush to paint with. The size is not important right now as I like to use the [ and ] keys to edit the brush size as I work. It's much easier to work out what size you need that way. 

I am however going to set the Brush Hardness to 60% as the feathered edge this will apply to the Mask will create a nice, hard to spot blend between the Original and the Adjusted Images.

The Opacity of the Brush also has a role to play here as a 100% opaque brush will smash holes in the Mask. I prefer a more gradual approach so I've set my Brush Opacity to 25% instead. 

Step 7 - Customising the Mask

The Mask in the Adjustment Layer is white, So I will paint onto that Mask with black in order to begin creating holes in it to reveal the unedited image on the layer below (using a white brush will do the opposite). 

Tip: if your Foreground color is set to White press X to toggle between them. 

Using the [ & ] keys I've set a brush size that will allow me to work on the Background images comfortably and I've painted black strokes over the Sky, Grass, etc. on the Mask Layer. 

Because the brushe's opacity is 25%, each pass darkens the Mask gradually, slowly revealing the original overexposed background behind the re-exposed model. This means I can stop when I think it's enough. By varying the opacity of the Mask it's easier to create a more natural-looking blend between the two layers. 

Now I'll try adding more black to the Mask around the model's Clothes, only with less intensity this time. This helps lift the clothes from the levels of the background while still giving emphasis to the face. Don't forget to change the Brush Size as you paint (using [ and ]) to get around any tricky bits.

The resulting image (left) is a nice blend between the old high exposure shot and my edited exposure shot that I am much happier with. Compare this with the original on the right:

Mastering non-destructive Adjustment Layers and the customization of their Masks is a really useful skill in Photoshop, so keep practicing!

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