Lighting Effects - The Photoshop: Professional Retouching and Compositing Tips, Tricks, and Techniques - page 201

Figure 3.45
1. To first add a darkening effect, we'll add a Levels adjustment layer.
Tip
You may be tempted to use the Midtones slider to darken the image, but this also
saturates the colors, giving an unrealistic result. Instead, we'll make use of the
Output Levels setting.
2. Change the Output Levels setting of the whites to 160. You can do this by typing
in the amount or by dragging the control point toward the center of the gradient
( Figure 3.46 ) .