Levels

Colors> Image Color Adjustments> Levels Adjustment...

The Levels adjustment can be used to alter the color range (or "exposure") of the design, including gamma adjustments, on a channel-by-channel basis. Most adjustments performed using levels consist of changing a designs input and output white point, black point, and grey point. The white point of the design is the brightest color that appears in the design, while the black point is the darkest color that will appear in the design. The grey point represents the average color of the entire design. Accordingly, you can adjust the levels of all the colors in the design by sliding the arrows of white, grey and black.