The Adjust Color Levels filter
You can use the Adjust Color Levels filter to adjust highlights (right), shadows (left), and mid-tones (middle) in an image. The Color Levels histogram displays the tonal range of the whole image.
To adjust color levels in an image
Select an image file.
On the Window menu, click Image Editor.
Click the Adjust Color Levels filter.
In the Adjust Color Levels dialog box, the middle slider changes the intensity values of the middle range of tones without significantly changing the highlights and shadows. The outer two-level sliders set the black point and the white point of the image.