Adjusting Tones and Contrast with Levels
  1. Work with a Layer Adjustment. Choose Layer > New Adjustment Layer > Levels.
  2. Use the black and then the white point eyedroppers to set the darkest and lightest areas of the image. Drag the gray slider for final adjustment. If the image contains a neutral gray area, use the Gray Point eyedropper to help correct color cast.
  3. To help locate the darkest and lightest areas of an image when in the Levels adjustment dialog box try accessing the Threshold Mode in the Input Levels sliders. Hold down the Alt key on the Black and then the white slider. Drag a slider slightly while holding the Alt key down to reveal the darkest or lightest pixels in the image.
  4. Experiment with changing the Layer Blending Mode to Luminosity to help bring color back after correcting contrast with a Levels Layer Adjustment.