Apply the Auto Contrast adjustment

The Auto Contrast command adjusts image contrast automatically. Because Auto Contrast does not adjust channels individually, it does not introduce or remove color casts. It clips the shadow and highlight values in an image and then maps the remaining lightest and darkest pixels in the image to pure white (level 255) and pure black (level 0). This makes the highlights appear lighter and shadows appear darker.

By default, when identifying the lightest and darkest pixels in an image, Auto Contrast clips the white and black pixels by 0.5%—that is, it ignores the first 0.5% of either extreme. You can change this default using the Auto Color Correction Options found in the Levels and the Curves dialog boxes.

Auto Contrast can improve the appearance of many photographic or continuous-tone images. It does not improve flat‑color images.

Do one of the following:
• Click the Levels or Curves icon in the Adjustments panel.
• Choose Layer > New Adjustment Layer and choose either Levels or Curves. Click OK in the New Layer dialog box.
Note:
You can also choose Image > Auto Contrast to apply the adjustment directly to the image layer. Keep in mind that this method discards image information and its application is automatic. You cannot adjust any of the options in the following steps.
In the Properties panel (CC, CS6) or Adjustments panel (CS5), Alt-click (Windows) or Option-click (Mac OS) the Auto button.
Under Algorithms in the Auto Color Correction Options dialog box, select the Enhance Monochromatic Contrast option.
Specify the shadows and highlights that are clipped, and adjust the target color for the midtones.
Click OK to apply Auto Contrast.