Using the Auto Levels command

The Auto Levels command moves the Levels sliders automatically to set highlights and shadows. It defines the lightest and darkest pixels in each color channel as white and black and then redistributes intermediate pixel values proportionately. Because Auto Levels adjusts each color channel individually, it may remove or introduce color casts.

By default, this feature clips the white and black pixels by 0.5%--that is, it ignores the first 0.5% of either extreme when identifying the lightest and darkest pixels in the image. This ensures that white and black values are based on representative rather than extreme pixel values.

Auto Levels gives good results when an image with an average distribution of pixel values needs a simple contrast adjustment or when an image has an overall color cast. However, adjusting the Levels or Curves (Photoshop) controls manually is more precise.

To use the Auto Levels command:

Choose Image > Adjustments > Auto Levels.

To change the amount of white and black values clipped:

Do one of the following:

• (Photoshop) Set clipping values in the Auto Correction Options dialog box. For more information, see Setting auto correction options (Photoshop).
• (ImageReady) Hold down Alt (Windows) or Option (Mac OS), and click Options in the Levels dialog box. Enter the percentage of extreme highlight and shadow pixels to ignore, and click OK. A value between 0.5% and 1% is recommended.