Using the Auto Contrast command

The Auto Contrast command adjusts the overall contrast and mixture of colors in an RGB image automatically. Because it does not adjust channels individually, Auto Contrast does not introduce or remove color casts. It maps the lightest and darkest pixels in the image to white and black, which makes highlights appear lighter and shadows appear darker.

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. This ensures that white and black values are based on representative rather than extreme pixel values.

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

To use the Auto Contrast command:

Choose Image > Adjustments > Auto Contrast.

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.