The Output Levels sliders let you set the shadow and highlight levels to compress the image into a range less than 0 to 255. Use this adjustment to preserve the shadow and highlight details when an image is being printed on a press whose characteristics you know. For example, suppose there are important image details in the highlights with a value of 245, and the printing press that you’re using won’t hold a dot smaller than 5%. You can pull the highlight slider to level 242 (which is a 5% dot on the press) to shift the highlight detail from 245 to 242. Now, the highlight detail will safely print on that press.

Generally, it is not a good idea to use the Output Levels sliders to target images with specular highlights. Your specular highlight will look gray rather than blow out to pure white. Use the highlight eyedropper for images with specular highlights.

Targeting shadows and highlights with Output Levels sliders