Photoshop Levels
Eyedroppers

Eyedropper Tool

Before

After

Figure 1.  Mouse over to see the original dark and light gray chips

The Eyedroppers are used to set the black, mid and/or white points of the tonal scale to specific areas in the image.  This, in effect, stretches the tonal range of the image to the full 0 - 255 range.

In the example in Figure 1, the black eyedropper was clicked on the dark gray chip on the left and the white eyedropper was clicked on the light gray chip on the right.  By using the black eyedropper and clicking on the dark gray, we are telling Adobe Photoshop this tone and anything darker is now black.  By using the white eyedropper and clicking on the light gray chip, we are telling Photoshop this tone and anything lighter is now white.  Mouse over the After label in Figure 1 to see the resulting image.

The eyedroppers are a good way to set black, mid and/or white points when we want to use specific areas in the image instead of the Levels histogram.  In addition, they can be used to help neutralize a color cast in an image.  Correcting color casts using Levels is discussed on the Levels Color Correction page.